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: <5e0e2fbb22c2ffb0c5281727cd95d70f5f5ba696.camel@ndufresne.ca>
Date: Thu, 06 Feb 2025 16:21:10 -0500
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: Krzysztof Kozlowski <krzk@...nel.org>, Florent Tomasin	
 <florent.tomasin@....com>, 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

Le mercredi 05 février 2025 à 10:13 +0100, Krzysztof Kozlowski a écrit :
> On 03/02/2025 16:31, Florent Tomasin wrote:
> > 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.
> 
> Which is a reserved memory, isn't it?
> 
> > 
> > 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.
> 
> 
> I don't talk here really about the driver but even above mediatek
> patchset uses reserved memory bindings.
> 
> You explained some things about driver yet you did not answer the
> question. This looks like reserved memory. If it does not, bring
> arguments why this binding cannot be a reserved memory, why hardware is
> not a carve out memory.

I think the point is that from the Mali GPU view, the memory does not need to be
within the range the Linux Kernel actually see, even though current integration
have that. From Mali GPU driver stand point (or codec drivers and what's not),
the memory range is not useful to allocate protected/restricted memory. On top
of which, its not reserved specifically for the Mali GPU.

What's your practical suggestion here ? Introduce dma_heap_find_by_region() ?

Nicolas

> 
> Best regards,
> Krzysztof
>