linux-kernel - Re: [PATCH 00/33] Qualcomm video decoder/encoder driver

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Date:   Mon, 14 Aug 2023 15:58:03 +0300
From:   Stanimir Varbanov <stanimir.k.varbanov@...il.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Vikash Garodia <quic_vgarodia@...cinc.com>, agross@...nel.org,
        andersson@...nel.org, konrad.dybcio@...aro.org, mchehab@...nel.org,
        hans.verkuil@...co.com, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org
Cc:     quic_dikshita@...cinc.com
Subject: Re: [PATCH 00/33] Qualcomm video decoder/encoder driver

Hi Dmitry,

On 28.07.23 г. 17:01 ч., Dmitry Baryshkov wrote:
> On 28/07/2023 16:23, Vikash Garodia wrote:
>> This patch series introduces support for Qualcomm new video acceleration
>> hardware architecture, used for video stream decoding/encoding. This 
>> driver
>> is based on new communication protocol between video hardware and 
>> application
>> processor.
>>
>> This driver comes with below capabilities:
>> - V4L2 complaint video driver with M2M and STREAMING capability.
>> - Supports H264, H265, VP9 decoders.
>> - Supports H264, H265 encoders.
> 
> Please describe, why is it impossible to support this hardware in the 
> venus driver. We do not usually add new drivers for the new generations 
> of the hardware, unless it is fully incompatible with the previous 
> generations. Let me point you to camss or drm/msm drivers. They have 
> successfully solved the issue of supporting multiple generations of the 
> hardware in the same driver.
> 
> Unless the "iris3" is completely different from all the previous 
> generations, I strongly suggest spending time on restructuring existing 
> venus driver and then adding support for the new hardware there instead 
> of dumping out something completely new.

AFAIK the major differences are HW IP and firmware interface (by 
firmware interface I mean a protocol, API and API behavior). The 
firmware and its interface has been re-written to align closely with the 
current v4l2 specs for encoders/decoders state machines [1][2]. On the 
other side current mainline Venus driver firmware is following interface 
similar to OpenMAX.

There are incompatibilities between both firmware interfaces which 
cannot easily combined in a common driver. Even if there is a 
possibility to do that it will lead us to a unreadable driver source 
code and maintenance burden.

Vikash, could elaborate more on firmware interface differences.

[1] 
https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/dev-decoder.html

[2] 
https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/dev-encoder.html

-- 
regards,
Stan