linux-kernel - Re: [PATCH v3 11/18] arm64: dts: mediatek: mt8192-asurada: Couple VGPU and VSRAM

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Date:   Wed, 1 Mar 2023 12:53:43 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     matthias.bgg@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3 11/18] arm64: dts: mediatek: mt8192-asurada: Couple
 VGPU and VSRAM_OTHER regulators

On Tue, Feb 28, 2023 at 6:47 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> Add coupling for these regulators, as VSRAM_OTHER is used to power the
> GPU SRAM, and they have a strict voltage output relation to satisfy in
> order to ensure GPU stable operation.
> While at it, also add voltage constraint overrides for the GPU SRAM
> regulator "mt6359_vsram_others", but don't touch mt6315's vbuck1 as
> its constraints are fine.

The minimum voltage on vbuck1 matches the lowest OPP. However the maximum
voltage is set to the maximum of the regulator itself. The MT8192 datasheet
says the absolute maximum for the GPU is 0.8V, and the recommended range
for 0.8V is 0.72V ~ 0.88V. The highest OPP we have is 0.8V, so I would
just set the maximum voltage to that?

ChenYu

> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>  arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
> index df477eb89f21..c8b6e1a9605b 100644
> --- a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
> +++ b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
> @@ -447,6 +447,13 @@ &mt6359_vrf12_ldo_reg {
>         regulator-always-on;
>  };
>
> +&mt6359_vsram_others_ldo_reg {
> +       regulator-min-microvolt = <750000>;
> +       regulator-max-microvolt = <850000>;
> +       regulator-coupled-with = <&mt6315_7_vbuck1>;
> +       regulator-coupled-max-spread = <10000>;
> +};
> +
>  &mt6359_vufs_ldo_reg {
>         regulator-always-on;
>  };
> @@ -1411,6 +1418,8 @@ mt6315_7_vbuck1: vbuck1 {
>                                 regulator-max-microvolt = <1193750>;
>                                 regulator-enable-ramp-delay = <256>;
>                                 regulator-allowed-modes = <0 1 2>;
> +                               regulator-coupled-with = <&mt6359_vsram_others_ldo_reg>;
> +                               regulator-coupled-max-spread = <10000>;
>                         };
>                 };
>         };
> --
> 2.39.2
>