linux-kernel - Re: [PATCH] ARM: sti: stih410-clocks: Add PROC

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Date:   Mon, 24 Oct 2016 09:53:04 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Peter Griffin <peter.griffin@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...inux.com, patrice.chotard@...com,
        devicetree@...r.kernel.org
Subject: Re: [PATCH] ARM: sti: stih410-clocks: Add PROC_STFE as a critical
 clock

On Tue, 18 Oct 2016, Peter Griffin wrote:

> Once the ST frontend demux HW IP has been enabled, the clock can't
> be disabled otherwise the system will hang and the board will
> be unserviceable.
> 
> To allow balanced clock enable/disable calls in the driver we use
> the critical clock infrastructure to take an extra reference on the
> clock so the clock will never actually be disabled.

This is an abuse of the critical-clocks framework, and is exactly the
type of hack I promised the clk guys I'd try to prevent.  If this, or
any other IP has some quirks (i.e. once enabled, if this clock is
subsequently disabled it will have a catastrophic effect on the
platform), then they should be worked around in the driver.

The correct thing to do here is craft a clk-keep-on flag and ensure it
is set to true for the effected platform(s)' platform data.

> Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> ---
>  arch/arm/boot/dts/stih410-clock.dtsi | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/boot/dts/stih410-clock.dtsi b/arch/arm/boot/dts/stih410-clock.dtsi
> index 8598eff..07c8ef9 100644
> --- a/arch/arm/boot/dts/stih410-clock.dtsi
> +++ b/arch/arm/boot/dts/stih410-clock.dtsi
> @@ -208,7 +208,8 @@
>  						     "clk-clust-hades",
>  						     "clk-hwpe-hades",
>  						     "clk-fc-hades";
> -				clock-critical = <CLK_ICN_CPU>,
> +				clock-critical = <CLK_PROC_STFE>,
> +						 <CLK_ICN_CPU>,
>  						 <CLK_TX_ICN_DMU>,
>  						 <CLK_EXT2F_A9>,
>  						 <CLK_ICN_LMI>,

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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