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

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Message-ID: <bf45531a-eacf-22a9-65f1-f6474a2ca843@mediatek.com>
Date: Mon, 23 Sep 2024 18:14:38 +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>,
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
CC: <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-mediatek@...ts.infradead.org>,
	<linux-clk@...r.kernel.org>
Subject: Re: [PATCH 5/5] arm64: dts: mediatek: mt8390-genio-700-evk: Enable
 Mali GPU

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' ?

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

Many thanks,
Pablo