linux-kernel - Re: [PATCH] arm64: dts: mediatek: mt8395-genio-1200-evk: Enable GPU

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Message-ID: <2fd45240-a341-806b-f336-78d0595a8031@mediatek.com>
Date: Wed, 11 Sep 2024 18:35:48 +0800
From: Pablo Sun <pablo.sun@...iatek.com>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Rob
 Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor
 Dooley <conor+dt@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>
CC: <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH] arm64: dts: mediatek: mt8395-genio-1200-evk: Enable GPU

Hi Angelo,

Thanks for the review,

On 9/11/24 16:57, AngeloGioacchino Del Regno wrote:

[snip]

>> +/* for GPU SRAM */
>> +&mt6359_vsram_others_ldo_reg {
>> +    regulator-always-on;
> 
> No, that's not good. Like that, the GPU VSRAM will be subject to current 
> leakage.
> 
> Remove the regulator-always-on property.
> The right way of doing that is to add the vgpu to the mfg0's domain 
> supply and
> vsram to mfg1; that way all of the GPU regulators will be off at PM 
> suspend time.

Thanks for pointing this out, I'll send v2 to fix this.

>>   &mt6359codec {
>>       mediatek,mic-type-0 = <1>; /* ACC */
>>       mediatek,mic-type-1 = <3>; /* DCC */
>> @@ -839,8 +851,8 @@ regulators {
>>               mt6315_7_vbuck1: vbuck1 {
>>                   regulator-compatible = "vbuck1";
>>                   regulator-name = "Vgpu";
>> -                regulator-min-microvolt = <300000>;
>> -                regulator-max-microvolt = <1193750>;
>> +                regulator-min-microvolt = <546000>;
> 
> I'm okay with this constraint but are you sure that MTK-SVS won't go any 
> lower than 0.546V?

I'll see if I could confirm the maximum voltage drop that may be lowered 
by mtk-svs for MT8395. There are 3 constraints that I am aware of:

- capability of Vgpu buck: 0.3V-1.193V
- sign-off voltage of the EVK board: 0.6V to 1.2V
- recommended operating voltage of MT8395 DVDD_GPU: 0.546V to 0.787V

For the device tree of the board, would you recommend set the regulator 
voltage constraints in narrower range (because it's safer to keep in 
recommended operating conditions), or in a wider range (leaving the 
check to driver software for potential power saving?)

Thanks