diff mbox series

[v4,3/3] PCI/ACPI: negotiate CXL _OSC

Message ID 20220331202022.1823174-4-vishal.l.verma@intel.com
State Superseded
Headers show
Series PCI/ACPI: add support for CXL _OSC | expand

Commit Message

Vishal Verma March 31, 2022, 8:20 p.m. UTC
Add full support for negotiating _OSC as defined in the CXL 2.0 spec, as
applicable to CXL-enabled platforms. Advertise support for the CXL
features we support - 'CXL 2.0 port/device register access', 'Protocol
Error Reporting', and 'CXL Native Hot Plug'. Request control for 'CXL
Memory Error Reporting'. The requests are dependent on CONFIG_* based
prerequisites, and prior PCI enabling, similar to how the standard PCI
_OSC bits are determined.

The CXL specification does not define any additional constraints on
the hotplug flow beyond PCIe native hotplug, so a kernel that supports
native PCIe hotplug, supports CXL hotplug. For error handling protocol
and link errors just use PCIe AER. There is nascent support for
amending AER events with CXL specific status [1], but there's
otherwise no additional OS responsibility for CXL errors beyond PCIe
AER. CXL Memory Errors behave the same as typical memory errors so
CONFIG_MEMORY_FAILURE is sufficient to indicate support to platform
firmware.

[1]: https://lore.kernel.org/linux-cxl/164740402242.3912056.8303625392871313860.stgit@dwillia2-desk3.amr.corp.intel.com/

Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Robert Moore <robert.moore@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 include/linux/acpi.h    |  28 +++++++-
 include/acpi/acpi_bus.h |   6 +-
 drivers/acpi/pci_root.c | 145 ++++++++++++++++++++++++++++++++++------
 3 files changed, 157 insertions(+), 22 deletions(-)

Comments

Davidlohr Bueso April 1, 2022, 8:40 p.m. UTC | #1
On Thu, 31 Mar 2022, Vishal Verma wrote:

>The CXL specification does not define any additional constraints on
>the hotplug flow beyond PCIe native hotplug, so a kernel that supports
>native PCIe hotplug, supports CXL hotplug.

Hmm but from a Linux-pov does it make sense to allow hotplug
support if the MM cannot handle it?

@@ -531,7 +518,8 @@ static u32 calculate_cxl_support(void)
	support = OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT;
	if (pci_aer_available())
		support |= OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT;
-       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
+       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE) &&
+           IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
		support |= OSC_CXL_NATIVE_HP_SUPPORT;

	return support;

After all, per the CXL 2.0 Type 3 device Hot-Add flow:

""
7. CXL aware software notifies OS memory manager about the new memory and its
attributes such as latency and bandwidth. Memory manager processes a request
and adds the new memory to its allocation pool.
""

Thanks,
Davidlohr
Dan Williams April 1, 2022, 9:34 p.m. UTC | #2
On Fri, Apr 1, 2022 at 1:40 PM Davidlohr Bueso <dave@stgolabs.net> wrote:
>
> On Thu, 31 Mar 2022, Vishal Verma wrote:
>
> >The CXL specification does not define any additional constraints on
> >the hotplug flow beyond PCIe native hotplug, so a kernel that supports
> >native PCIe hotplug, supports CXL hotplug.
>
> Hmm but from a Linux-pov does it make sense to allow hotplug
> support if the MM cannot handle it?

I would say yes, i.e. do not consider CONFIG_MEMORY_HOTPLUG for
OSC_CXL_NATIVE_HP_SUPPORT, but see below and poke holes in my
argument...

>
> @@ -531,7 +518,8 @@ static u32 calculate_cxl_support(void)
>         support = OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT;
>         if (pci_aer_available())
>                 support |= OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT;
> -       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
> +       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE) &&
> +           IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>                 support |= OSC_CXL_NATIVE_HP_SUPPORT;
>
>         return support;
>
> After all, per the CXL 2.0 Type 3 device Hot-Add flow:
>
> ""
> 7. CXL aware software notifies OS memory manager about the new memory and its
> attributes such as latency and bandwidth. Memory manager processes a request
> and adds the new memory to its allocation pool.
> ""

If I look at ACPI hotplug it is true that CONFIG_ACPI_HOTPLUG_MEMORY
depends on CONFIG_MEMORY_HOTPLUG. However, it is also true that there
is no existing _OSC for memory hotplug support. The reason is that
ACPI memory hotplug requires the OS to acknowledge / coordinate with
memory plug events via a scan handler. On the CXL side the equivalent
would be if Linux supported the Mechanical Retention Lock [1], or
otherwise had some coordination for the driver of a PCI device
undergoing hotplug to be consulted on whether the hotplug should
proceed or not.

The concern is that if Linux says no to supporting CXL hotplug then
the BIOS may say no to giving the OS hotplug control of any other PCIe
device. So the question here is not whether hotplug is enabled, it's
whether it is handled natively by the at all OS, and if
CONFIG_HOTPLUG_PCI_PCIE is enabled then the answer is "yes".

Otherwise, the plan for CXL coordinated remove, since the kernel does
not support blocking hotplug, is to require the memory device to be
disabled before hotplug is attempted. When CONFIG_MEMORY_HOTPLUG is
disabled that step will fail and the remove attempt cancelled. by the
user. If that is not honored and the card is removed anyway then it
does not matter if CONFIG_MEMORY_HOTPLUG is enabled or not, it will
cause a crash and other badness.

Long story short, just say yes, to CXL hotplug and require removal to
be coordinated by userspace unless and until the kernel grows better
mechanisms for doing "managed" removal of devices in consultation with
the driver.

[1]: https://lore.kernel.org/all/20201122014203.4706-1-ashok.raj@intel.com/
Davidlohr Bueso April 4, 2022, 8:30 p.m. UTC | #3
On Fri, 01 Apr 2022, Dan Williams wrote:

>On Fri, Apr 1, 2022 at 1:40 PM Davidlohr Bueso <dave@stgolabs.net> wrote:
>>
>> On Thu, 31 Mar 2022, Vishal Verma wrote:
>>
>> >The CXL specification does not define any additional constraints on
>> >the hotplug flow beyond PCIe native hotplug, so a kernel that supports
>> >native PCIe hotplug, supports CXL hotplug.
>>
>> Hmm but from a Linux-pov does it make sense to allow hotplug
>> support if the MM cannot handle it?
>
>I would say yes, i.e. do not consider CONFIG_MEMORY_HOTPLUG for
>OSC_CXL_NATIVE_HP_SUPPORT, but see below and poke holes in my
>argument...
>
>>
>> @@ -531,7 +518,8 @@ static u32 calculate_cxl_support(void)
>>         support = OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT;
>>         if (pci_aer_available())
>>                 support |= OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT;
>> -       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
>> +       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE) &&
>> +           IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>>                 support |= OSC_CXL_NATIVE_HP_SUPPORT;
>>
>>         return support;
>>
>> After all, per the CXL 2.0 Type 3 device Hot-Add flow:
>>
>> ""
>> 7. CXL aware software notifies OS memory manager about the new memory and its
>> attributes such as latency and bandwidth. Memory manager processes a request
>> and adds the new memory to its allocation pool.
>> ""
>
>If I look at ACPI hotplug it is true that CONFIG_ACPI_HOTPLUG_MEMORY
>depends on CONFIG_MEMORY_HOTPLUG. However, it is also true that there
>is no existing _OSC for memory hotplug support. The reason is that
>ACPI memory hotplug requires the OS to acknowledge / coordinate with
>memory plug events via a scan handler. On the CXL side the equivalent
>would be if Linux supported the Mechanical Retention Lock [1], or
>otherwise had some coordination for the driver of a PCI device
>undergoing hotplug to be consulted on whether the hotplug should
>proceed or not.
>
>The concern is that if Linux says no to supporting CXL hotplug then
>the BIOS may say no to giving the OS hotplug control of any other PCIe
>device. So the question here is not whether hotplug is enabled, it's
>whether it is handled natively by the at all OS, and if
>CONFIG_HOTPLUG_PCI_PCIE is enabled then the answer is "yes".
>
>Otherwise, the plan for CXL coordinated remove, since the kernel does
>not support blocking hotplug, is to require the memory device to be
>disabled before hotplug is attempted. When CONFIG_MEMORY_HOTPLUG is
>disabled that step will fail and the remove attempt cancelled. by the
>user. If that is not honored and the card is removed anyway then it
>does not matter if CONFIG_MEMORY_HOTPLUG is enabled or not, it will
>cause a crash and other badness.
>
>Long story short, just say yes, to CXL hotplug and require removal to
>be coordinated by userspace unless and until the kernel grows better
>mechanisms for doing "managed" removal of devices in consultation with
>the driver.

+Cc Adam.

Thank you for the overview of the landscape; I was assuming this last
part already existed. I would only suggest documenting the above in
calculate_cxl_support(), such that future readers don't also wonder
about this and why CXL doesn't follow what CONFIG_ACPI_HOTPLUG_MEMORY
does.

Thanks,
Davidlohr

>
>[1]: https://lore.kernel.org/all/20201122014203.4706-1-ashok.raj@intel.com/
Rafael J. Wysocki April 5, 2022, 2 p.m. UTC | #4
On Thu, Mar 31, 2022 at 10:20 PM Vishal Verma <vishal.l.verma@intel.com> wrote:
>
> Add full support for negotiating _OSC as defined in the CXL 2.0 spec, as
> applicable to CXL-enabled platforms. Advertise support for the CXL
> features we support - 'CXL 2.0 port/device register access', 'Protocol
> Error Reporting', and 'CXL Native Hot Plug'. Request control for 'CXL
> Memory Error Reporting'. The requests are dependent on CONFIG_* based
> prerequisites, and prior PCI enabling, similar to how the standard PCI
> _OSC bits are determined.
>
> The CXL specification does not define any additional constraints on
> the hotplug flow beyond PCIe native hotplug, so a kernel that supports
> native PCIe hotplug, supports CXL hotplug. For error handling protocol
> and link errors just use PCIe AER. There is nascent support for
> amending AER events with CXL specific status [1], but there's
> otherwise no additional OS responsibility for CXL errors beyond PCIe
> AER. CXL Memory Errors behave the same as typical memory errors so
> CONFIG_MEMORY_FAILURE is sufficient to indicate support to platform
> firmware.
>
> [1]: https://lore.kernel.org/linux-cxl/164740402242.3912056.8303625392871313860.stgit@dwillia2-desk3.amr.corp.intel.com/
>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Robert Moore <robert.moore@intel.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
>  include/linux/acpi.h    |  28 +++++++-
>  include/acpi/acpi_bus.h |   6 +-
>  drivers/acpi/pci_root.c | 145 ++++++++++++++++++++++++++++++++++------
>  3 files changed, 157 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index fc40da914315..cf360b9642d9 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -554,10 +554,15 @@ acpi_status acpi_run_osc(acpi_handle handle, struct acpi_osc_context *context);
>  #define OSC_PCI_CAPABILITY_DWORDS              3
>  #define OSC_CXL_CAPABILITY_DWORDS              5
>
> -/* Indexes into _OSC Capabilities Buffer (DWORDs 2 & 3 are device-specific) */
> +/*
> + * Indexes into _OSC Capabilities Buffer
> + * DWORDs 2 & 3 are device-specific, and 4 & 5 are specific to CXL platforms

Say "DWORDs 2 through 5 are device-specific" and you don't need to
mention CXL here.

> + */
>  #define OSC_QUERY_DWORD                                0       /* DWORD 1 */
>  #define OSC_SUPPORT_DWORD                      1       /* DWORD 2 */
>  #define OSC_CONTROL_DWORD                      2       /* DWORD 3 */
> +#define OSC_CXL_SUPPORT_DWORD                  3       /* DWORD 4 */
> +#define OSC_CXL_CONTROL_DWORD                  4       /* DWORD 5 */

I would rename the last two symbols as OSC_EXT_SUPPORT_DWORD and
OSC_EXT_CONTROL_DWORD (see below for an explanation).

>
>  /* _OSC Capabilities DWORD 1: Query/Control and Error Returns (generic) */
>  #define OSC_QUERY_ENABLE                       0x00000001  /* input */
> @@ -611,6 +616,15 @@ extern u32 osc_sb_native_usb4_control;
>  #define OSC_PCI_EXPRESS_LTR_CONTROL            0x00000020
>  #define OSC_PCI_EXPRESS_DPC_CONTROL            0x00000080
>
> +/* CXL _OSC: Capabilities DWORD 4: Support Field */
> +#define OSC_CXL_1_1_PORT_REG_ACCESS_SUPPORT    0x00000001
> +#define OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT        0x00000002
> +#define OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT 0x00000004
> +#define OSC_CXL_NATIVE_HP_SUPPORT              0x00000008
> +
> +/* CXL _OSC: Capabilities DWORD 5: Control Field */
> +#define OSC_CXL_ERROR_REPORTING_CONTROL                0x00000001
> +
>  static inline u32 acpi_osc_ctx_get_pci_control(struct acpi_osc_context *context)
>  {
>         u32 *ret = context->ret.pointer;
> @@ -618,6 +632,13 @@ static inline u32 acpi_osc_ctx_get_pci_control(struct acpi_osc_context *context)
>         return ret[OSC_CONTROL_DWORD];
>  }
>
> +static inline u32 acpi_osc_ctx_get_cxl_control(struct acpi_osc_context *context)
> +{
> +       u32 *ret = context->ret.pointer;
> +
> +       return ret[OSC_CXL_CONTROL_DWORD];
> +}
> +
>  #define ACPI_GSB_ACCESS_ATTRIB_QUICK           0x00000002
>  #define ACPI_GSB_ACCESS_ATTRIB_SEND_RCV         0x00000004
>  #define ACPI_GSB_ACCESS_ATTRIB_BYTE            0x00000006
> @@ -1020,6 +1041,11 @@ static inline u32 acpi_osc_ctx_get_pci_control(struct acpi_osc_context *context)
>         return 0;
>  }
>
> +static inline u32 acpi_osc_ctx_get_cxl_control(struct acpi_osc_context *context)
> +{
> +       return 0;
> +}
> +
>  #endif /* !CONFIG_ACPI */
>
>  #ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 9413d2389711..0fdd913c1fd7 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -593,8 +593,10 @@ struct acpi_pci_root {
>         int bridge_type;
>         struct resource secondary;      /* downstream bus range */
>
> -       u32 osc_support_set;    /* _OSC state of support bits */
> -       u32 osc_control_set;    /* _OSC state of control bits */
> +       u32 osc_support_set;            /* _OSC state of support bits */
> +       u32 osc_control_set;            /* _OSC state of control bits */
> +       u32 cxl_osc_support_set;        /* _OSC state of CXL support bits */
> +       u32 cxl_osc_control_set;        /* _OSC state of CXL control bits */

Well, could these two be renamed to osc_ext_support_set and
osc_ext_controle_set ("ext" for "extended"), respectively?

At the acpi_bus.h level, CXL is irrelevant and expecting all of the
prospective readers of it to find out what CXL means seems a bit
excessive.

Otherwise, the changes in this patch look reasonable to me.

>         phys_addr_t mcfg_addr;
>  };
>
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 5d33bc61fe44..a2e74db28e30 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -142,6 +142,17 @@ static struct pci_osc_bit_struct pci_osc_control_bit[] = {
>         { OSC_PCI_EXPRESS_DPC_CONTROL, "DPC" },
>  };
>
> +static struct pci_osc_bit_struct cxl_osc_support_bit[] = {
> +       { OSC_CXL_1_1_PORT_REG_ACCESS_SUPPORT, "CXL11PortRegAccess" },
> +       { OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT, "CXL20PortDevRegAccess" },
> +       { OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT, "CXLProtocolErrorReporting" },
> +       { OSC_CXL_NATIVE_HP_SUPPORT, "CXLNativeHotPlug" },
> +};
> +
> +static struct pci_osc_bit_struct cxl_osc_control_bit[] = {
> +       { OSC_CXL_ERROR_REPORTING_CONTROL, "CXLMemErrorReporting" },
> +};
> +
>  static void decode_osc_bits(struct acpi_pci_root *root, char *msg, u32 word,
>                             struct pci_osc_bit_struct *table, int size)
>  {
> @@ -170,6 +181,18 @@ static void decode_osc_control(struct acpi_pci_root *root, char *msg, u32 word)
>                         ARRAY_SIZE(pci_osc_control_bit));
>  }
>
> +static void decode_cxl_osc_support(struct acpi_pci_root *root, char *msg, u32 word)
> +{
> +       decode_osc_bits(root, msg, word, cxl_osc_support_bit,
> +                       ARRAY_SIZE(cxl_osc_support_bit));
> +}
> +
> +static void decode_cxl_osc_control(struct acpi_pci_root *root, char *msg, u32 word)
> +{
> +       decode_osc_bits(root, msg, word, cxl_osc_control_bit,
> +                       ARRAY_SIZE(cxl_osc_control_bit));
> +}
> +
>  static inline bool is_pcie(struct acpi_pci_root *root)
>  {
>         return root->bridge_type == ACPI_BRIDGE_TYPE_PCIE;
> @@ -198,7 +221,8 @@ static int cap_length(struct acpi_pci_root *root)
>  }
>
>  static acpi_status acpi_pci_run_osc(struct acpi_pci_root *root,
> -                                   const u32 *capbuf, u32 *retval)
> +                                   const u32 *capbuf, u32 *pci_control,
> +                                   u32 *cxl_control)
>  {
>         struct acpi_osc_context context = {
>                 .uuid_str = to_uuid(root),
> @@ -210,18 +234,20 @@ static acpi_status acpi_pci_run_osc(struct acpi_pci_root *root,
>
>         status = acpi_run_osc(root->device->handle, &context);
>         if (ACPI_SUCCESS(status)) {
> -               *retval = acpi_osc_ctx_get_pci_control(&context);
> +               *pci_control = acpi_osc_ctx_get_pci_control(&context);
> +               if (is_cxl(root))
> +                       *cxl_control = acpi_osc_ctx_get_cxl_control(&context);
>                 kfree(context.ret.pointer);
>         }
>         return status;
>  }
>
> -static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root,
> -                                       u32 support,
> -                                       u32 *control)
> +static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root, u32 support,
> +                                     u32 *control, u32 cxl_support,
> +                                     u32 *cxl_control)
>  {
>         acpi_status status;
> -       u32 result, capbuf[OSC_CXL_CAPABILITY_DWORDS];
> +       u32 pci_result, cxl_result, capbuf[OSC_CXL_CAPABILITY_DWORDS];
>
>         support |= root->osc_support_set;
>
> @@ -229,11 +255,21 @@ static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root,
>         capbuf[OSC_SUPPORT_DWORD] = support;
>         capbuf[OSC_CONTROL_DWORD] = *control | root->osc_control_set;
>
> +       if (is_cxl(root)) {
> +               cxl_support |= root->cxl_osc_support_set;
> +               capbuf[OSC_CXL_SUPPORT_DWORD] = cxl_support;
> +               capbuf[OSC_CXL_CONTROL_DWORD] = *cxl_control | root->cxl_osc_control_set;
> +       }
> +
>  retry:
> -       status = acpi_pci_run_osc(root, capbuf, &result);
> +       status = acpi_pci_run_osc(root, capbuf, &pci_result, &cxl_result);
>         if (ACPI_SUCCESS(status)) {
>                 root->osc_support_set = support;
> -               *control = result;
> +               *control = pci_result;
> +               if (is_cxl(root)) {
> +                       root->cxl_osc_support_set = cxl_support;
> +                       *cxl_control = cxl_result;
> +               }
>         } else if (is_cxl(root)) {
>                 /*
>                  * CXL _OSC is optional on CXL 1.1 hosts. Fall back to PCIe _OSC
> @@ -356,6 +392,8 @@ EXPORT_SYMBOL_GPL(acpi_get_pci_dev);
>   * @handle: ACPI handle of a PCI root bridge (or PCIe Root Complex).
>   * @mask: Mask of _OSC bits to request control of, place to store control mask.
>   * @support: _OSC supported capability.
> + * @cxl_mask: Mask of CXL _OSC control bits, place to store control mask.
> + * @cxl_support: CXL _OSC supported capability.
>   *
>   * Run _OSC query for @mask and if that is successful, compare the returned
>   * mask of control bits with @req.  If all of the @req bits are set in the
> @@ -366,12 +404,14 @@ EXPORT_SYMBOL_GPL(acpi_get_pci_dev);
>   * _OSC bits the BIOS has granted control of, but its contents are meaningless
>   * on failure.
>   **/
> -static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 support)
> +static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask,
> +                                           u32 support, u32 *cxl_mask,
> +                                           u32 cxl_support)
>  {
>         u32 req = OSC_PCI_EXPRESS_CAPABILITY_CONTROL;
>         struct acpi_pci_root *root;
>         acpi_status status;
> -       u32 ctrl, capbuf[OSC_CXL_CAPABILITY_DWORDS];
> +       u32 ctrl, cxl_ctrl = 0, capbuf[OSC_CXL_CAPABILITY_DWORDS];
>
>         if (!mask)
>                 return AE_BAD_PARAMETER;
> @@ -383,20 +423,42 @@ static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 s
>         ctrl   = *mask;
>         *mask |= root->osc_control_set;
>
> +       if (is_cxl(root)) {
> +               cxl_ctrl = *cxl_mask;
> +               *cxl_mask |= root->cxl_osc_control_set;
> +       }
> +
>         /* Need to check the available controls bits before requesting them. */
>         do {
> -               status = acpi_pci_query_osc(root, support, mask);
> +               u32 pci_missing = 0, cxl_missing = 0;
> +
> +               status = acpi_pci_query_osc(root, support, mask, cxl_support,
> +                                           cxl_mask);
>                 if (ACPI_FAILURE(status))
>                         return status;
> -               if (ctrl == *mask)
> -                       break;
> -               decode_osc_control(root, "platform does not support",
> -                                  ctrl & ~(*mask));
> +               if (is_cxl(root)) {
> +                       if (ctrl == *mask && cxl_ctrl == *cxl_mask)
> +                               break;
> +                       pci_missing = ctrl & ~(*mask);
> +                       cxl_missing = cxl_ctrl & ~(*cxl_mask);
> +               } else {
> +                       if (ctrl == *mask)
> +                               break;
> +                       pci_missing = ctrl & ~(*mask);
> +               }
> +               if (pci_missing)
> +                       decode_osc_control(root, "platform does not support",
> +                                          pci_missing);
> +               if (cxl_missing)
> +                       decode_cxl_osc_control(root, "CXL platform does not support",
> +                                          cxl_missing);
>                 ctrl = *mask;
> -       } while (*mask);
> +               cxl_ctrl = *cxl_mask;
> +       } while (*mask || *cxl_mask);
>
>         /* No need to request _OSC if the control was already granted. */
> -       if ((root->osc_control_set & ctrl) == ctrl)
> +       if ((root->osc_control_set & ctrl) == ctrl &&
> +           (root->cxl_osc_control_set & cxl_ctrl) == cxl_ctrl)
>                 return AE_OK;
>
>         if ((ctrl & req) != req) {
> @@ -408,11 +470,17 @@ static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 s
>         capbuf[OSC_QUERY_DWORD] = 0;
>         capbuf[OSC_SUPPORT_DWORD] = root->osc_support_set;
>         capbuf[OSC_CONTROL_DWORD] = ctrl;
> -       status = acpi_pci_run_osc(root, capbuf, mask);
> +       if (is_cxl(root)) {
> +               capbuf[OSC_CXL_SUPPORT_DWORD] = root->cxl_osc_support_set;
> +               capbuf[OSC_CXL_CONTROL_DWORD] = cxl_ctrl;
> +       }
> +
> +       status = acpi_pci_run_osc(root, capbuf, mask, cxl_mask);
>         if (ACPI_FAILURE(status))
>                 return status;
>
>         root->osc_control_set = *mask;
> +       root->cxl_osc_control_set = *cxl_mask;
>         return AE_OK;
>  }
>
> @@ -438,6 +506,19 @@ static u32 calculate_support(void)
>         return support;
>  }
>
> +static u32 calculate_cxl_support(void)
> +{
> +       u32 support;
> +
> +       support = OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT;
> +       if (pci_aer_available())
> +               support |= OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT;
> +       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
> +               support |= OSC_CXL_NATIVE_HP_SUPPORT;
> +
> +       return support;
> +}
> +
>  static u32 calculate_control(void)
>  {
>         u32 control;
> @@ -469,6 +550,16 @@ static u32 calculate_control(void)
>         return control;
>  }
>
> +static u32 calculate_cxl_control(void)
> +{
> +       u32 control = 0;
> +
> +       if (IS_ENABLED(CONFIG_MEMORY_FAILURE))
> +               control |= OSC_CXL_ERROR_REPORTING_CONTROL;
> +
> +       return control;
> +}
> +
>  static bool os_control_query_checks(struct acpi_pci_root *root, u32 support)
>  {
>         struct acpi_device *device = root->device;
> @@ -490,6 +581,7 @@ static bool os_control_query_checks(struct acpi_pci_root *root, u32 support)
>  static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
>  {
>         u32 support, control = 0, requested = 0;
> +       u32 cxl_support = 0, cxl_control = 0, cxl_requested = 0;
>         acpi_status status;
>         struct acpi_device *device = root->device;
>         acpi_handle handle = device->handle;
> @@ -513,10 +605,20 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
>         if (os_control_query_checks(root, support))
>                 requested = control = calculate_control();
>
> -       status = acpi_pci_osc_control_set(handle, &control, support);
> +       if (is_cxl(root)) {
> +               cxl_support = calculate_cxl_support();
> +               decode_cxl_osc_support(root, "OS supports", cxl_support);
> +               cxl_requested = cxl_control = calculate_cxl_control();
> +       }
> +
> +       status = acpi_pci_osc_control_set(handle, &control, support,
> +                                         &cxl_control, cxl_support);
>         if (ACPI_SUCCESS(status)) {
>                 if (control)
>                         decode_osc_control(root, "OS now controls", control);
> +               if (cxl_control)
> +                       decode_cxl_osc_control(root, "OS now controls",
> +                                          cxl_control);
>
>                 if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_ASPM) {
>                         /*
> @@ -545,6 +647,11 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
>                         decode_osc_control(root, "OS requested", requested);
>                         decode_osc_control(root, "platform willing to grant", control);
>                 }
> +               if (cxl_control) {
> +                       decode_cxl_osc_control(root, "OS requested", cxl_requested);
> +                       decode_cxl_osc_control(root, "platform willing to grant",
> +                                          cxl_control);
> +               }
>
>                 dev_info(&device->dev, "_OSC: platform retains control of PCIe features (%s)\n",
>                          acpi_format_exception(status));
> --
> 2.35.1
>
Vishal Verma April 5, 2022, 3:55 p.m. UTC | #5
On Tue, 2022-04-05 at 16:00 +0200, Rafael J. Wysocki wrote:
> On Thu, Mar 31, 2022 at 10:20 PM Vishal Verma <vishal.l.verma@intel.com> wrote:
> > 
> > Add full support for negotiating _OSC as defined in the CXL 2.0 spec, as
> > applicable to CXL-enabled platforms. Advertise support for the CXL
> > features we support - 'CXL 2.0 port/device register access', 'Protocol
> > Error Reporting', and 'CXL Native Hot Plug'. Request control for 'CXL
> > Memory Error Reporting'. The requests are dependent on CONFIG_* based
> > prerequisites, and prior PCI enabling, similar to how the standard PCI
> > _OSC bits are determined.
> > 
> > The CXL specification does not define any additional constraints on
> > the hotplug flow beyond PCIe native hotplug, so a kernel that supports
> > native PCIe hotplug, supports CXL hotplug. For error handling protocol
> > and link errors just use PCIe AER. There is nascent support for
> > amending AER events with CXL specific status [1], but there's
> > otherwise no additional OS responsibility for CXL errors beyond PCIe
> > AER. CXL Memory Errors behave the same as typical memory errors so
> > CONFIG_MEMORY_FAILURE is sufficient to indicate support to platform
> > firmware.
> > 
> > [1]: https://lore.kernel.org/linux-cxl/164740402242.3912056.8303625392871313860.stgit@dwillia2-desk3.amr.corp.intel.com/
> > 
> > Cc: Bjorn Helgaas <bhelgaas@google.com>
> > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > Cc: Robert Moore <robert.moore@intel.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > ---
> >  include/linux/acpi.h    |  28 +++++++-
> >  include/acpi/acpi_bus.h |   6 +-
> >  drivers/acpi/pci_root.c | 145 ++++++++++++++++++++++++++++++++++------
> >  3 files changed, 157 insertions(+), 22 deletions(-)
> > 
> > diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> > index fc40da914315..cf360b9642d9 100644
> > --- a/include/linux/acpi.h
> > +++ b/include/linux/acpi.h
> > @@ -554,10 +554,15 @@ acpi_status acpi_run_osc(acpi_handle handle, struct acpi_osc_context *context);
> >  #define OSC_PCI_CAPABILITY_DWORDS              3
> >  #define OSC_CXL_CAPABILITY_DWORDS              5
> > 
> > -/* Indexes into _OSC Capabilities Buffer (DWORDs 2 & 3 are device-specific) */
> > +/*
> > + * Indexes into _OSC Capabilities Buffer
> > + * DWORDs 2 & 3 are device-specific, and 4 & 5 are specific to CXL platforms
> 
> Say "DWORDs 2 through 5 are device-specific" and you don't need to
> mention CXL here.
> 
> > + */
> >  #define OSC_QUERY_DWORD                                0       /* DWORD 1 */
> >  #define OSC_SUPPORT_DWORD                      1       /* DWORD 2 */
> >  #define OSC_CONTROL_DWORD                      2       /* DWORD 3 */
> > +#define OSC_CXL_SUPPORT_DWORD                  3       /* DWORD 4 */
> > +#define OSC_CXL_CONTROL_DWORD                  4       /* DWORD 5 */
> 
> I would rename the last two symbols as OSC_EXT_SUPPORT_DWORD and
> OSC_EXT_CONTROL_DWORD (see below for an explanation).
> 
> 
Yep, dropping CXL references here and the 'extended' naming sounds
good, I'll update with these changes.
Vishal Verma April 5, 2022, 3:57 p.m. UTC | #6
On Mon, 2022-04-04 at 13:30 -0700, Davidlohr Bueso wrote:
> On Fri, 01 Apr 2022, Dan Williams wrote:
> 
> > On Fri, Apr 1, 2022 at 1:40 PM Davidlohr Bueso <dave@stgolabs.net> wrote:
> > > 
> > > On Thu, 31 Mar 2022, Vishal Verma wrote:
> > > 
> > > > The CXL specification does not define any additional constraints on
> > > > the hotplug flow beyond PCIe native hotplug, so a kernel that supports
> > > > native PCIe hotplug, supports CXL hotplug.
> > > 
> > > Hmm but from a Linux-pov does it make sense to allow hotplug
> > > support if the MM cannot handle it?
> > 
> > I would say yes, i.e. do not consider CONFIG_MEMORY_HOTPLUG for
> > OSC_CXL_NATIVE_HP_SUPPORT, but see below and poke holes in my
> > argument...
> > 
> > > 
> > > @@ -531,7 +518,8 @@ static u32 calculate_cxl_support(void)
> > >         support = OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT;
> > >         if (pci_aer_available())
> > >                 support |= OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT;
> > > -       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
> > > +       if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE) &&
> > > +           IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
> > >                 support |= OSC_CXL_NATIVE_HP_SUPPORT;
> > > 
> > >         return support;
> > > 
> > > After all, per the CXL 2.0 Type 3 device Hot-Add flow:
> > > 
> > > ""
> > > 7. CXL aware software notifies OS memory manager about the new memory and its
> > > attributes such as latency and bandwidth. Memory manager processes a request
> > > and adds the new memory to its allocation pool.
> > > ""
> > 
> > If I look at ACPI hotplug it is true that CONFIG_ACPI_HOTPLUG_MEMORY
> > depends on CONFIG_MEMORY_HOTPLUG. However, it is also true that there
> > is no existing _OSC for memory hotplug support. The reason is that
> > ACPI memory hotplug requires the OS to acknowledge / coordinate with
> > memory plug events via a scan handler. On the CXL side the equivalent
> > would be if Linux supported the Mechanical Retention Lock [1], or
> > otherwise had some coordination for the driver of a PCI device
> > undergoing hotplug to be consulted on whether the hotplug should
> > proceed or not.
> > 
> > The concern is that if Linux says no to supporting CXL hotplug then
> > the BIOS may say no to giving the OS hotplug control of any other PCIe
> > device. So the question here is not whether hotplug is enabled, it's
> > whether it is handled natively by the at all OS, and if
> > CONFIG_HOTPLUG_PCI_PCIE is enabled then the answer is "yes".
> > 
> > Otherwise, the plan for CXL coordinated remove, since the kernel does
> > not support blocking hotplug, is to require the memory device to be
> > disabled before hotplug is attempted. When CONFIG_MEMORY_HOTPLUG is
> > disabled that step will fail and the remove attempt cancelled. by the
> > user. If that is not honored and the card is removed anyway then it
> > does not matter if CONFIG_MEMORY_HOTPLUG is enabled or not, it will
> > cause a crash and other badness.
> > 
> > Long story short, just say yes, to CXL hotplug and require removal to
> > be coordinated by userspace unless and until the kernel grows better
> > mechanisms for doing "managed" removal of devices in consultation with
> > the driver.
> 
> +Cc Adam.
> 
> Thank you for the overview of the landscape; I was assuming this last
> part already existed. I would only suggest documenting the above in
> calculate_cxl_support(), such that future readers don't also wonder
> about this and why CXL doesn't follow what CONFIG_ACPI_HOTPLUG_MEMORY
> does.

I'll document calculate_cxl_support() with this. Thanks Dan and David.

> 
> Thanks,
> Davidlohr
> 
> > 
> > [1]: https://lore.kernel.org/all/20201122014203.4706-1-ashok.raj@intel.com/
diff mbox series

Patch

diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index fc40da914315..cf360b9642d9 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -554,10 +554,15 @@  acpi_status acpi_run_osc(acpi_handle handle, struct acpi_osc_context *context);
 #define OSC_PCI_CAPABILITY_DWORDS		3
 #define OSC_CXL_CAPABILITY_DWORDS		5
 
-/* Indexes into _OSC Capabilities Buffer (DWORDs 2 & 3 are device-specific) */
+/*
+ * Indexes into _OSC Capabilities Buffer
+ * DWORDs 2 & 3 are device-specific, and 4 & 5 are specific to CXL platforms
+ */
 #define OSC_QUERY_DWORD				0	/* DWORD 1 */
 #define OSC_SUPPORT_DWORD			1	/* DWORD 2 */
 #define OSC_CONTROL_DWORD			2	/* DWORD 3 */
+#define OSC_CXL_SUPPORT_DWORD			3	/* DWORD 4 */
+#define OSC_CXL_CONTROL_DWORD			4	/* DWORD 5 */
 
 /* _OSC Capabilities DWORD 1: Query/Control and Error Returns (generic) */
 #define OSC_QUERY_ENABLE			0x00000001  /* input */
@@ -611,6 +616,15 @@  extern u32 osc_sb_native_usb4_control;
 #define OSC_PCI_EXPRESS_LTR_CONTROL		0x00000020
 #define OSC_PCI_EXPRESS_DPC_CONTROL		0x00000080
 
+/* CXL _OSC: Capabilities DWORD 4: Support Field */
+#define OSC_CXL_1_1_PORT_REG_ACCESS_SUPPORT	0x00000001
+#define OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT	0x00000002
+#define OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT	0x00000004
+#define OSC_CXL_NATIVE_HP_SUPPORT		0x00000008
+
+/* CXL _OSC: Capabilities DWORD 5: Control Field */
+#define OSC_CXL_ERROR_REPORTING_CONTROL		0x00000001
+
 static inline u32 acpi_osc_ctx_get_pci_control(struct acpi_osc_context *context)
 {
 	u32 *ret = context->ret.pointer;
@@ -618,6 +632,13 @@  static inline u32 acpi_osc_ctx_get_pci_control(struct acpi_osc_context *context)
 	return ret[OSC_CONTROL_DWORD];
 }
 
+static inline u32 acpi_osc_ctx_get_cxl_control(struct acpi_osc_context *context)
+{
+	u32 *ret = context->ret.pointer;
+
+	return ret[OSC_CXL_CONTROL_DWORD];
+}
+
 #define ACPI_GSB_ACCESS_ATTRIB_QUICK		0x00000002
 #define ACPI_GSB_ACCESS_ATTRIB_SEND_RCV         0x00000004
 #define ACPI_GSB_ACCESS_ATTRIB_BYTE		0x00000006
@@ -1020,6 +1041,11 @@  static inline u32 acpi_osc_ctx_get_pci_control(struct acpi_osc_context *context)
 	return 0;
 }
 
+static inline u32 acpi_osc_ctx_get_cxl_control(struct acpi_osc_context *context)
+{
+	return 0;
+}
+
 #endif	/* !CONFIG_ACPI */
 
 #ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
index 9413d2389711..0fdd913c1fd7 100644
--- a/include/acpi/acpi_bus.h
+++ b/include/acpi/acpi_bus.h
@@ -593,8 +593,10 @@  struct acpi_pci_root {
 	int bridge_type;
 	struct resource secondary;	/* downstream bus range */
 
-	u32 osc_support_set;	/* _OSC state of support bits */
-	u32 osc_control_set;	/* _OSC state of control bits */
+	u32 osc_support_set;		/* _OSC state of support bits */
+	u32 osc_control_set;		/* _OSC state of control bits */
+	u32 cxl_osc_support_set;	/* _OSC state of CXL support bits */
+	u32 cxl_osc_control_set;	/* _OSC state of CXL control bits */
 	phys_addr_t mcfg_addr;
 };
 
diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 5d33bc61fe44..a2e74db28e30 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -142,6 +142,17 @@  static struct pci_osc_bit_struct pci_osc_control_bit[] = {
 	{ OSC_PCI_EXPRESS_DPC_CONTROL, "DPC" },
 };
 
+static struct pci_osc_bit_struct cxl_osc_support_bit[] = {
+	{ OSC_CXL_1_1_PORT_REG_ACCESS_SUPPORT, "CXL11PortRegAccess" },
+	{ OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT, "CXL20PortDevRegAccess" },
+	{ OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT, "CXLProtocolErrorReporting" },
+	{ OSC_CXL_NATIVE_HP_SUPPORT, "CXLNativeHotPlug" },
+};
+
+static struct pci_osc_bit_struct cxl_osc_control_bit[] = {
+	{ OSC_CXL_ERROR_REPORTING_CONTROL, "CXLMemErrorReporting" },
+};
+
 static void decode_osc_bits(struct acpi_pci_root *root, char *msg, u32 word,
 			    struct pci_osc_bit_struct *table, int size)
 {
@@ -170,6 +181,18 @@  static void decode_osc_control(struct acpi_pci_root *root, char *msg, u32 word)
 			ARRAY_SIZE(pci_osc_control_bit));
 }
 
+static void decode_cxl_osc_support(struct acpi_pci_root *root, char *msg, u32 word)
+{
+	decode_osc_bits(root, msg, word, cxl_osc_support_bit,
+			ARRAY_SIZE(cxl_osc_support_bit));
+}
+
+static void decode_cxl_osc_control(struct acpi_pci_root *root, char *msg, u32 word)
+{
+	decode_osc_bits(root, msg, word, cxl_osc_control_bit,
+			ARRAY_SIZE(cxl_osc_control_bit));
+}
+
 static inline bool is_pcie(struct acpi_pci_root *root)
 {
 	return root->bridge_type == ACPI_BRIDGE_TYPE_PCIE;
@@ -198,7 +221,8 @@  static int cap_length(struct acpi_pci_root *root)
 }
 
 static acpi_status acpi_pci_run_osc(struct acpi_pci_root *root,
-				    const u32 *capbuf, u32 *retval)
+				    const u32 *capbuf, u32 *pci_control,
+				    u32 *cxl_control)
 {
 	struct acpi_osc_context context = {
 		.uuid_str = to_uuid(root),
@@ -210,18 +234,20 @@  static acpi_status acpi_pci_run_osc(struct acpi_pci_root *root,
 
 	status = acpi_run_osc(root->device->handle, &context);
 	if (ACPI_SUCCESS(status)) {
-		*retval = acpi_osc_ctx_get_pci_control(&context);
+		*pci_control = acpi_osc_ctx_get_pci_control(&context);
+		if (is_cxl(root))
+			*cxl_control = acpi_osc_ctx_get_cxl_control(&context);
 		kfree(context.ret.pointer);
 	}
 	return status;
 }
 
-static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root,
-					u32 support,
-					u32 *control)
+static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root, u32 support,
+				      u32 *control, u32 cxl_support,
+				      u32 *cxl_control)
 {
 	acpi_status status;
-	u32 result, capbuf[OSC_CXL_CAPABILITY_DWORDS];
+	u32 pci_result, cxl_result, capbuf[OSC_CXL_CAPABILITY_DWORDS];
 
 	support |= root->osc_support_set;
 
@@ -229,11 +255,21 @@  static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root,
 	capbuf[OSC_SUPPORT_DWORD] = support;
 	capbuf[OSC_CONTROL_DWORD] = *control | root->osc_control_set;
 
+	if (is_cxl(root)) {
+		cxl_support |= root->cxl_osc_support_set;
+		capbuf[OSC_CXL_SUPPORT_DWORD] = cxl_support;
+		capbuf[OSC_CXL_CONTROL_DWORD] = *cxl_control | root->cxl_osc_control_set;
+	}
+
 retry:
-	status = acpi_pci_run_osc(root, capbuf, &result);
+	status = acpi_pci_run_osc(root, capbuf, &pci_result, &cxl_result);
 	if (ACPI_SUCCESS(status)) {
 		root->osc_support_set = support;
-		*control = result;
+		*control = pci_result;
+		if (is_cxl(root)) {
+			root->cxl_osc_support_set = cxl_support;
+			*cxl_control = cxl_result;
+		}
 	} else if (is_cxl(root)) {
 		/*
 		 * CXL _OSC is optional on CXL 1.1 hosts. Fall back to PCIe _OSC
@@ -356,6 +392,8 @@  EXPORT_SYMBOL_GPL(acpi_get_pci_dev);
  * @handle: ACPI handle of a PCI root bridge (or PCIe Root Complex).
  * @mask: Mask of _OSC bits to request control of, place to store control mask.
  * @support: _OSC supported capability.
+ * @cxl_mask: Mask of CXL _OSC control bits, place to store control mask.
+ * @cxl_support: CXL _OSC supported capability.
  *
  * Run _OSC query for @mask and if that is successful, compare the returned
  * mask of control bits with @req.  If all of the @req bits are set in the
@@ -366,12 +404,14 @@  EXPORT_SYMBOL_GPL(acpi_get_pci_dev);
  * _OSC bits the BIOS has granted control of, but its contents are meaningless
  * on failure.
  **/
-static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 support)
+static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask,
+					    u32 support, u32 *cxl_mask,
+					    u32 cxl_support)
 {
 	u32 req = OSC_PCI_EXPRESS_CAPABILITY_CONTROL;
 	struct acpi_pci_root *root;
 	acpi_status status;
-	u32 ctrl, capbuf[OSC_CXL_CAPABILITY_DWORDS];
+	u32 ctrl, cxl_ctrl = 0, capbuf[OSC_CXL_CAPABILITY_DWORDS];
 
 	if (!mask)
 		return AE_BAD_PARAMETER;
@@ -383,20 +423,42 @@  static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 s
 	ctrl   = *mask;
 	*mask |= root->osc_control_set;
 
+	if (is_cxl(root)) {
+		cxl_ctrl = *cxl_mask;
+		*cxl_mask |= root->cxl_osc_control_set;
+	}
+
 	/* Need to check the available controls bits before requesting them. */
 	do {
-		status = acpi_pci_query_osc(root, support, mask);
+		u32 pci_missing = 0, cxl_missing = 0;
+
+		status = acpi_pci_query_osc(root, support, mask, cxl_support,
+					    cxl_mask);
 		if (ACPI_FAILURE(status))
 			return status;
-		if (ctrl == *mask)
-			break;
-		decode_osc_control(root, "platform does not support",
-				   ctrl & ~(*mask));
+		if (is_cxl(root)) {
+			if (ctrl == *mask && cxl_ctrl == *cxl_mask)
+				break;
+			pci_missing = ctrl & ~(*mask);
+			cxl_missing = cxl_ctrl & ~(*cxl_mask);
+		} else {
+			if (ctrl == *mask)
+				break;
+			pci_missing = ctrl & ~(*mask);
+		}
+		if (pci_missing)
+			decode_osc_control(root, "platform does not support",
+					   pci_missing);
+		if (cxl_missing)
+			decode_cxl_osc_control(root, "CXL platform does not support",
+					   cxl_missing);
 		ctrl = *mask;
-	} while (*mask);
+		cxl_ctrl = *cxl_mask;
+	} while (*mask || *cxl_mask);
 
 	/* No need to request _OSC if the control was already granted. */
-	if ((root->osc_control_set & ctrl) == ctrl)
+	if ((root->osc_control_set & ctrl) == ctrl &&
+	    (root->cxl_osc_control_set & cxl_ctrl) == cxl_ctrl)
 		return AE_OK;
 
 	if ((ctrl & req) != req) {
@@ -408,11 +470,17 @@  static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 s
 	capbuf[OSC_QUERY_DWORD] = 0;
 	capbuf[OSC_SUPPORT_DWORD] = root->osc_support_set;
 	capbuf[OSC_CONTROL_DWORD] = ctrl;
-	status = acpi_pci_run_osc(root, capbuf, mask);
+	if (is_cxl(root)) {
+		capbuf[OSC_CXL_SUPPORT_DWORD] = root->cxl_osc_support_set;
+		capbuf[OSC_CXL_CONTROL_DWORD] = cxl_ctrl;
+	}
+
+	status = acpi_pci_run_osc(root, capbuf, mask, cxl_mask);
 	if (ACPI_FAILURE(status))
 		return status;
 
 	root->osc_control_set = *mask;
+	root->cxl_osc_control_set = *cxl_mask;
 	return AE_OK;
 }
 
@@ -438,6 +506,19 @@  static u32 calculate_support(void)
 	return support;
 }
 
+static u32 calculate_cxl_support(void)
+{
+	u32 support;
+
+	support = OSC_CXL_2_0_PORT_DEV_REG_ACCESS_SUPPORT;
+	if (pci_aer_available())
+		support |= OSC_CXL_PROTOCOL_ERR_REPORTING_SUPPORT;
+	if (IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
+		support |= OSC_CXL_NATIVE_HP_SUPPORT;
+
+	return support;
+}
+
 static u32 calculate_control(void)
 {
 	u32 control;
@@ -469,6 +550,16 @@  static u32 calculate_control(void)
 	return control;
 }
 
+static u32 calculate_cxl_control(void)
+{
+	u32 control = 0;
+
+	if (IS_ENABLED(CONFIG_MEMORY_FAILURE))
+		control |= OSC_CXL_ERROR_REPORTING_CONTROL;
+
+	return control;
+}
+
 static bool os_control_query_checks(struct acpi_pci_root *root, u32 support)
 {
 	struct acpi_device *device = root->device;
@@ -490,6 +581,7 @@  static bool os_control_query_checks(struct acpi_pci_root *root, u32 support)
 static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
 {
 	u32 support, control = 0, requested = 0;
+	u32 cxl_support = 0, cxl_control = 0, cxl_requested = 0;
 	acpi_status status;
 	struct acpi_device *device = root->device;
 	acpi_handle handle = device->handle;
@@ -513,10 +605,20 @@  static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
 	if (os_control_query_checks(root, support))
 		requested = control = calculate_control();
 
-	status = acpi_pci_osc_control_set(handle, &control, support);
+	if (is_cxl(root)) {
+		cxl_support = calculate_cxl_support();
+		decode_cxl_osc_support(root, "OS supports", cxl_support);
+		cxl_requested = cxl_control = calculate_cxl_control();
+	}
+
+	status = acpi_pci_osc_control_set(handle, &control, support,
+					  &cxl_control, cxl_support);
 	if (ACPI_SUCCESS(status)) {
 		if (control)
 			decode_osc_control(root, "OS now controls", control);
+		if (cxl_control)
+			decode_cxl_osc_control(root, "OS now controls",
+					   cxl_control);
 
 		if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_ASPM) {
 			/*
@@ -545,6 +647,11 @@  static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
 			decode_osc_control(root, "OS requested", requested);
 			decode_osc_control(root, "platform willing to grant", control);
 		}
+		if (cxl_control) {
+			decode_cxl_osc_control(root, "OS requested", cxl_requested);
+			decode_cxl_osc_control(root, "platform willing to grant",
+					   cxl_control);
+		}
 
 		dev_info(&device->dev, "_OSC: platform retains control of PCIe features (%s)\n",
 			 acpi_format_exception(status));