On Mon, Jul 27, 2015 at 08:31:49AM +0100, Lee Jones wrote:

On Mon, 27 Jul 2015, Maxime Ripard wrote:

quoted

Hi Lee,

On Wed, Jul 22, 2015 at 02:04:15PM +0100, Lee Jones wrote:

quoted

Signed-off-by: Lee Jones <redacted>
---
 .../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?

Thanks,
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com