Re: [PATCH 5/5] arm64: dts: mediatek: mt8390-genio-700-evk: Enable Mali GPU

AngeloGioacchino Del Regno
2024-09-23T12:25:11Z

Il 23/09/24 12:14, Pablo Sun ha scritto:
> Hi Angelo,
>
> On 9/23/24 16:45, AngeloGioacchino Del Regno wrote:
> [snipped]
>>
>> Is there any real difference between MT8390 and MT8188 in terms of the GPU OPPs?
>>
>> I see that on MT8188, frequencies up to 880MHz want a DVDD_SRAM_GPU of 0.750V,
>> then 0.775/0.762/0.750 (bin1-4/5/6) on 915MHz, and 0.800/0.775/0.750 (bin1-4/5/6)
>> on 950MHz.
>>
>> Those never call for 0.850V...! So is MT8188 (Chromebooks) wrong, or is MT8390
>> different in that?
>
> To the best of my knowledge, MT8390 and MT8188 has identical GPU
> subsystem. Thus, the OPP table should have no difference.
>
> To be specific, I list the link to the OPP table of Genio 700 EVK
> (MT8390) in reference in [1]. It should match the setting in Chromebook
> kernel branches.
>
> The "typical" voltage in the datasheet is the voltage that would work
> for all frequency settings. As long as it is smaller than the maximum
> operating voltage, setting voltages higher than the ones specified in
> the OPP table does not damage the hardware.
>
> But this 0.85V setting is indeed not optimal. We should follow the
> voltages described in the OPP table, if we want power savings.
>
> I also considered model the regulator setting with 'regulator-coupled-with' and
> 'regulator-coupled-max-spread', but I am not entirely sure how to describe the
> relation that "DVDD_GPU_SRAM should follow DVDD_GPU
> if and only if DVDD_GPU is higher than 0.75V" - should I simply
> set min-voltage to 0.75V and set 'regulator-coupled-with' ?
>

VSRAM_GPU regulator:

regulator-min-microvolt = <750000>;
regulator-max-microvolt = <800000>;
regulator-coupled-with = <&(vgpu regulator)>;
regulator-coupled-max-spread = <1000>;

VGPU regulator:
regulator-min-microvolt = <400000>;
regulator-max-microvolt = <800000>;
regulator-coupled-with = <&(vsram_gpu regulator)>;
regulator-coupled-max-spread = <1000>;

Cheers,
Angelo

> [1]:
> https://gitlab.com/mediatek/aiot/rity/meta-mediatek-bsp/-/blob/kirkstone/recipes-kernel/dtbo/mt8390/gpu-mali.dts
>
> Many thanks,
> Pablo
>