linux-kernel - Re: [PATCH v3 1/5] media: dt-bindings: add non-pixel property in iris schema

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Message-ID: <9f5be122-302d-402f-91f2-675507612d32@oss.qualcomm.com>
Date: Wed, 2 Jul 2025 15:11:25 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Vikash Garodia <quic_vgarodia@...cinc.com>,
        Dikshita Agarwal <quic_dikshita@...cinc.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc: linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] media: dt-bindings: add non-pixel property in iris
 schema

On 7/2/25 1:46 PM, Krzysztof Kozlowski wrote:
> On 02/07/2025 13:32, Vikash Garodia wrote:
>>
>> On 7/2/2025 4:43 PM, Krzysztof Kozlowski wrote:
>>> On 27/06/2025 17:48, Vikash Garodia wrote:
>>>> Existing definition limits the IOVA to an addressable range of 4GiB, and
>>>> even within that range, some of the space is used by IO registers,
>>>> thereby limiting the available IOVA to even lesser. Video hardware is
>>>> designed to emit different stream-ID for pixel and non-pixel buffers,
>>>> thereby introduce a non-pixel sub node to handle non-pixel stream-ID.
>>>>
>>>> With this, both iris and non-pixel device can have IOVA range of 0-4GiB
>>>> individually. Certain video usecases like higher video concurrency needs
>>>> IOVA higher than 4GiB.
>>>>
>>>> Add reference to the reserve-memory schema, which defines reserved IOVA

[...]

>>>>    dma-coherent: true
>>>>  
>>>> +  non-pixel:
>>>
>>> Why EXISTING hardware grows?
>> Same here, the commit describes the limitation of existing design and also
>> explains the need for having the non-pixel device. Its not that the hardware is
>> growing here, rather the hardware stream-IDs are utilized differently to get
>> higher device addressable range.
> 
> You are not doing this for a new device. There is no new device here at
> all. Nowhere here is a new device.
> 
> Changes for a new device COME TOGETHER with the new device.
> 
> What you are doing here is changing existing hardware without any
> explanation why.

This is bindings getting a reality check.. this goes as far back as Venus
existed (msm8974/2012)

We unfortunately have to expect a number of similar updates for all
multimedia peripherals (GPU/Camera/Display etc.), as certain mappings
must be done through certain SIDs (which are deemed 'secure') and some
hardware has general addressing limitations that may have been causing
silent issues all along

Konrad