[v7,5/5] clk: dt: Introduce binding for critical clock support

Message ID 1437570255-21049-6-git-send-email-lee.jones@linaro.org
State New
Headers show

Commit Message

Lee Jones July 22, 2015, 1:04 p.m.
Signed-off-by: Lee Jones <lee.jones@linaro.org>
---
 .../devicetree/bindings/clock/clock-bindings.txt   | 39 ++++++++++++++++++++++
 1 file changed, 39 insertions(+)

Comments

Lee Jones July 27, 2015, 7:31 a.m. | #1
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.
Lee Jones July 30, 2015, 9:23 a.m. | #2
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.

Patch

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.