linux-kernel - Re: [RFC] media: uapi: Move HEVC stateless controls out of staging

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Date:   Mon, 14 Feb 2022 11:01:36 +0100
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Jernej Škrabec <jernej.skrabec@...il.com>,
        mchehab@...nel.org, ezequiel@...guardiasur.com.ar,
        p.zabel@...gutronix.de, gregkh@...uxfoundation.org,
        mripard@...nel.org, paul.kocialkowski@...tlin.com, wens@...e.org,
        jonas@...boo.se, nicolas@...fresne.ca,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        kernel@...labora.com, Alex Bee <knaerzche@...il.com>,
        jc@...esim.co.uk
Subject: Re: [RFC] media: uapi: Move HEVC stateless controls out of staging

Hi all,

On 2/13/22 12:33, Jernej Škrabec wrote:
> Hi Benjamin,
> 
> CC: Alex, John
> 
> Sorry for late response, but I've been very busy last week.
> 
> First of all, thank you for doing this! It's about time that HEVC moves 
> forward.
> 
> Dne torek, 01. februar 2022 ob 13:34:39 CET je Benjamin Gaignard napisal(a):
>> The HEVC stateless 'uAPI' was staging and marked explicitly in the
>> V4L2 specification that it will change and is unstable.
>>
>> Note that these control IDs were never exported as a public API,
>> they were only defined in kernel-local headers (hevc-ctrls.h).
>>
>> While moving the controls out of staging they are renamed and
>> control IDs get new numbers.
>> Drivers (Hantro, Cedrus) and Documentation are updated accordaly.
> 
> accordaly -> accordingly
> 
>>
>> Additional structures fields has been added for RKVDEC driver usage.
> 
> You should do separate patch for that, preceding this one. One patch should 
> only do one thing.
> 
> I also suggest that you add additional patch for removing bit_size field in 
> struct v4l2_ctrl_hevc_slice_params. Similar fields were already removed from 
> MPEG2 and H264 structures. Bit size can be deduced from output buffer size and 
> it doesn't hurt if bit size in Cedrus is set to bigger value than actual slice 
> bit size.
> 
>> Hantro dedicated control is moving to hantro-media.h
>> Since hevc-ctrls.h content has been dispatched in others file, remove it.
>>
>> fluster tests results on IMX8MQ is 77/147 for HEVC codec.
>>
>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> 
> Note that Cedrus still needs additional information in order to decode some 
> HEVC videos. Missing info is num_entry_point_offsets and list of all 
> entry_point_offset_minus1 (obviously, num_entry_point_offsets in size).
> 
> I suggest that this is represented in a new control, which would use dynamic 
> array feature, written by Hans. While Cedrus supports max. 256 entries, it can 
> be much bigger in theory, but in reality, it's much smaller (like 4-8 
> entries).

I've rebased my dynarray tree, so it is up to date again:

https://git.linuxtv.org/hverkuil/media_tree.git/log/?h=dynarray

Regards,

	Hans

> 
> Last but not least, data_bit_offset should be better defined. Currently it 
> points right after last header bit, just like Cedrus needs it. However, there 
> is padding after that, at least 1 bit and 8 bits at most, so slice data always 
> starts from byte aligned address. It probably make sense to rework that field 
> to be byte offset, not bit, just like in VA-API. Note that RPi HEVC driver also 
> uses byte aligned address directly. Cedrus would need some kind of workaround 
> and only one that works is this one:
> https://github.com/bootlin/libva-v4l2-request/blob/master/src/h265.c#L191-L209
> 
> Best regards,
> Jernej
> 
>