linux-kernel - Re: [PATCH v4 12/19] arm64: dts: mediatek: mt8192-asurada: Couple VGPU and VSRAM

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Date:   Thu, 2 Mar 2023 18:03:08 +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 v4 12/19] arm64: dts: mediatek: mt8192-asurada: Couple
 VGPU and VSRAM_OTHER regulators

On Wed, Mar 1, 2023 at 5:55 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" so that we stay in a safe range of
> 0.75-0.80V.
>
> 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 8570b78c04a4..f858eca219d7 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 = <800000>;
> +       regulator-coupled-with = <&mt6315_7_vbuck1>;
> +       regulator-coupled-max-spread = <10000>;

Looking again at the downstream OPP table, it seems there's no voltage
difference requirement. It only needs V_SRAM >= V_GPU. Same applies to
MT8195. Looks like only MT8183 and MT8186 need V_SRAM - V_GPU >= 10000.

Would setting max-spread to 0 work? I ask because with both regulator's
maximum voltage set to 0.8V, there's no way we can reach the highest
OPP.

ChenYu


> +};
> +
>  &mt6359_vufs_ldo_reg {
>         regulator-always-on;
>  };
> @@ -1411,6 +1418,8 @@ mt6315_7_vbuck1: vbuck1 {
>                                 regulator-max-microvolt = <800000>;
>                                 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
>