linux-kernel - Re: [RFC PATCH 3/5] dt-bindings: gpu: Add protected heap name to Mali Valhall CSF binding

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Message-ID: <4b9deab1-e330-4c93-8260-75276c2bc9ff@arm.com>
Date: Mon, 3 Feb 2025 15:31:09 +0000
From: Florent Tomasin <florent.tomasin@....com>
To: Krzysztof Kozlowski <krzk@...nel.org>, Vinod Koul <vkoul@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 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>,
 Sumit Semwal <sumit.semwal@...aro.org>,
 Benjamin Gaignard <benjamin.gaignard@...labora.com>,
 Brian Starkey <Brian.Starkey@....com>, John Stultz <jstultz@...gle.com>,
 "T . J . Mercier" <tjmercier@...gle.com>,
 Christian König <christian.koenig@....com>,
 Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Yong Wu <yong.wu@...iatek.com>
Cc: dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org,
 nd@....com, Akash Goel <akash.goel@....com>
Subject: Re: [RFC PATCH 3/5] dt-bindings: gpu: Add protected heap name to Mali
 Valhall CSF binding

Hi Krzysztof

On 30/01/2025 13:25, Krzysztof Kozlowski wrote:
> On 30/01/2025 14:08, Florent Tomasin wrote:
>> Allow mali-valhall-csf driver to retrieve a protected
>> heap at probe time by passing the name of the heap
>> as attribute to the device tree GPU node.
> 
> Please wrap commit message according to Linux coding style / submission
> process (neither too early nor over the limit):
> https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/process/submitting-patches.rst#L597
Apologies, I think I made quite few other mistakes in the style of the
patches I sent. I will work on improving this aspect, appreciated

> Why this cannot be passed by phandle, just like all reserved regions?
> 
> From where do you take these protected heaps? Firmware? This would
> explain why no relation is here (no probe ordering, no device links,
> nothing connecting separate devices).

The protected heap is generaly obtained from a firmware (TEE) and could
sometimes be a carved-out memory with restricted access.

The Panthor CSF kernel driver does not own or manage the protected heap
and is instead a consumer of it (assuming the heap is made available by
the system integrator).

I initially used a phandle, but then I realised it would introduce a new
API to share the heap across kernel driver. In addition I found this
patch series:
-
https://lore.kernel.org/lkml/20230911023038.30649-1-yong.wu@mediatek.com/#t

which introduces a DMA Heap API to the rest of the kernel to find a
heap by name:
- dma_heap_find()

I then decided to follow that approach to help isolate the heap
management from the GPU driver code. In the Panthor driver, if the
heap is not found at probe time, the driver will defer the probe until
the exporter made it available.

Best regards,
Florent