linux-kernel - Re: [PATCH 4/4] clk: dt: st: Introduce clock domain documentation

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Date:	Tue, 27 Jan 2015 17:19:02 -0800
From:	Mike Turquette <mturquette@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:	lee.jones@...aro.org, kernel@...inux.com, sboyd@...eaurora.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 4/4] clk: dt: st: Introduce clock domain documentation

Quoting Lee Jones (2015-01-26 03:14:00)
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  .../devicetree/bindings/clock/st/st,clk-domain.txt | 34 ++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/clock/st/st,clk-domain.txt
> 
> diff --git a/Documentation/devicetree/bindings/clock/st/st,clk-domain.txt b/Documentation/devicetree/bindings/clock/st/st,clk-domain.txt
> new file mode 100644
> index 0000000..7309937
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/st/st,clk-domain.txt
> @@ -0,0 +1,34 @@
> +STMicroelectronics Clock Domain
> +
> +ST hardware have a bunch of clocks which must not 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, the common clk
> +framework will attempt to turn them off and the hardware will
> +subsequently die.  The only way to recover from this failure is to
> +restart.
> +
> +To avoid either of these two scenarios from catastrophically
> +disabling the running system we have implemented a clock domain
> +where clocks are consumed and references are taken, thus preventing
> +them from being shut down by the framework.
> +
> +We use the generic clock bindings found in:
> +  Documentation/devicetree/bindings/clock/clock-bindings.txt
> +
> +Required properties:
> +- compatible : Must be "st,clk-domain"

Seems like a useful feature for any clock provider, not just ST's. Have
you thought about making this solution generic for DT-based clock
providers?

We could amend the common clock binding to include a special "always on"
clock group that is automagically prepared and enabled when the clock
provider/driver is registered, using a common function.

Regards,
Mike

> +
> +Example:
> +
> +clk-domain {
> +       compatible = "st,clk-domain";
> +       clocks = <&clk_s_c0_flexgen CLK_EXT2F_A9>,
> +                <&clk_s_c0_flexgen CLK_COMPO_DVP>,
> +                <&clk_s_c0_flexgen CLK_MMC_1>,
> +                <&clk_s_c0_flexgen CLK_ICN_SBC>,
> +                <&clk_s_c0_flexgen CLK_ICN_LMI>,
> +                <&clk_s_c0_flexgen CLK_ICN_CPU>,
> +                <&clk_s_c0_flexgen CLK_TX_ICN_DMU>,
> +                <&clk_s_a0_flexgen CLK_IC_LMI0>,
> +                <&clk_m_a9>;
> +};
> -- 
> 1.9.1
> 
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