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

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Message-ID: <5dba27e1-d480-ea24-c1ba-03bb7f77b1b1@collabora.com>
Date:   Thu, 2 Mar 2023 11:17:14 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chen-Yu Tsai <wenst@...omium.org>
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

Il 02/03/23 11:03, Chen-Yu Tsai ha scritto:
> 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.

On MT8195 we don't need any regulator coupling. There, the GPU-SRAM voltage
is fixed at .. I don't remember, 0.7V? - anyway - MT8195 doesn't need to
scale the vsram.

> 
> 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.
> 

No that doesn't work. I can raise the Vgpu max voltage to 0.88V to solve the
issue right here and right now, or we can leave it like that and revisit it
later.

I would at this point go for setting mt6315_7_vbuck1's max-microvolt to
880000, as this is the maximum recommended voltage for the GPU as per the
MT8192 datasheet, it would also make sense as we would be still describing
the hardware in a correct manner.

What do you think?

Angelo

> 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
>>

-- 
AngeloGioacchino Del Regno
Software Engineer

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