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

Lee Jones
2015-07-22T13:15:53Z

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.
+
+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.
--
1.9.1