On Thu, Apr 28, 2022 at 01:01:06PM +0200, Marek Vasut wrote:
> Some platforms require select clock to be always running, e.g. because
> those clock supply vital devices which are not otherwise attached to
> the system and thus do not have a matching DT node and clock consumer.
>
> An example is a system where the SoC serves as a crystal oscillator
> replacement for a programmable logic device. The "critical-clocks"
> property of a clock controller allows listing clock which must never
> be turned off.
>
> Clock listed in the "critical-clocks" property may have other consumers
> in DT, listing the clock in "critical-clocks" only assures those clock
> are never turned off, and none of these optional additional consumers
> can turn the clock off either.
>
> The implementation is modeled after "protected-clocks".
>
> Signed-off-by: Marek Vasut <marex@xxxxxxx>
> Cc: Michael Turquette <mturquette@xxxxxxxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
> Cc: devicetree@xxxxxxxxxxxxxxx
> To: linux-clk@xxxxxxxxxxxxxxx
> ---
> V2: Update the commit message to clarify the behavior
> ---
> .../devicetree/bindings/clock/clock-bindings.txt | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
As mentioned on IRC, I'm okay with the property, but want Stephen's
opinion on it. It also needs to be a schema in dtschema with the rest of
the clock binding. I've submitted a patch to redirect this file to the
schema.
>
> diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> index f2ea53832ac6..975230e603d1 100644
> --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
> +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> @@ -169,6 +169,22 @@ a shared clock is forbidden.
> Configuration of common clocks, which affect multiple consumer devices can
> be similarly specified in the clock provider node.
>
> +==Critical clocks==
> +
> +Some platforms require clock to be always running, e.g. because those clock
require some clocks
> +supply devices which are not otherwise attached to the system. One example
> +is a system where the SoC serves as a crystal oscillator replacement for a
> +programmable logic device. The critical-clocks property of a clock controller
> +allows listing clock which must never be turned off.
> +
> + clock-controller@a000f000 {
> + compatible = "vendor,clk95;
> + reg = <0xa000f000 0x1000>
> + #clocks-cells = <1>;
> + ...
> + critical-clocks = <UART3_CLK>, <SPI5_CLK>;
> + };
> +
> ==Protected clocks==
>
> Some platforms or firmwares may not fully expose all the clocks to the OS, such
> --
> 2.35.1
>
>
