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

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Message-ID: <30184391-12a6-c095-7862-35c7677b0ede@mediatek.com>
Date: Thu, 12 Sep 2024 19:38:10 +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,

On 9/12/24 15:52, AngeloGioacchino Del Regno wrote:
[snip]
>>
> 
> The range should match the target device's Vin constraints; in this 
> case, it
> should be no lower than the minimum working voltage of the Vgpu-in of 
> the Mali IP.
> 
> The drivers will be responsible of setting the lowest possible voltage for
> enhanced efficiency (power saving), taking into account the fused chip 
> quality bits
> (in this case, the MediaTek SVS driver!).
> 
> You should, at this point, check the constraints of SVS, as in, given a 
> reference
> voltage (in this case, located in the GPU OPP table, the voltage 
> associated with
> the lowest frequency of the GPU), what is the maximum voltage 
> *subtraction* that
> SVS will do on the VGPU?
> 
> After the subtraction, may this voltage be lower than 0.546V? :-)

Thanks for the clear explanation. While there are no explicit constraint 
in the maximum voltage subtraction in the SVS driver, I have
confirmed that the fuse data of MT8395 is written in a way that the SVS
driver would never go lower than the minimum recommended operating
voltage of DVDD_GPU in the datasheet[1], which supplies power to the 
Mali IP.

I have sent patch v2 to remove the always-on property and add a note
about the fuse(eFuse) data in [2].


[1]: 
https://mediatek-marketing.files.svdcdn.com/production/documents/MTK_MT8395_Application-Processor-Datasheet_v1.8.pdf?dm=1724252510
[2]: https://lkml.org/lkml/2024/9/12/285

Many thanks,
Pablo