On Mon, Nov 08, 2021 at 11:42:42PM +0100, Marek Vasut wrote:
> NOTE: This is an RFC patch showing how this mechanism might be workable.
>
> Some platforms require clock to be always running, e.g. because those clock
> 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-clock property of a clock controller
> allows listing clock which must never be turned off.
>
> The implementation here is similar to "protected-clock", except protected
> clock property is currently driver specific. This patch attempts to make
> a generic implementation of "critical-clock" instead.
>
> Unlike "assigned-clocks", the "critical-clock" must be parsed much earlier
> in __clk_register() to assign CLK_IS_CRITICAL flag to clk_init_data .flags
> field. The parsing code obviously need to be cleaned up and factor out into
> separate function.
>
> The new match_clkspec() callback is used to determine whether struct clk_hw
> that is currently being registered matches the clock specifier in the DT
> "critical-clock" property, and if so, then the CLK_IS_CRITICAL is added to
> these newly registered clock. This callback is currently driver specific,
> although I suspect a common and/or generic version of the callback could
> be added. Also, this new callback could possibly be used to replace (*get)
> argument of of_clk_add_hw_provider() later on too.
>
> Thoughts (on the overall design, not code quality or patch splitting) ?
>
> Signed-off-by: Marek Vasut <marex@xxxxxxx>
> Cc: Matti Vaittinen <matti.vaittinen@xxxxxxxxxxxxxxxxx>
> Cc: Michael Turquette <mturquette@xxxxxxxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
> Cc: devicetree@xxxxxxxxxxxxxxx
> Cc: linux-power@xxxxxxxxxxxxxxxxx
> To: linux-clk@xxxxxxxxxxxxxxx
> ---
> .../bindings/clock/clock-bindings.txt | 16 ++++++++++++
> drivers/clk/clk-bd718x7.c | 15 +++++++++++
> drivers/clk/clk.c | 25 +++++++++++++++++++
> include/linux/clk-provider.h | 2 ++
> 4 files changed, 58 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> index f2ea53832ac63..d9a783c35c5a1 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
> +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-clock 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>;
This will need a schema definition in dtschema.
Otherwise, the concept is fine for me.
Rob
