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 10:30:25 +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 v3 11/18] arm64: dts: mediatek: mt8192-asurada: Couple
 VGPU and VSRAM_OTHER regulators

Il 01/03/23 05:53, Chen-Yu Tsai ha scritto:
> 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?
> 

The point was that we'd never get vbuck1 at more than vsram+10mV because
of the constraints that are set with regulator-coupled-max-spread, but
thinking about it again, relying on that is *highly* suboptimal.

Yes, you're right, let's change the constraints on vbuck1 to 800mV: that's
going to be for v4.

Thanks!
Angelo

> 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
>>