linux-kernel - Re: [PATCH v2 0/4] Make MT8196 get its Mali GPU shader

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Message-ID: <CAPaKu7QST65NPQ7rZAGhqLsb4FN21D-rOvUf-UzgsBCrOv1skA@mail.gmail.com>
Date: Sat, 20 Dec 2025 16:33:26 -0800
From: Chia-I Wu <olvaffe@...il.com>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Cc: Boris Brezillon <boris.brezillon@...labora.com>, Steven Price <steven.price@....com>, 
	Liviu Dudau <liviu.dudau@....com>, 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>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	Ulf Hansson <ulf.hansson@...aro.org>, Chen-Yu Tsai <wenst@...omium.org>, 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, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 0/4] Make MT8196 get its Mali GPU shader_present from nvmem

On Sat, Dec 20, 2025 at 10:50 AM Nicolas Frattaroli
<nicolas.frattaroli@...labora.com> wrote:
>
> The MediaTek MT8196 SoC's Mali SHADER_PRESENT register does not list
> only functional shader cores, but also those that are fused off to
> improve yield.
>
> The SHADER_PRESENT bitmask with the one fused off core omitted is to be
> found in an efuse. However, the efuse address is considered
> confidential, and is not public knowledge.
>
> The MT8196 GPUEB MCU, which does the power management for the Mali GPU
> on this SoC, knows and reads the efuse however, and exposes it in the
> shared memory intended to communicate state to the application
> processor. Reading the bitmask from this shared memory area is the
> vendor's intended solution.
>
> This series models this in the binding and implements it in the
> corresponding Linux drivers:
> - the mali-valhall-csf binding gets an nvmem-cells/nvmem-cell-names
>   property to declare that shader-present is in a different castle
> - the mt8196-gpufreq binding requires nodes to expose the shader-present
>   cell
> - panthor checks for the presence of the shader-present cell and uses it
>   as the shader-present value if it's found, instead of the Mali GPU
>   register contents
> - mtk-mfg-pmdomain becomes an nvmem provider and will happily serve
>   queries for the shader-present cell
>
> While it would be preferable if we could read the efuse directly, it's
> not possible as things stand, and insisting on it will just keep this
> hardware from working in mainline. Running a GPU workload with a
> SHADER_PRESENT bitmask that includes a faulty core results in corrupt
> GPU rendering output.
>
> Modelling the mt8196-gpufreq device as a nvmem-cell provider however is
> not lying about the hardware's capabilities, as it truly does provide
> access to the nvmem-cell, even if it acts as a proxy.
>
> From a bindings and panthor perspective, this is also generic enough to
> where hypothetical other vendors doing the same thing (even with direct
> efuse access) can rely on the same cell name and implementation.
>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Series is Reviewed-by: Chia-I Wu <olvaffe@...il.com>
> ---
> Changes in v2:
> - panthor: move to nvmem_cell_read_variable_le_u64
> - mtk-mfg-pmdomain: put of_node in error path
> - mtk-mfg-pmdomain: remove leftover stray of_node_put on NULL
> - Link to v1: https://lore.kernel.org/r/20251217-mt8196-shader-present-v1-0-f6f8f3aa1e93@collabora.com
>
> ---
> Nicolas Frattaroli (4):
>       dt-bindings: gpu: mali-valhall-csf: Add shader-present nvmem cell
>       dt-bindings: power: mt8196-gpufreq: Describe nvmem provider ability
>       drm/panthor: Implement reading shader_present from nvmem
>       pmdomain: mediatek: mtk-mfg: Expose shader_present as nvmem cell
>
>  .../bindings/gpu/arm,mali-valhall-csf.yaml         | 14 +++++
>  .../bindings/power/mediatek,mt8196-gpufreq.yaml    | 13 +++++
>  drivers/gpu/drm/panthor/panthor_hw.c               | 36 ++++++++++---
>  drivers/pmdomain/mediatek/mtk-mfg-pmdomain.c       | 59 ++++++++++++++++++++++
>  4 files changed, 116 insertions(+), 6 deletions(-)
> ---
> base-commit: 638148c6ffa31d2e4958d51708ff3675221e2da7
> change-id: 20251217-mt8196-shader-present-e2dc3f97fc74
>
> Best regards,
> --
> Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
>