Messages in this thread Patch in this message | | | From | Lee Jones <> | Subject | [PATCH v7 5/5] clk: dt: Introduce binding for critical clock support | Date | Wed, 22 Jul 2015 14:04:15 +0100 |
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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
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