linux-kernel - Re: [RFC PATCH 0/3] Implement Region of Interest(ROI) support.

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Message-ID: <0232a3fc-8774-4540-a718-eddb1d89e6d2@oss.qualcomm.com>
Date: Thu, 15 Jan 2026 16:38:10 -0800
From: Deepa Guthyappa Madivalara <deepa.madivalara@....qualcomm.com>
To: Nicolas Dufresne <nicolas@...fresne.ca>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Vikash Garodia <vikash.garodia@....qualcomm.com>,
        Dikshita Agarwal <dikshita.agarwal@....qualcomm.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Bryan O'Donoghue <bod@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] Implement Region of Interest(ROI) support.


On 1/15/2026 5:42 AM, Nicolas Dufresne wrote:
> Hi,
>
> Le mercredi 14 janvier 2026 à 14:14 -0800, Deepa Guthyappa Madivalara a écrit
>
>
> [...]
>
>> Thanks for the quick comments.
>> Qp map for can be too much data to be sent from user space to firmware
>> via control per frame.
>> Ex: Avc has mbsize as 16 and the max mbpf iris driver supports is 8192x4352.
>> This would mean 136kb of data (8bit Qp) needs to be transferred for each
>> frame in worst case.
>> While are still evaluating Qp map option, due to firmware performance
>> issues we are
>> gravitating more towards rectangle ROI.
>> I am not sure if we will need to support the Qp map in the future.
> Have you read how this is implemented in Vulkan and D3D12 ? Please have a read:
>
> - Vulkan Video, see quantizationMapTexelSize [0]
> - D3D, see QPMapRegionPixelsSize [1]
>
> [0] https://docs.vulkan.org/features/latest/features/proposals/VK_KHR_video_encode_quantization_map.html
> [1] https://microsoft.github.io/DirectX-Specs/d3d/D3D12_Video_Encoding_Texture_QPMap_DirtyMap_MotionVectors.html
>
> Note that D3D also support dirty regions (what you call ROI in this proposal),
> with no limits, since these are translated into map by drivers (its a software
> feature on top) and motion search hints, that one seems rare.
>
> I'm not against having ROI in our API, its common in older chips designs, but
> its clearly going away in the long run since most fixed hardware impose very low
> region count, which is not usable for modern application. ROI it trivial to
> implement on top of QP maps.
>
> A typical use case for that is to use lightweight AI or traditional CV to locate
> most relevant portion of a video. The result is more like a heat map, not a set
> of rectangles. Then we roughly map that in a low granularity QPMap before
> encoding. This allow maintaining very low bandwidth, while preserving the
> information needed for the heavier processing in the cloud. I'm including one of
> the many example of that, this is a talk from Spiideo [2].
>
> [2] https://gstconf.ubicast.tv/videos/region-based-compression-in-gstreamer/
>
>
> regards,
> Nicolas
Thank you for the detailed information. I reviewed the documentation
and agree with your assessment. I am following up with my team to 
explore this further.

Thanks,
Deepa