| Message ID | 1437570255-21049-6-git-send-email-lee.jones@linaro.org |
|---|---|
| State | New |
| Headers | show |
On Mon, 27 Jul 2015, Maxime Ripard wrote: > Hi Lee, > > On Wed, Jul 22, 2015 at 02:04:15PM +0100, Lee Jones wrote: > > Signed-off-by: Lee Jones <lee.jones@linaro.org> > > --- > > .../devicetree/bindings/clock/clock-bindings.txt | 39 ++++++++++++++++++++++ > > 1 file changed, 39 insertions(+) > > > > diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt > > index 06fc6d5..4137034 100644 > > --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt > > +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt > > @@ -44,6 +44,45 @@ For example: > > clocks by index. The names should reflect the clock output signal > > names for the device. > > > > +critical-clock: Some hardware contains bunches of clocks which, in normal > > + circumstances, must never be turned off. If drivers a) fail to > > + obtain a reference to any of these or b) give up a previously > > + obtained reference during suspend, it is possible that some > > + Operating Systems might attempt to disable them to save power. > > + If this happens a platform can fail irrecoverably as a result. > > + Usually the only way to recover from these failures is to > > + reboot. > > + > > + To avoid either of these two scenarios from catastrophically > > + disabling an otherwise perfectly healthy running system, > > + clocks can be identified as 'critical' using this property from > > + inside a clocksource's node. > > + > > + This property is not to be abused. It is only to be used to > > + protect platforms from being crippled by gated clocks, NOT as a > > + convenience function to avoid using the framework correctly > > + inside device drivers. > > + > > + Expected values are hardware clock indices. If the > > + clock-indices property (see below) is used, then supplied > > + values must correspond to one of the listed identifiers. > > + Using the clock-indices example below, hardware clock <2> > > + is missing, therefore it is considered invalid to then > > + list clock <2> as a critical clock. > > I think we should also consider having it simply as a boolean. Using > indices for clocks that don't have any (for example because it only > provides a single clock) seem to not really make much sense. Then how would you distinguish between the clocks if the provider provides more than a single clock? > Also, since you can have a bunch of them, using critical-clocks seem > more appropriate. I can change the name to critical-clocks, no problem.
On Tue, 28 Jul 2015, Maxime Ripard wrote: > On Mon, Jul 27, 2015 at 08:31:49AM +0100, Lee Jones wrote: > > On Mon, 27 Jul 2015, Maxime Ripard wrote: > > > > > Hi Lee, > > > > > > On Wed, Jul 22, 2015 at 02:04:15PM +0100, Lee Jones wrote: > > > > Signed-off-by: Lee Jones <lee.jones@linaro.org> > > > > --- > > > > .../devicetree/bindings/clock/clock-bindings.txt | 39 ++++++++++++++++++++++ > > > > 1 file changed, 39 insertions(+) > > > > > > > > diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt > > > > index 06fc6d5..4137034 100644 > > > > --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt > > > > +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt > > > > @@ -44,6 +44,45 @@ For example: > > > > clocks by index. The names should reflect the clock output signal > > > > names for the device. > > > > > > > > +critical-clock: Some hardware contains bunches of clocks which, in normal > > > > + circumstances, must never be turned off. If drivers a) fail to > > > > + obtain a reference to any of these or b) give up a previously > > > > + obtained reference during suspend, it is possible that some > > > > + Operating Systems might attempt to disable them to save power. > > > > + If this happens a platform can fail irrecoverably as a result. > > > > + Usually the only way to recover from these failures is to > > > > + reboot. > > > > + > > > > + To avoid either of these two scenarios from catastrophically > > > > + disabling an otherwise perfectly healthy running system, > > > > + clocks can be identified as 'critical' using this property from > > > > + inside a clocksource's node. > > > > + > > > > + This property is not to be abused. It is only to be used to > > > > + protect platforms from being crippled by gated clocks, NOT as a > > > > + convenience function to avoid using the framework correctly > > > > + inside device drivers. > > > > + > > > > + Expected values are hardware clock indices. If the > > > > + clock-indices property (see below) is used, then supplied > > > > + values must correspond to one of the listed identifiers. > > > > + Using the clock-indices example below, hardware clock <2> > > > > + is missing, therefore it is considered invalid to then > > > > + list clock <2> as a critical clock. > > > > > > I think we should also consider having it simply as a boolean. Using > > > indices for clocks that don't have any (for example because it only > > > provides a single clock) seem to not really make much sense. > > > > Then how would you distinguish between the clocks if the provider > > provides more than a single clock? > > What I had in mind was that, you would have three cases: > > - critical-clocks is not there: no clocks are made critical > > - critical-clocks is there, but doesn't have any values: all the > clocks provided are marked critical > > - critical-clocks is there and it has a list of values: only the > clocks listed are marked critical. > > Does that make sense to you? Yep, sounds good.
diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt index 06fc6d5..4137034 100644 --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt @@ -44,6 +44,45 @@ For example: clocks by index. The names should reflect the clock output signal names for the device. +critical-clock: Some hardware contains bunches of clocks which, in normal + circumstances, must never be turned off. If drivers a) fail to + obtain a reference to any of these or b) give up a previously + obtained reference during suspend, it is possible that some + Operating Systems might attempt to disable them to save power. + If this happens a platform can fail irrecoverably as a result. + Usually the only way to recover from these failures is to + reboot. + + To avoid either of these two scenarios from catastrophically + disabling an otherwise perfectly healthy running system, + clocks can be identified as 'critical' using this property from + inside a clocksource's node. + + This property is not to be abused. It is only to be used to + protect platforms from being crippled by gated clocks, NOT as a + convenience function to avoid using the framework correctly + inside device drivers. + + Expected values are hardware clock indices. If the + clock-indices property (see below) is used, then supplied + values must correspond to one of the listed identifiers. + Using the clock-indices example below, hardware clock <2> + is missing, therefore it is considered invalid to then + list clock <2> as a critical clock. + +For example: + + oscillator { + #clock-cells = <1>; + clock-output-names = "ckil", "ckih"; + critical-clock = <0>, <1>; + }; + +- this node defines a device with two clock outputs, just as in the + example above. The only difference being that 'ckil' and 'ckih' + are now identified as an critical clocks, so an OS will know to + never attempt to gate them. + clock-indices: If the identifying number for the clocks in the node is not linear from zero, then this allows the mapping of identifiers into the clock-output-names array.
Signed-off-by: Lee Jones <lee.jones@linaro.org> --- .../devicetree/bindings/clock/clock-bindings.txt | 39 ++++++++++++++++++++++ 1 file changed, 39 insertions(+)