linux-kernel - Re: [PATCH v2] arm64: dts: allwinner: h6: Use dummy regulator for Tanix TX6

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Date:   Tue, 28 Apr 2020 16:21:28 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Clément Péron <peron.clem@...il.com>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Piotr Oniszczuk <warpme@...pl>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] arm64: dts: allwinner: h6: Use dummy regulator for
 Tanix TX6

On 2020-04-28 3:26 pm, Clément Péron wrote:
> Tanix TX6 has a fixed regulator. As DVFS is instructed to change
> voltage to meet OPP table, the DVFS is not working as expected.

Hmm, isn't that really a bug in the DVFS code? I guess it's just blindly 
propagating -EINVAL from the fixed regulators not implementing 
set_voltage, but AFAICS it has no real excuse not to be cleverer and 
still allow switching frequency as long as the voltage *is* high enough 
for the given OPP. I wonder how well it works if the regulator is 
programmable but shared with other consumers... that case probably can't 
be hacked around in DT.

Robin.

> Avoid to introduce a new dedicated OPP Table where voltage are
> equals to the fixed regulator as it will only duplicate all the OPPs.
> Instead remove the fixed regulator so the DVFS framework will create
> dummy regulator and will have the same behavior.
> 
> Add some comments to explain this in the device-tree.
> 
> Reported-by: Piotr Oniszczuk <warpme@...pl>
> Fixes: add1e27fb703 ("arm64: dts: allwinner: h6: Enable CPU opp tables for Tanix TX6")
> Signed-off-by: Clément Péron <peron.clem@...il.com>
> ---
>   .../boot/dts/allwinner/sun50i-h6-tanix-tx6.dts | 18 ++++++++++++++++--
>   1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-h6-tanix-tx6.dts b/arch/arm64/boot/dts/allwinner/sun50i-h6-tanix-tx6.dts
> index be81330db14f..3e96fcb317ea 100644
> --- a/arch/arm64/boot/dts/allwinner/sun50i-h6-tanix-tx6.dts
> +++ b/arch/arm64/boot/dts/allwinner/sun50i-h6-tanix-tx6.dts
> @@ -48,7 +48,15 @@
>   };
>   
>   &cpu0 {
> -	cpu-supply = <&reg_vdd_cpu_gpu>;
> +	/*
> +	 * Don't specify the CPU regulator, as it's a fixed
> +	 * regulator DVFS will not work as it is intructed
> +	 * to reach a voltage which can't be reached.
> +	 * Not specifying a regulator will create a dummy
> +	 * regulator allowing all OPPs.
> +	 *
> +	 * cpu-supply = <&reg_vdd_cpu_gpu>;
> +	 */
>   };
>   
>   &de {
> @@ -68,7 +76,13 @@
>   };
>   
>   &gpu {
> -	mali-supply = <&reg_vdd_cpu_gpu>;
> +	/*
> +	 * Don't specify the GPU regulator, see comment
> +	 * above for the CPU supply.
> +	 *
> +	 * mali-supply = <&reg_vdd_cpu_gpu>;
> +	 */
> +
>   	status = "okay";
>   };
>   
>