| Message ID | 20230830231758.2561402-3-sjg@chromium.org |
|---|---|
| State | New |
| Headers | show |
| Series | [v5,1/4] Add reserved-memory | expand |
On Thu, 31 Aug 2023 at 01:18, Simon Glass <sjg@chromium.org> wrote: > > The Devicetree specification skips over handling of a logical view of > the memory map, pointing users to the UEFI specification. > > It is common to split firmware into 'Platform Init', which does the > initial hardware setup and a "Payload" which selects the OS to be booted. > Thus an handover interface is required between these two pieces. > > Where UEFI boot-time services are not available, but UEFI firmware is > present on either side of this interface, information about memory usage > and attributes must be presented to the "Payload" in some form. > I don't think the UEFI references are needed or helpful here. > This aims to provide an small schema addition for this mapping. > > For now, no attempt is made to create an exhaustive binding, so there are > some example types listed. More can be added later. > > The compatible string is not included, since the node name is enough to > indicate the purpose of a node, as per the existing reserved-memory > schema. > > This binding does not include a binding for the memory 'attribute' > property, defined by EFI_BOOT_SERVICES.GetMemoryMap(). It may be useful > to have that as well, but perhaps not as a bit mask. > > Signed-off-by: Simon Glass <sjg@chromium.org> > --- > > Changes in v5: > - Drop the memory-map node (should have done that in v4) > - Tidy up schema a bit > > Changes in v4: > - Make use of the reserved-memory node instead of creating a new one > > Changes in v3: > - Reword commit message again > - cc a lot more people, from the FFI patch > - Split out the attributes into the /memory nodes > > Changes in v2: > - Reword commit message > > .../reserved-memory/common-reserved.yaml | 53 +++++++++++++++++++ > 1 file changed, 53 insertions(+) > create mode 100644 dtschema/schemas/reserved-memory/common-reserved.yaml > > diff --git a/dtschema/schemas/reserved-memory/common-reserved.yaml b/dtschema/schemas/reserved-memory/common-reserved.yaml > new file mode 100644 > index 0000000..d1b466b > --- /dev/null > +++ b/dtschema/schemas/reserved-memory/common-reserved.yaml > @@ -0,0 +1,53 @@ > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/reserved-memory/common-reserved.yaml# > +$schema: http://devicetree.org/meta-schemas/core.yaml# > + > +title: Common memory reservations > + > +description: | > + Specifies that the reserved memory region can be used for the purpose > + indicated by its node name. > + > + Clients may reuse this reserved memory if they understand what it is for. > + > +maintainers: > + - Simon Glass <sjg@chromium.org> > + > +allOf: > + - $ref: reserved-memory.yaml > + > +properties: > + $nodename: > + enum: > + - acpi-reclaim > + - acpi-nvs > + - boot-code > + - boot-data > + - runtime-code > + - runtime-data > + These types are used by firmware to describe the nature of certain memory regions to the OS. Boot code and data can be discarded, as well as ACPI reclaim after its contents have been consumed. Runtime code and data need to be mapped for runtime features to work. When one firmware phase communicates the purpose of a certain memory reservation to another, it is typically not limited to whether its needs to be preserved and when it needs to be mapped (and with which attributes). I'd expect a memory reservation appearing under this node to have a clearly defined purpose, and the subsequent phases need to be able to discover this information. For example, a communication buffer for secure<->non-secure communication or a page with spin tables used by PSCI. None of the proposed labels are appropriate for this, and I'd much rather have a compatible string or some other property that clarifies the nature in a more suitable way. Note that 'no-map' already exists to indicate that the CPU should not map this memory unless it does so for the specific purpose that the reservation was made for. > + reg: > + description: region of memory that is reserved for the purpose indicated > + by the node name. > + > +required: > + - reg > + > +unevaluatedProperties: false > + > +examples: > + - | > + reserved-memory { > + #address-cells = <1>; > + #size-cells = <1>; > + > + boot-code@12340000 { > + reg = <0x12340000 0x00800000>; > + }; > + > + boot-data@43210000 { > + reg = <0x43210000 0x00800000>; > + }; > + }; > -- > 2.42.0.rc2.253.gd59a3bf2b4-goog >
On Wed, 6 Sept 2023 at 18:50, Simon Glass <sjg@chromium.org> wrote: > > Hi Ard, > > On Wed, Sep 6, 2023, 10:09 Ard Biesheuvel <ardb@kernel.org> wrote: >> >> On Wed, 6 Sept 2023 at 16:54, Simon Glass <sjg@chromium.org> wrote: >> > >> > Hi Rob, Ard, >> > >> > On Wed, 6 Sept 2023 at 08:34, Rob Herring <robh@kernel.org> wrote: >> > > >> > > On Tue, Sep 5, 2023 at 4:44 PM Ard Biesheuvel <ardb@kernel.org> wrote: >> > > > >> > > > On Thu, 31 Aug 2023 at 01:18, Simon Glass <sjg@chromium.org> wrote: >> > > > > >> > > > > The Devicetree specification skips over handling of a logical view of >> > > > > the memory map, pointing users to the UEFI specification. >> > > > > >> > > > > It is common to split firmware into 'Platform Init', which does the >> > > > > initial hardware setup and a "Payload" which selects the OS to be booted. >> > > > > Thus an handover interface is required between these two pieces. >> > > > > >> > > > > Where UEFI boot-time services are not available, but UEFI firmware is >> > > > > present on either side of this interface, information about memory usage >> > > > > and attributes must be presented to the "Payload" in some form. >> > > > > >> > > > >> > > > I don't think the UEFI references are needed or helpful here. >> > > > >> > > > > This aims to provide an small schema addition for this mapping. >> > > > > >> > > > > For now, no attempt is made to create an exhaustive binding, so there are >> > > > > some example types listed. More can be added later. >> > > > > >> > > > > The compatible string is not included, since the node name is enough to >> > > > > indicate the purpose of a node, as per the existing reserved-memory >> > > > > schema. >> > > >> > > Node names reflect the 'class', but not what's specifically in the >> > > node. So really, all reserved-memory nodes should have the same name, >> > > but that ship already sailed for existing users. 'compatible' is the >> > > right thing here. As to what the node name should be, well, we haven't >> > > defined that. I think we just used 'memory' on some platforms. >> > >> > OK >> > >> > > >> > > > > This binding does not include a binding for the memory 'attribute' >> > > > > property, defined by EFI_BOOT_SERVICES.GetMemoryMap(). It may be useful >> > > > > to have that as well, but perhaps not as a bit mask. >> > > > > >> > > > > Signed-off-by: Simon Glass <sjg@chromium.org> >> > > > > --- >> > > > > >> > > > > Changes in v5: >> > > > > - Drop the memory-map node (should have done that in v4) >> > > > > - Tidy up schema a bit >> > > > > >> > > > > Changes in v4: >> > > > > - Make use of the reserved-memory node instead of creating a new one >> > > > > >> > > > > Changes in v3: >> > > > > - Reword commit message again >> > > > > - cc a lot more people, from the FFI patch >> > > > > - Split out the attributes into the /memory nodes >> > > > > >> > > > > Changes in v2: >> > > > > - Reword commit message >> > > > > >> > > > > .../reserved-memory/common-reserved.yaml | 53 +++++++++++++++++++ >> > > > > 1 file changed, 53 insertions(+) >> > > > > create mode 100644 dtschema/schemas/reserved-memory/common-reserved.yaml >> > > > > >> > > > > diff --git a/dtschema/schemas/reserved-memory/common-reserved.yaml b/dtschema/schemas/reserved-memory/common-reserved.yaml >> > > > > new file mode 100644 >> > > > > index 0000000..d1b466b >> > > > > --- /dev/null >> > > > > +++ b/dtschema/schemas/reserved-memory/common-reserved.yaml >> > > > > @@ -0,0 +1,53 @@ >> > > > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause >> > > > > +%YAML 1.2 >> > > > > +--- >> > > > > +$id: http://devicetree.org/schemas/reserved-memory/common-reserved.yaml# >> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml# >> > > > > + >> > > > > +title: Common memory reservations >> > > > > + >> > > > > +description: | >> > > > > + Specifies that the reserved memory region can be used for the purpose >> > > > > + indicated by its node name. >> > > > > + >> > > > > + Clients may reuse this reserved memory if they understand what it is for. >> > > > > + >> > > > > +maintainers: >> > > > > + - Simon Glass <sjg@chromium.org> >> > > > > + >> > > > > +allOf: >> > > > > + - $ref: reserved-memory.yaml >> > > > > + >> > > > > +properties: >> > > > > + $nodename: >> > > > > + enum: >> > > > > + - acpi-reclaim >> > > > > + - acpi-nvs >> > > > > + - boot-code >> > > > > + - boot-data >> > > > > + - runtime-code >> > > > > + - runtime-data >> > > > > + >> > > > >> > > > These types are used by firmware to describe the nature of certain >> > > > memory regions to the OS. Boot code and data can be discarded, as well >> > > > as ACPI reclaim after its contents have been consumed. Runtime code >> > > > and data need to be mapped for runtime features to work. >> > > > >> > > > When one firmware phase communicates the purpose of a certain memory >> > > > reservation to another, it is typically not limited to whether its >> > > > needs to be preserved and when it needs to be mapped (and with which >> > > > attributes). I'd expect a memory reservation appearing under this node >> > > > to have a clearly defined purpose, and the subsequent phases need to >> > > > be able to discover this information. >> > > > >> > > > For example, a communication buffer for secure<->non-secure >> > > > communication or a page with spin tables used by PSCI. None of the >> > > > proposed labels are appropriate for this, and I'd much rather have a >> > > > compatible string or some other property that clarifies the nature in >> > > > a more suitable way. Note that 'no-map' already exists to indicate >> > > > that the CPU should not map this memory unless it does so for the >> > > > specific purpose that the reservation was made for. >> > > >> > > I agree. I think compatible is the better approach. Some property like >> > > 'discard' may not be sufficient information if the OS needs to consume >> > > the region first and then discard it. Better to state exactly what's >> > > there and then the OS can imply the rest. >> > >> > OK, so what sort of compatible strings? >> > >> > How about: >> > "acpi-reclaim" - holds ACPI tables; memory can be reclaimed once the >> > tables are read and no-longer needed >> >> ACPI reclaim is a policy, not a purpose. This memory could contain >> many different things. >> >> > "boot-code" - holds boot code; memory can be reclaimed once the boot >> > phase is complete >> > "runtime-code" - holds runtime code; memory can be reclaimed only if >> > this code will not be used from that point >> > >> >> These are also policies. They can be inferred from the purpose. >> >> > etc. We can then have more specific compatibles, like: >> > >> > "psci-spin-table" - holds PSCI spin tables >> > >> > so you could do: >> > >> > compatible = "runtime-code", "psci-spin-table"; >> > >> >> I understand that this binding targets firmware<->firmware rather than >> firmware<->OS, which makes it much more difficult to keep it both >> generic and sufficiently descriptive. >> >> However, I still feel that all the overlap with UEFI memory types is >> not what we want here. UEFI knows how to manage its own memory map, >> what it needs to know is what memory is already in use and for which >> exact purpose. Whether or not that implies that the memory can be >> freed at some point or can be mapped or not should follow from that. > > > Can you please make a suggestion? I am unsure what you are looking for. > I'm happy to help flesh this out, but you still have not provided us with an actual use case, so I can only draw from my own experience putting together firmware for virtual and physical ARM machines. All the ACPI and UEFI lingo needs to be dropped. This is relevant only to the OS, and only if the prior stage exposes UEFI interfaces, in which case it does not need this binding. So on one side, there is the requirement for each memory reservation to be described with sufficient detail so that a subsequent boot stage (firmware or OS) can use it for its intended purpose, provided that this boot stage is aware of its purpose (i.e., it has a driver that matches on the compatible string in question, and actually maps/uses the memory) On the other side, we need to describe how a memory reservation should be treated if the boot stage doesn't know its purpose, has no interest in using it or has consumed the contents and has no longer a need for the region. We already have no-map to describe that the memory should never be mapped (and this may be disregarded by an actual driver for the region). I imagine we might add 'discardable' as a boolean DT property, meaning that stage N may use the memory whichever way it wants if it is not going to use it for its intended purpose, provided that it deletes the node from the DT before passing it on to stage N+1. One thing that needs to be clarified is how this binding interacts with /memory nodes. I assume that currently, /reserved-memory is independent, i.e., it could describe mappable memory that is not covered by /memory at all. If this is the case, we have to decide whether or not discardable regions can be treated in the same way, or whether we should require that discardable regions are covered by /memory.
Hi Ard, On Thu, 7 Sept 2023 at 07:31, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Wed, 6 Sept 2023 at 18:50, Simon Glass <sjg@chromium.org> wrote: > > > > Hi Ard, > > > > On Wed, Sep 6, 2023, 10:09 Ard Biesheuvel <ardb@kernel.org> wrote: > >> > >> On Wed, 6 Sept 2023 at 16:54, Simon Glass <sjg@chromium.org> wrote: > >> > > >> > Hi Rob, Ard, > >> > > >> > On Wed, 6 Sept 2023 at 08:34, Rob Herring <robh@kernel.org> wrote: > >> > > > >> > > On Tue, Sep 5, 2023 at 4:44 PM Ard Biesheuvel <ardb@kernel.org> wrote: > >> > > > > >> > > > On Thu, 31 Aug 2023 at 01:18, Simon Glass <sjg@chromium.org> wrote: > >> > > > > > >> > > > > The Devicetree specification skips over handling of a logical view of > >> > > > > the memory map, pointing users to the UEFI specification. > >> > > > > > >> > > > > It is common to split firmware into 'Platform Init', which does the > >> > > > > initial hardware setup and a "Payload" which selects the OS to be booted. > >> > > > > Thus an handover interface is required between these two pieces. > >> > > > > > >> > > > > Where UEFI boot-time services are not available, but UEFI firmware is > >> > > > > present on either side of this interface, information about memory usage > >> > > > > and attributes must be presented to the "Payload" in some form. > >> > > > > > >> > > > > >> > > > I don't think the UEFI references are needed or helpful here. > >> > > > > >> > > > > This aims to provide an small schema addition for this mapping. > >> > > > > > >> > > > > For now, no attempt is made to create an exhaustive binding, so there are > >> > > > > some example types listed. More can be added later. > >> > > > > > >> > > > > The compatible string is not included, since the node name is enough to > >> > > > > indicate the purpose of a node, as per the existing reserved-memory > >> > > > > schema. > >> > > > >> > > Node names reflect the 'class', but not what's specifically in the > >> > > node. So really, all reserved-memory nodes should have the same name, > >> > > but that ship already sailed for existing users. 'compatible' is the > >> > > right thing here. As to what the node name should be, well, we haven't > >> > > defined that. I think we just used 'memory' on some platforms. > >> > > >> > OK > >> > > >> > > > >> > > > > This binding does not include a binding for the memory 'attribute' > >> > > > > property, defined by EFI_BOOT_SERVICES.GetMemoryMap(). It may be useful > >> > > > > to have that as well, but perhaps not as a bit mask. > >> > > > > > >> > > > > Signed-off-by: Simon Glass <sjg@chromium.org> > >> > > > > --- > >> > > > > > >> > > > > Changes in v5: > >> > > > > - Drop the memory-map node (should have done that in v4) > >> > > > > - Tidy up schema a bit > >> > > > > > >> > > > > Changes in v4: > >> > > > > - Make use of the reserved-memory node instead of creating a new one > >> > > > > > >> > > > > Changes in v3: > >> > > > > - Reword commit message again > >> > > > > - cc a lot more people, from the FFI patch > >> > > > > - Split out the attributes into the /memory nodes > >> > > > > > >> > > > > Changes in v2: > >> > > > > - Reword commit message > >> > > > > > >> > > > > .../reserved-memory/common-reserved.yaml | 53 +++++++++++++++++++ > >> > > > > 1 file changed, 53 insertions(+) > >> > > > > create mode 100644 dtschema/schemas/reserved-memory/common-reserved.yaml > >> > > > > > >> > > > > diff --git a/dtschema/schemas/reserved-memory/common-reserved.yaml b/dtschema/schemas/reserved-memory/common-reserved.yaml > >> > > > > new file mode 100644 > >> > > > > index 0000000..d1b466b > >> > > > > --- /dev/null > >> > > > > +++ b/dtschema/schemas/reserved-memory/common-reserved.yaml > >> > > > > @@ -0,0 +1,53 @@ > >> > > > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause > >> > > > > +%YAML 1.2 > >> > > > > +--- > >> > > > > +$id: http://devicetree.org/schemas/reserved-memory/common-reserved.yaml# > >> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml# > >> > > > > + > >> > > > > +title: Common memory reservations > >> > > > > + > >> > > > > +description: | > >> > > > > + Specifies that the reserved memory region can be used for the purpose > >> > > > > + indicated by its node name. > >> > > > > + > >> > > > > + Clients may reuse this reserved memory if they understand what it is for. > >> > > > > + > >> > > > > +maintainers: > >> > > > > + - Simon Glass <sjg@chromium.org> > >> > > > > + > >> > > > > +allOf: > >> > > > > + - $ref: reserved-memory.yaml > >> > > > > + > >> > > > > +properties: > >> > > > > + $nodename: > >> > > > > + enum: > >> > > > > + - acpi-reclaim > >> > > > > + - acpi-nvs > >> > > > > + - boot-code > >> > > > > + - boot-data > >> > > > > + - runtime-code > >> > > > > + - runtime-data > >> > > > > + > >> > > > > >> > > > These types are used by firmware to describe the nature of certain > >> > > > memory regions to the OS. Boot code and data can be discarded, as well > >> > > > as ACPI reclaim after its contents have been consumed. Runtime code > >> > > > and data need to be mapped for runtime features to work. > >> > > > > >> > > > When one firmware phase communicates the purpose of a certain memory > >> > > > reservation to another, it is typically not limited to whether its > >> > > > needs to be preserved and when it needs to be mapped (and with which > >> > > > attributes). I'd expect a memory reservation appearing under this node > >> > > > to have a clearly defined purpose, and the subsequent phases need to > >> > > > be able to discover this information. > >> > > > > >> > > > For example, a communication buffer for secure<->non-secure > >> > > > communication or a page with spin tables used by PSCI. None of the > >> > > > proposed labels are appropriate for this, and I'd much rather have a > >> > > > compatible string or some other property that clarifies the nature in > >> > > > a more suitable way. Note that 'no-map' already exists to indicate > >> > > > that the CPU should not map this memory unless it does so for the > >> > > > specific purpose that the reservation was made for. > >> > > > >> > > I agree. I think compatible is the better approach. Some property like > >> > > 'discard' may not be sufficient information if the OS needs to consume > >> > > the region first and then discard it. Better to state exactly what's > >> > > there and then the OS can imply the rest. > >> > > >> > OK, so what sort of compatible strings? > >> > > >> > How about: > >> > "acpi-reclaim" - holds ACPI tables; memory can be reclaimed once the > >> > tables are read and no-longer needed > >> > >> ACPI reclaim is a policy, not a purpose. This memory could contain > >> many different things. > >> > >> > "boot-code" - holds boot code; memory can be reclaimed once the boot > >> > phase is complete > >> > "runtime-code" - holds runtime code; memory can be reclaimed only if > >> > this code will not be used from that point > >> > > >> > >> These are also policies. They can be inferred from the purpose. > >> > >> > etc. We can then have more specific compatibles, like: > >> > > >> > "psci-spin-table" - holds PSCI spin tables > >> > > >> > so you could do: > >> > > >> > compatible = "runtime-code", "psci-spin-table"; > >> > > >> > >> I understand that this binding targets firmware<->firmware rather than > >> firmware<->OS, which makes it much more difficult to keep it both > >> generic and sufficiently descriptive. > >> > >> However, I still feel that all the overlap with UEFI memory types is > >> not what we want here. UEFI knows how to manage its own memory map, > >> what it needs to know is what memory is already in use and for which > >> exact purpose. Whether or not that implies that the memory can be > >> freed at some point or can be mapped or not should follow from that. > > > > > > Can you please make a suggestion? I am unsure what you are looking for. > > > > I'm happy to help flesh this out, but you still have not provided us > with an actual use case, so I can only draw from my own experience > putting together firmware for virtual and physical ARM machines. I did explain that this is needed when Tianocore is on both sides of the interface, since Platform Init places some things in memory and the Payload needs to preserve them there, and/or know where they are. I think the problem might be that you don't agree with that, but it seems to be a fact, so I am not sure how I can alter it. Please can you clearly explain which part of the use case you are missing. > > All the ACPI and UEFI lingo needs to be dropped. This is relevant only > to the OS, and only if the prior stage exposes UEFI interfaces, in > which case it does not need this binding. OK I can drop those from the commit message. > > So on one side, there is the requirement for each memory reservation > to be described with sufficient detail so that a subsequent boot stage > (firmware or OS) can use it for its intended purpose, provided that > this boot stage is aware of its purpose (i.e., it has a driver that > matches on the compatible string in question, and actually maps/uses > the memory) > > On the other side, we need to describe how a memory reservation should > be treated if the boot stage doesn't know its purpose, has no interest > in using it or has consumed the contents and has no longer a need for > the region. We already have no-map to describe that the memory should > never be mapped (and this may be disregarded by an actual driver for > the region). I imagine we might add 'discardable' as a boolean DT > property, meaning that stage N may use the memory whichever way it > wants if it is not going to use it for its intended purpose, provided > that it deletes the node from the DT before passing it on to stage > N+1. OK. For now I think that everything is discardable, so long as the Payload knows the purpose and that it not needed. That is what Rob seemed to be saying. If we add 'discardable', does that mean that things default to non-discardable? Would that not be a change of behaviour for existing users? > > One thing that needs to be clarified is how this binding interacts > with /memory nodes. I assume that currently, /reserved-memory is > independent, i.e., it could describe mappable memory that is not > covered by /memory at all. If this is the case, we have to decide > whether or not discardable regions can be treated in the same way, or > whether we should require that discardable regions are covered by > /memory. I would expect all memory to be described in /memory nodes. What is the use case for omitting it? Are you thinking of SRAM, etc? Regards, Simon
On Thu, 7 Sept 2023 at 16:50, Simon Glass <sjg@chromium.org> wrote: > > Hi Ard, > > On Thu, 7 Sept 2023 at 08:12, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Thu, 7 Sept 2023 at 15:56, Simon Glass <sjg@chromium.org> wrote: > > > > > > Hi Ard, > > > > > > On Thu, 7 Sept 2023 at 07:31, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > > > On Wed, 6 Sept 2023 at 18:50, Simon Glass <sjg@chromium.org> wrote: > > > > > > > > > > Hi Ard, > > > > > > > > > > On Wed, Sep 6, 2023, 10:09 Ard Biesheuvel <ardb@kernel.org> wrote: > > > > >> > > > > >> On Wed, 6 Sept 2023 at 16:54, Simon Glass <sjg@chromium.org> wrote: > > > > >> > > > > > >> > Hi Rob, Ard, > > > > >> > > > > > >> > On Wed, 6 Sept 2023 at 08:34, Rob Herring <robh@kernel.org> wrote: > > > > >> > > > > > > >> > > On Tue, Sep 5, 2023 at 4:44 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > >> > > > > > > > >> > > > On Thu, 31 Aug 2023 at 01:18, Simon Glass <sjg@chromium.org> wrote: > > > > >> > > > > > > > > >> > > > > The Devicetree specification skips over handling of a logical view of > > > > >> > > > > the memory map, pointing users to the UEFI specification. > > > > >> > > > > > > > > >> > > > > It is common to split firmware into 'Platform Init', which does the > > > > >> > > > > initial hardware setup and a "Payload" which selects the OS to be booted. > > > > >> > > > > Thus an handover interface is required between these two pieces. > > > > >> > > > > > > > > >> > > > > Where UEFI boot-time services are not available, but UEFI firmware is > > > > >> > > > > present on either side of this interface, information about memory usage > > > > >> > > > > and attributes must be presented to the "Payload" in some form. > > > > >> > > > > > > > > >> > > > > > > > >> > > > I don't think the UEFI references are needed or helpful here. > > > > >> > > > > > > > >> > > > > This aims to provide an small schema addition for this mapping. > > > > >> > > > > > > > > >> > > > > For now, no attempt is made to create an exhaustive binding, so there are > > > > >> > > > > some example types listed. More can be added later. > > > > >> > > > > > > > > >> > > > > The compatible string is not included, since the node name is enough to > > > > >> > > > > indicate the purpose of a node, as per the existing reserved-memory > > > > >> > > > > schema. > > > > >> > > > > > > >> > > Node names reflect the 'class', but not what's specifically in the > > > > >> > > node. So really, all reserved-memory nodes should have the same name, > > > > >> > > but that ship already sailed for existing users. 'compatible' is the > > > > >> > > right thing here. As to what the node name should be, well, we haven't > > > > >> > > defined that. I think we just used 'memory' on some platforms. > > > > >> > > > > > >> > OK > > > > >> > > > > > >> > > > > > > >> > > > > This binding does not include a binding for the memory 'attribute' > > > > >> > > > > property, defined by EFI_BOOT_SERVICES.GetMemoryMap(). It may be useful > > > > >> > > > > to have that as well, but perhaps not as a bit mask. > > > > >> > > > > > > > > >> > > > > Signed-off-by: Simon Glass <sjg@chromium.org> > > > > >> > > > > --- > > > > >> > > > > > > > > >> > > > > Changes in v5: > > > > >> > > > > - Drop the memory-map node (should have done that in v4) > > > > >> > > > > - Tidy up schema a bit > > > > >> > > > > > > > > >> > > > > Changes in v4: > > > > >> > > > > - Make use of the reserved-memory node instead of creating a new one > > > > >> > > > > > > > > >> > > > > Changes in v3: > > > > >> > > > > - Reword commit message again > > > > >> > > > > - cc a lot more people, from the FFI patch > > > > >> > > > > - Split out the attributes into the /memory nodes > > > > >> > > > > > > > > >> > > > > Changes in v2: > > > > >> > > > > - Reword commit message > > > > >> > > > > > > > > >> > > > > .../reserved-memory/common-reserved.yaml | 53 +++++++++++++++++++ > > > > >> > > > > 1 file changed, 53 insertions(+) > > > > >> > > > > create mode 100644 dtschema/schemas/reserved-memory/common-reserved.yaml > > > > >> > > > > > > > > >> > > > > diff --git a/dtschema/schemas/reserved-memory/common-reserved.yaml b/dtschema/schemas/reserved-memory/common-reserved.yaml > > > > >> > > > > new file mode 100644 > > > > >> > > > > index 0000000..d1b466b > > > > >> > > > > --- /dev/null > > > > >> > > > > +++ b/dtschema/schemas/reserved-memory/common-reserved.yaml > > > > >> > > > > @@ -0,0 +1,53 @@ > > > > >> > > > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause > > > > >> > > > > +%YAML 1.2 > > > > >> > > > > +--- > > > > >> > > > > +$id: http://devicetree.org/schemas/reserved-memory/common-reserved.yaml# > > > > >> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml# > > > > >> > > > > + > > > > >> > > > > +title: Common memory reservations > > > > >> > > > > + > > > > >> > > > > +description: | > > > > >> > > > > + Specifies that the reserved memory region can be used for the purpose > > > > >> > > > > + indicated by its node name. > > > > >> > > > > + > > > > >> > > > > + Clients may reuse this reserved memory if they understand what it is for. > > > > >> > > > > + > > > > >> > > > > +maintainers: > > > > >> > > > > + - Simon Glass <sjg@chromium.org> > > > > >> > > > > + > > > > >> > > > > +allOf: > > > > >> > > > > + - $ref: reserved-memory.yaml > > > > >> > > > > + > > > > >> > > > > +properties: > > > > >> > > > > + $nodename: > > > > >> > > > > + enum: > > > > >> > > > > + - acpi-reclaim > > > > >> > > > > + - acpi-nvs > > > > >> > > > > + - boot-code > > > > >> > > > > + - boot-data > > > > >> > > > > + - runtime-code > > > > >> > > > > + - runtime-data > > > > >> > > > > + > > > > >> > > > > > > > >> > > > These types are used by firmware to describe the nature of certain > > > > >> > > > memory regions to the OS. Boot code and data can be discarded, as well > > > > >> > > > as ACPI reclaim after its contents have been consumed. Runtime code > > > > >> > > > and data need to be mapped for runtime features to work. > > > > >> > > > > > > > >> > > > When one firmware phase communicates the purpose of a certain memory > > > > >> > > > reservation to another, it is typically not limited to whether its > > > > >> > > > needs to be preserved and when it needs to be mapped (and with which > > > > >> > > > attributes). I'd expect a memory reservation appearing under this node > > > > >> > > > to have a clearly defined purpose, and the subsequent phases need to > > > > >> > > > be able to discover this information. > > > > >> > > > > > > > >> > > > For example, a communication buffer for secure<->non-secure > > > > >> > > > communication or a page with spin tables used by PSCI. None of the > > > > >> > > > proposed labels are appropriate for this, and I'd much rather have a > > > > >> > > > compatible string or some other property that clarifies the nature in > > > > >> > > > a more suitable way. Note that 'no-map' already exists to indicate > > > > >> > > > that the CPU should not map this memory unless it does so for the > > > > >> > > > specific purpose that the reservation was made for. > > > > >> > > > > > > >> > > I agree. I think compatible is the better approach. Some property like > > > > >> > > 'discard' may not be sufficient information if the OS needs to consume > > > > >> > > the region first and then discard it. Better to state exactly what's > > > > >> > > there and then the OS can imply the rest. > > > > >> > > > > > >> > OK, so what sort of compatible strings? > > > > >> > > > > > >> > How about: > > > > >> > "acpi-reclaim" - holds ACPI tables; memory can be reclaimed once the > > > > >> > tables are read and no-longer needed > > > > >> > > > > >> ACPI reclaim is a policy, not a purpose. This memory could contain > > > > >> many different things. > > > > >> > > > > >> > "boot-code" - holds boot code; memory can be reclaimed once the boot > > > > >> > phase is complete > > > > >> > "runtime-code" - holds runtime code; memory can be reclaimed only if > > > > >> > this code will not be used from that point > > > > >> > > > > > >> > > > > >> These are also policies. They can be inferred from the purpose. > > > > >> > > > > >> > etc. We can then have more specific compatibles, like: > > > > >> > > > > > >> > "psci-spin-table" - holds PSCI spin tables > > > > >> > > > > > >> > so you could do: > > > > >> > > > > > >> > compatible = "runtime-code", "psci-spin-table"; > > > > >> > > > > > >> > > > > >> I understand that this binding targets firmware<->firmware rather than > > > > >> firmware<->OS, which makes it much more difficult to keep it both > > > > >> generic and sufficiently descriptive. > > > > >> > > > > >> However, I still feel that all the overlap with UEFI memory types is > > > > >> not what we want here. UEFI knows how to manage its own memory map, > > > > >> what it needs to know is what memory is already in use and for which > > > > >> exact purpose. Whether or not that implies that the memory can be > > > > >> freed at some point or can be mapped or not should follow from that. > > > > > > > > > > > > > > > Can you please make a suggestion? I am unsure what you are looking for. > > > > > > > > > > > > > I'm happy to help flesh this out, but you still have not provided us > > > > with an actual use case, so I can only draw from my own experience > > > > putting together firmware for virtual and physical ARM machines. > > > > > > I did explain that this is needed when Tianocore is on both sides of > > > the interface, since Platform Init places some things in memory and > > > the Payload needs to preserve them there, and/or know where they are. > > > > > > I think the problem might be that you don't agree with that, but it > > > seems to be a fact, so I am not sure how I can alter it. > > > > > > Please can you clearly explain which part of the use case you are missing. > > > > > > > 'Tianocore on both sides of the interface' means that Tianocore runs > > as the platform init code, and uses a bespoke DT based protocol to > > launch another instance of Tianocore as the payload, right? > > Not another instance, no. Just the other half of Tianocore. The first > half does platform init and the second half does the loading of the > OS. > That doesn't make any sense to me. > > > > Tianocore/EDK2 already implements methods to reinvoke itself if needed > > (e.g., during a firmware update), and does so by launching a new DXE > > core. So the boot sequence looks like > > > > SEC -> PEI -> DXE -> BDS -> app that invokes UpdateCapsule() -> DXE -> > > firmware update > > > > So please elaborate on how this Tianocore on both sides of the > > interface is put together when it uses this DT based handover. We > > really need a better understanding of this in order to design a DT > > binding that meets its needs. > > Are you familiar with building Tianocore as a coreboot payload, for > example? That shows Tianocore running as just the Payload, with > coreboot doing the platform init. So the use case I am talking about > is similar to that. > Yes I am familiar with that, and it is a completely different thing. As i explained before, there is already prior art for this in Tianocore, i.e., launching a Tianocore build based on a DT description of the platform, including /memory and /reserved-memory nodes. I argued that Tianocore never consumes memory reservations with UEFI semantics, given that it supplants whatever UEFI functionality the previous stage may have provided. But it shouldn't step on the code and data regions used by the previous stage if it is still running in the background (e.g., OS at EL1 and PSCI at EL2 on ARM) So this brings me back to the things I proposed in my previous reply: - memory reservations should be described in detail so the consumer knows what to do with it - memory reservations should have attributes that describe how the memory may be used if not for the described purpose I still don't see a reason for things like runtime-code and runtime-data etc based on the above. If stage N describes the memory it occupies itself as system memory, it should reserve it as well if it needs to be preserved after stage N+1 has taken over, so perhaps it should be described as a discardable memory reservation but I don't think it necessarily needs a type in that case.
On Thu, Sep 7, 2023 at 8:56 AM Simon Glass <sjg@chromium.org> wrote: > > Hi Ard, > > On Thu, 7 Sept 2023 at 07:31, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Wed, 6 Sept 2023 at 18:50, Simon Glass <sjg@chromium.org> wrote: > > > > > > Hi Ard, > > > > > > On Wed, Sep 6, 2023, 10:09 Ard Biesheuvel <ardb@kernel.org> wrote: > > >> > > >> On Wed, 6 Sept 2023 at 16:54, Simon Glass <sjg@chromium.org> wrote: > > >> > > > >> > Hi Rob, Ard, > > >> > > > >> > On Wed, 6 Sept 2023 at 08:34, Rob Herring <robh@kernel.org> wrote: > > >> > > > > >> > > On Tue, Sep 5, 2023 at 4:44 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > >> > > > > > >> > > > On Thu, 31 Aug 2023 at 01:18, Simon Glass <sjg@chromium.org> wrote: > > >> > > > > > > >> > > > > The Devicetree specification skips over handling of a logical view of > > >> > > > > the memory map, pointing users to the UEFI specification. > > >> > > > > > > >> > > > > It is common to split firmware into 'Platform Init', which does the > > >> > > > > initial hardware setup and a "Payload" which selects the OS to be booted. > > >> > > > > Thus an handover interface is required between these two pieces. > > >> > > > > > > >> > > > > Where UEFI boot-time services are not available, but UEFI firmware is > > >> > > > > present on either side of this interface, information about memory usage > > >> > > > > and attributes must be presented to the "Payload" in some form. > > >> > > > > > > >> > > > > > >> > > > I don't think the UEFI references are needed or helpful here. > > >> > > > > > >> > > > > This aims to provide an small schema addition for this mapping. > > >> > > > > > > >> > > > > For now, no attempt is made to create an exhaustive binding, so there are > > >> > > > > some example types listed. More can be added later. > > >> > > > > > > >> > > > > The compatible string is not included, since the node name is enough to > > >> > > > > indicate the purpose of a node, as per the existing reserved-memory > > >> > > > > schema. > > >> > > > > >> > > Node names reflect the 'class', but not what's specifically in the > > >> > > node. So really, all reserved-memory nodes should have the same name, > > >> > > but that ship already sailed for existing users. 'compatible' is the > > >> > > right thing here. As to what the node name should be, well, we haven't > > >> > > defined that. I think we just used 'memory' on some platforms. > > >> > > > >> > OK > > >> > > > >> > > > > >> > > > > This binding does not include a binding for the memory 'attribute' > > >> > > > > property, defined by EFI_BOOT_SERVICES.GetMemoryMap(). It may be useful > > >> > > > > to have that as well, but perhaps not as a bit mask. > > >> > > > > > > >> > > > > Signed-off-by: Simon Glass <sjg@chromium.org> > > >> > > > > --- > > >> > > > > > > >> > > > > Changes in v5: > > >> > > > > - Drop the memory-map node (should have done that in v4) > > >> > > > > - Tidy up schema a bit > > >> > > > > > > >> > > > > Changes in v4: > > >> > > > > - Make use of the reserved-memory node instead of creating a new one > > >> > > > > > > >> > > > > Changes in v3: > > >> > > > > - Reword commit message again > > >> > > > > - cc a lot more people, from the FFI patch > > >> > > > > - Split out the attributes into the /memory nodes > > >> > > > > > > >> > > > > Changes in v2: > > >> > > > > - Reword commit message > > >> > > > > > > >> > > > > .../reserved-memory/common-reserved.yaml | 53 +++++++++++++++++++ > > >> > > > > 1 file changed, 53 insertions(+) > > >> > > > > create mode 100644 dtschema/schemas/reserved-memory/common-reserved.yaml > > >> > > > > > > >> > > > > diff --git a/dtschema/schemas/reserved-memory/common-reserved.yaml b/dtschema/schemas/reserved-memory/common-reserved.yaml > > >> > > > > new file mode 100644 > > >> > > > > index 0000000..d1b466b > > >> > > > > --- /dev/null > > >> > > > > +++ b/dtschema/schemas/reserved-memory/common-reserved.yaml > > >> > > > > @@ -0,0 +1,53 @@ > > >> > > > > +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause > > >> > > > > +%YAML 1.2 > > >> > > > > +--- > > >> > > > > +$id: http://devicetree.org/schemas/reserved-memory/common-reserved.yaml# > > >> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml# > > >> > > > > + > > >> > > > > +title: Common memory reservations > > >> > > > > + > > >> > > > > +description: | > > >> > > > > + Specifies that the reserved memory region can be used for the purpose > > >> > > > > + indicated by its node name. > > >> > > > > + > > >> > > > > + Clients may reuse this reserved memory if they understand what it is for. > > >> > > > > + > > >> > > > > +maintainers: > > >> > > > > + - Simon Glass <sjg@chromium.org> > > >> > > > > + > > >> > > > > +allOf: > > >> > > > > + - $ref: reserved-memory.yaml > > >> > > > > + > > >> > > > > +properties: > > >> > > > > + $nodename: > > >> > > > > + enum: > > >> > > > > + - acpi-reclaim > > >> > > > > + - acpi-nvs > > >> > > > > + - boot-code > > >> > > > > + - boot-data > > >> > > > > + - runtime-code > > >> > > > > + - runtime-data > > >> > > > > + > > >> > > > > > >> > > > These types are used by firmware to describe the nature of certain > > >> > > > memory regions to the OS. Boot code and data can be discarded, as well > > >> > > > as ACPI reclaim after its contents have been consumed. Runtime code > > >> > > > and data need to be mapped for runtime features to work. > > >> > > > > > >> > > > When one firmware phase communicates the purpose of a certain memory > > >> > > > reservation to another, it is typically not limited to whether its > > >> > > > needs to be preserved and when it needs to be mapped (and with which > > >> > > > attributes). I'd expect a memory reservation appearing under this node > > >> > > > to have a clearly defined purpose, and the subsequent phases need to > > >> > > > be able to discover this information. > > >> > > > > > >> > > > For example, a communication buffer for secure<->non-secure > > >> > > > communication or a page with spin tables used by PSCI. None of the > > >> > > > proposed labels are appropriate for this, and I'd much rather have a > > >> > > > compatible string or some other property that clarifies the nature in > > >> > > > a more suitable way. Note that 'no-map' already exists to indicate > > >> > > > that the CPU should not map this memory unless it does so for the > > >> > > > specific purpose that the reservation was made for. > > >> > > > > >> > > I agree. I think compatible is the better approach. Some property like > > >> > > 'discard' may not be sufficient information if the OS needs to consume > > >> > > the region first and then discard it. Better to state exactly what's > > >> > > there and then the OS can imply the rest. > > >> > > > >> > OK, so what sort of compatible strings? > > >> > > > >> > How about: > > >> > "acpi-reclaim" - holds ACPI tables; memory can be reclaimed once the > > >> > tables are read and no-longer needed > > >> > > >> ACPI reclaim is a policy, not a purpose. This memory could contain > > >> many different things. > > >> > > >> > "boot-code" - holds boot code; memory can be reclaimed once the boot > > >> > phase is complete > > >> > "runtime-code" - holds runtime code; memory can be reclaimed only if > > >> > this code will not be used from that point > > >> > > > >> > > >> These are also policies. They can be inferred from the purpose. > > >> > > >> > etc. We can then have more specific compatibles, like: > > >> > > > >> > "psci-spin-table" - holds PSCI spin tables > > >> > > > >> > so you could do: > > >> > > > >> > compatible = "runtime-code", "psci-spin-table"; > > >> > > > >> > > >> I understand that this binding targets firmware<->firmware rather than > > >> firmware<->OS, which makes it much more difficult to keep it both > > >> generic and sufficiently descriptive. > > >> > > >> However, I still feel that all the overlap with UEFI memory types is > > >> not what we want here. UEFI knows how to manage its own memory map, > > >> what it needs to know is what memory is already in use and for which > > >> exact purpose. Whether or not that implies that the memory can be > > >> freed at some point or can be mapped or not should follow from that. > > > > > > > > > Can you please make a suggestion? I am unsure what you are looking for. > > > > > > > I'm happy to help flesh this out, but you still have not provided us > > with an actual use case, so I can only draw from my own experience > > putting together firmware for virtual and physical ARM machines. > > I did explain that this is needed when Tianocore is on both sides of > the interface, since Platform Init places some things in memory and > the Payload needs to preserve them there, and/or know where they are. > > I think the problem might be that you don't agree with that, but it > seems to be a fact, so I am not sure how I can alter it. > > Please can you clearly explain which part of the use case you are missing. > > > > > All the ACPI and UEFI lingo needs to be dropped. This is relevant only > > to the OS, and only if the prior stage exposes UEFI interfaces, in > > which case it does not need this binding. > > OK I can drop those from the commit message. > > > > > So on one side, there is the requirement for each memory reservation > > to be described with sufficient detail so that a subsequent boot stage > > (firmware or OS) can use it for its intended purpose, provided that > > this boot stage is aware of its purpose (i.e., it has a driver that > > matches on the compatible string in question, and actually maps/uses > > the memory) > > > > On the other side, we need to describe how a memory reservation should > > be treated if the boot stage doesn't know its purpose, has no interest > > in using it or has consumed the contents and has no longer a need for > > the region. We already have no-map to describe that the memory should > > never be mapped (and this may be disregarded by an actual driver for > > the region). I imagine we might add 'discardable' as a boolean DT > > property, meaning that stage N may use the memory whichever way it > > wants if it is not going to use it for its intended purpose, provided > > that it deletes the node from the DT before passing it on to stage > > N+1. > > OK. For now I think that everything is discardable, so long as the > Payload knows the purpose and that it not needed. That is what Rob > seemed to be saying. If we add 'discardable', does that mean that > things default to non-discardable? Would that not be a change of > behaviour for existing users? I believe I said "discardable" should be implied from the compatible, not be a discreet property. It is possible that some region is passed thru to multiple stages and is only discardable by the last stage (or next to last or...). So discardable depends on the consumer. There has to be some logic of "I know what this foo-bar region is for and know it isn't needed". If the consumer doesn't know what the region is, then it must default to leaving it reserved. > > One thing that needs to be clarified is how this binding interacts > > with /memory nodes. I assume that currently, /reserved-memory is > > independent, i.e., it could describe mappable memory that is not > > covered by /memory at all. If this is the case, we have to decide > > whether or not discardable regions can be treated in the same way, or > > whether we should require that discardable regions are covered by > > /memory. > > I would expect all memory to be described in /memory nodes. What is > the use case for omitting it? That is the expectation though nothing prevents a platform from omitting areas. Most likely only the beginning or end of memory. System partitioning usecases likely just describe each partition's portion of memory. I don't recall ever seeing a bunch of memory regions rather than 1-2 with reserved-memory nodes. Also, I don't think we prevent a reserved region outside the memory region(s) though I imagine (at least Linux) just ignores them. > Are you thinking of SRAM, etc? We have mmio-sram binding for that which has its own way to carve up the regions. Rob
On Thu, 7 Sept 2023 at 17:57, Simon Glass <sjg@chromium.org> wrote: > > Hi Ard, > > On Thu, 7 Sept 2023 at 09:07, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Thu, 7 Sept 2023 at 16:50, Simon Glass <sjg@chromium.org> wrote: > > > > > > Hi Ard, > > > > > > On Thu, 7 Sept 2023 at 08:12, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > > > On Thu, 7 Sept 2023 at 15:56, Simon Glass <sjg@chromium.org> wrote: > > > > > > > > > > Hi Ard, > > > > > > > > > > On Thu, 7 Sept 2023 at 07:31, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > ... > > > > > > > > > > > > I'm happy to help flesh this out, but you still have not provided us > > > > > > with an actual use case, so I can only draw from my own experience > > > > > > putting together firmware for virtual and physical ARM machines. > > > > > > > > > > I did explain that this is needed when Tianocore is on both sides of > > > > > the interface, since Platform Init places some things in memory and > > > > > the Payload needs to preserve them there, and/or know where they are. > > > > > > > > > > I think the problem might be that you don't agree with that, but it > > > > > seems to be a fact, so I am not sure how I can alter it. > > > > > > > > > > Please can you clearly explain which part of the use case you are missing. > > > > > > > > > > > > > 'Tianocore on both sides of the interface' means that Tianocore runs > > > > as the platform init code, and uses a bespoke DT based protocol to > > > > launch another instance of Tianocore as the payload, right? > > > > > > Not another instance, no. Just the other half of Tianocore. The first > > > half does platform init and the second half does the loading of the > > > OS. > > > > > > > That doesn't make any sense to me. > > > > > > > > > > Tianocore/EDK2 already implements methods to reinvoke itself if needed > > > > (e.g., during a firmware update), and does so by launching a new DXE > > > > core. So the boot sequence looks like > > > > > > > > SEC -> PEI -> DXE -> BDS -> app that invokes UpdateCapsule() -> DXE -> > > > > firmware update > > > > > > > > So please elaborate on how this Tianocore on both sides of the > > > > interface is put together when it uses this DT based handover. We > > > > really need a better understanding of this in order to design a DT > > > > binding that meets its needs. > > > > > > Are you familiar with building Tianocore as a coreboot payload, for > > > example? That shows Tianocore running as just the Payload, with > > > coreboot doing the platform init. So the use case I am talking about > > > is similar to that. > > > > > > > Yes I am familiar with that, and it is a completely different thing. > > Right, but that is my use case. > OK. You alluded to Tianocore <-> Tianocore being your use case, which is why I kept asking for clarification, as using a DT with this binding seems unusual at the very least. So coreboot does the platform init, and then hands over to Tianocore. I take it we are not talking about x86 here, so there are no Intel FSP blobs that may have dependencies on Tianocore/EDK2 pieces, right? So there are no UEFI semantics in the memory descriptions that coreboot provides to Tianocore. So coreboot provides information to TIanocore about - the platform topology (DT as usual) - DRAM memory banks - memory reservations - secure firmware services perhaps? - anything else? > > > > As i explained before, there is already prior art for this in > > Tianocore, i.e., launching a Tianocore build based on a DT description > > of the platform, including /memory and /reserved-memory nodes. > > By prior art do you mean code, or an existing binding? In either case, > can you please point me to it? Is this a generic binding used on x86 > as well, or just for ARM? > > My goal here is to augment the binding. > No I mean code. There is https://github.com/tianocore/edk2/tree/master/EmbeddedPkg/Drivers/FdtClientDxe which encapsulates the DT received from the previous boot stage, and exposes it as a DXE protocol. There are other drivers that depend on this protocol, e.g., to discover additional memory nodes, virtio-mmio drivers and PCI host bridges. https://github.com/tianocore/edk2/tree/master/OvmfPkg/Fdt The bindings used are the ones documented in the Linux kernel tree - no ad-hoc bindings are being used as far as I know. But the point I was making before re prior art was really about using existing bindings rather than inventing new ones. Since we are now talking about augmenting /reserved-memory, I think we're already on the same page in this regard (with the caveat that the EDK2 code does not actually honour /reserved-memory at this point, but this is because none of the platforms it is being used on today uses that node) > > > > I argued that Tianocore never consumes memory reservations with UEFI > > semantics, given that it supplants whatever UEFI functionality the > > previous stage may have provided. But it shouldn't step on the code > > and data regions used by the previous stage if it is still running in > > the background (e.g., OS at EL1 and PSCI at EL2 on ARM) > > > > So this brings me back to the things I proposed in my previous reply: > > - memory reservations should be described in detail so the consumer > > knows what to do with it > > Yes I can add more detail, if that is all that is needed. But we seem > to still not be aligned on the goal. > > I do think we're converging, actually - it is just taking me some time to get a clear mental picture of how this will be used. > > - memory reservations should have attributes that describe how the > > memory may be used if not for the described purpose > > > > I still don't see a reason for things like runtime-code and > > runtime-data etc based on the above. If stage N describes the memory > > it occupies itself as system memory, it should reserve it as well if > > it needs to be preserved after stage N+1 has taken over, so perhaps it > > should be described as a discardable memory reservation but I don't > > think it necessarily needs a type in that case. > > Well if you can find another way to do this in the DT, that is fine. > It will all be under /reserved-memory, as far as I understand. We just need to get to the right level of abstraction.
Hi Ard, On Thu, 7 Sept 2023 at 10:19, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Thu, 7 Sept 2023 at 17:57, Simon Glass <sjg@chromium.org> wrote: > > > > Hi Ard, > > > > On Thu, 7 Sept 2023 at 09:07, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > On Thu, 7 Sept 2023 at 16:50, Simon Glass <sjg@chromium.org> wrote: > > > > > > > > Hi Ard, > > > > > > > > On Thu, 7 Sept 2023 at 08:12, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > > > > > On Thu, 7 Sept 2023 at 15:56, Simon Glass <sjg@chromium.org> wrote: > > > > > > > > > > > > Hi Ard, > > > > > > > > > > > > On Thu, 7 Sept 2023 at 07:31, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > > > ... > > > > > > > > > > > > > > I'm happy to help flesh this out, but you still have not provided us > > > > > > > with an actual use case, so I can only draw from my own experience > > > > > > > putting together firmware for virtual and physical ARM machines. > > > > > > > > > > > > I did explain that this is needed when Tianocore is on both sides of > > > > > > the interface, since Platform Init places some things in memory and > > > > > > the Payload needs to preserve them there, and/or know where they are. > > > > > > > > > > > > I think the problem might be that you don't agree with that, but it > > > > > > seems to be a fact, so I am not sure how I can alter it. > > > > > > > > > > > > Please can you clearly explain which part of the use case you are missing. > > > > > > > > > > > > > > > > 'Tianocore on both sides of the interface' means that Tianocore runs > > > > > as the platform init code, and uses a bespoke DT based protocol to > > > > > launch another instance of Tianocore as the payload, right? > > > > > > > > Not another instance, no. Just the other half of Tianocore. The first > > > > half does platform init and the second half does the loading of the > > > > OS. > > > > > > > > > > That doesn't make any sense to me. > > > > > > > > > > > > > Tianocore/EDK2 already implements methods to reinvoke itself if needed > > > > > (e.g., during a firmware update), and does so by launching a new DXE > > > > > core. So the boot sequence looks like > > > > > > > > > > SEC -> PEI -> DXE -> BDS -> app that invokes UpdateCapsule() -> DXE -> > > > > > firmware update > > > > > > > > > > So please elaborate on how this Tianocore on both sides of the > > > > > interface is put together when it uses this DT based handover. We > > > > > really need a better understanding of this in order to design a DT > > > > > binding that meets its needs. > > > > > > > > Are you familiar with building Tianocore as a coreboot payload, for > > > > example? That shows Tianocore running as just the Payload, with > > > > coreboot doing the platform init. So the use case I am talking about > > > > is similar to that. > > > > > > > > > > Yes I am familiar with that, and it is a completely different thing. > > > > Right, but that is my use case. > > > > OK. You alluded to Tianocore <-> Tianocore being your use case, which > is why I kept asking for clarification, as using a DT with this > binding seems unusual at the very least. Nevertheless, that is the goal. > > So coreboot does the platform init, and then hands over to Tianocore. > > I take it we are not talking about x86 here, so there are no Intel FSP > blobs that may have dependencies on Tianocore/EDK2 pieces, right? So > there are no UEFI semantics in the memory descriptions that coreboot > provides to Tianocore. > > So coreboot provides information to TIanocore about > - the platform topology (DT as usual) > - DRAM memory banks > - memory reservations > - secure firmware services perhaps? > - anything else? Please don't widen the discussion as we are having enough trouble as it is. Let's focus on the memory reservations. > > > > > > > > As i explained before, there is already prior art for this in > > > Tianocore, i.e., launching a Tianocore build based on a DT description > > > of the platform, including /memory and /reserved-memory nodes. > > > > By prior art do you mean code, or an existing binding? In either case, > > can you please point me to it? Is this a generic binding used on x86 > > as well, or just for ARM? > > > > My goal here is to augment the binding. > > > > No I mean code. > > There is > > https://github.com/tianocore/edk2/tree/master/EmbeddedPkg/Drivers/FdtClientDxe > > which encapsulates the DT received from the previous boot stage, and > exposes it as a DXE protocol. > > There are other drivers that depend on this protocol, e.g., to > discover additional memory nodes, virtio-mmio drivers and PCI host > bridges. > > https://github.com/tianocore/edk2/tree/master/OvmfPkg/Fdt That looks like Tianocore internals rather than a binding, so far as I can tell. I do need a binding. > > The bindings used are the ones documented in the Linux kernel tree - > no ad-hoc bindings are being used as far as I know. > > But the point I was making before re prior art was really about using > existing bindings rather than inventing new ones. Since we are now > talking about augmenting /reserved-memory, I think we're already on > the same page in this regard (with the caveat that the EDK2 code does > not actually honour /reserved-memory at this point, but this is > because none of the platforms it is being used on today uses that > node) OK I'll try that patch again with compatible strings instead of node names[1] > > > > > > > I argued that Tianocore never consumes memory reservations with UEFI > > > semantics, given that it supplants whatever UEFI functionality the > > > previous stage may have provided. But it shouldn't step on the code > > > and data regions used by the previous stage if it is still running in > > > the background (e.g., OS at EL1 and PSCI at EL2 on ARM) > > > > > > So this brings me back to the things I proposed in my previous reply: > > > - memory reservations should be described in detail so the consumer > > > knows what to do with it > > > > Yes I can add more detail, if that is all that is needed. But we seem > > to still not be aligned on the goal. > > > > > > I do think we're converging, actually - it is just taking me some time > to get a clear mental picture of how this will be used. > > > > - memory reservations should have attributes that describe how the > > > memory may be used if not for the described purpose > > > > > > I still don't see a reason for things like runtime-code and > > > runtime-data etc based on the above. If stage N describes the memory > > > it occupies itself as system memory, it should reserve it as well if > > > it needs to be preserved after stage N+1 has taken over, so perhaps it > > > should be described as a discardable memory reservation but I don't > > > think it necessarily needs a type in that case. > > > > Well if you can find another way to do this in the DT, that is fine. > > > > It will all be under /reserved-memory, as far as I understand. We just > need to get to the right level of abstraction. OK I'll try again. Regards, Simon [1] I was led down the node-name path by this text in the DT spec "Following the generic-names recommended practice, node names should reflect the purpose of the node (ie. “framebuffer” or “dma-pool”). Unit address (@<address>) should be appended to the name if the node is a static allocation."
diff --git a/dtschema/schemas/reserved-memory/common-reserved.yaml b/dtschema/schemas/reserved-memory/common-reserved.yaml new file mode 100644 index 0000000..d1b466b --- /dev/null +++ b/dtschema/schemas/reserved-memory/common-reserved.yaml @@ -0,0 +1,53 @@ +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/reserved-memory/common-reserved.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Common memory reservations + +description: | + Specifies that the reserved memory region can be used for the purpose + indicated by its node name. + + Clients may reuse this reserved memory if they understand what it is for. + +maintainers: + - Simon Glass <sjg@chromium.org> + +allOf: + - $ref: reserved-memory.yaml + +properties: + $nodename: + enum: + - acpi-reclaim + - acpi-nvs + - boot-code + - boot-data + - runtime-code + - runtime-data + + reg: + description: region of memory that is reserved for the purpose indicated + by the node name. + +required: + - reg + +unevaluatedProperties: false + +examples: + - | + reserved-memory { + #address-cells = <1>; + #size-cells = <1>; + + boot-code@12340000 { + reg = <0x12340000 0x00800000>; + }; + + boot-data@43210000 { + reg = <0x43210000 0x00800000>; + }; + };
The Devicetree specification skips over handling of a logical view of the memory map, pointing users to the UEFI specification. It is common to split firmware into 'Platform Init', which does the initial hardware setup and a "Payload" which selects the OS to be booted. Thus an handover interface is required between these two pieces. Where UEFI boot-time services are not available, but UEFI firmware is present on either side of this interface, information about memory usage and attributes must be presented to the "Payload" in some form. This aims to provide an small schema addition for this mapping. For now, no attempt is made to create an exhaustive binding, so there are some example types listed. More can be added later. The compatible string is not included, since the node name is enough to indicate the purpose of a node, as per the existing reserved-memory schema. This binding does not include a binding for the memory 'attribute' property, defined by EFI_BOOT_SERVICES.GetMemoryMap(). It may be useful to have that as well, but perhaps not as a bit mask. Signed-off-by: Simon Glass <sjg@chromium.org> --- Changes in v5: - Drop the memory-map node (should have done that in v4) - Tidy up schema a bit Changes in v4: - Make use of the reserved-memory node instead of creating a new one Changes in v3: - Reword commit message again - cc a lot more people, from the FFI patch - Split out the attributes into the /memory nodes Changes in v2: - Reword commit message .../reserved-memory/common-reserved.yaml | 53 +++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100644 dtschema/schemas/reserved-memory/common-reserved.yaml