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

[Krzysztof Kozlowski <krzk@kernel.org>]

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.

Best regards,
Krzysztof