linux-kernel - Re: [PATCH v3 3/3] arm64: dts: mediatek: mt8370: Enable gpu support

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Message-ID: <9cbd03f7-c3e4-433b-96ee-3b9683fccdd2@collabora.com>
Date: Tue, 11 Feb 2025 10:28:25 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
 Louis-Alexis Eyraud <louisalexis.eyraud@...labora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Matthias Brugger
 <matthias.bgg@...il.com>, Boris Brezillon <boris.brezillon@...labora.com>,
 Steven Price <steven.price@....com>, kernel@...labora.com,
 dri-devel@...ts.freedesktop.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 3/3] arm64: dts: mediatek: mt8370: Enable gpu support

Il 11/02/25 09:31, Krzysztof Kozlowski ha scritto:
> On Fri, Feb 07, 2025 at 04:18:32PM +0100, Louis-Alexis Eyraud wrote:
>> Add a new gpu node in mt8370.dtsi to enable support for the
>> ARM Mali G57 MC2 GPU (Valhall-JM) found on the MT8370 SoC, using the
>> Panfrost driver.
>>
>> On a Mediatek Genio 510 EVK board, the panfrost driver probed with the
>> following message:
>> ```
>> panfrost 13000000.gpu: clock rate = 390000000
>> panfrost 13000000.gpu: mali-g57 id 0x9093 major 0x0 minor 0x0 status 0x0
>> panfrost 13000000.gpu: features: 00000000,000019f7, issues: 00000003,
>>     80000400
>> panfrost 13000000.gpu: Features: L2:0x08130206 Shader:0x00000000
>>     Tiler:0x00000809 Mem:0x1 MMU:0x00002830 AS:0xff JS:0x7
>> panfrost 13000000.gpu: shader_present=0x5 l2_present=0x1
>> [drm] Initialized panfrost 1.3.0 for 13000000.gpu on minor 0
>> ```
>>
>> Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@...labora.com>
>> ---
>>   arch/arm64/boot/dts/mediatek/mt8370.dtsi | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/mediatek/mt8370.dtsi b/arch/arm64/boot/dts/mediatek/mt8370.dtsi
>> index cf1a3759451ff899ce9e63e5a00f192fb483f6e5..2f27f7e7ab813b97f869297ae360f69854e966e1 100644
>> --- a/arch/arm64/boot/dts/mediatek/mt8370.dtsi
>> +++ b/arch/arm64/boot/dts/mediatek/mt8370.dtsi
>> @@ -59,6 +59,15 @@ &cpu_little3_cooling_map0 {
>>   				<&cpu3 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
>>   };
>>   
>> +&gpu {
>> +	compatible = "mediatek,mt8370-mali", "arm,mali-valhall-jm";
> 
> It's up to platform maintainers, but IMHO this is discouraged practice.
> If you ever need to override compatible, this means the node is not
> really shared between this and base SoC (base DTSI).
> 

That's true, indeed, but this is a special case, where the GPU actually is really
architecturally and generationally the same, difference being that one core is
lasered off from the lower binned silicon.

I appreciate you pointing that out, and effectively we shall not create any
misunderstanding on this practice, which shall remain discouraged.

Speaking of which!

Louis, since you anyway have to send a v4, please add a comment before that
gpu node override saying:

/*
  * Please note that overriding compatibles is a discouraged practice and is a
  * clear indication of nodes not being, well, compatible!
  *
  * This is a special case, where the GPU is the same as MT8188, but with one
  * of the cores fused out in this lower-binned SoC.
  */
&gpu {
  ....etc


Thanks,
Angelo