Re: H264 stateless reference frames ordering lists

[Boris Brezillon <boris.brezillon@collabora.com>]

Hi Alexandre,

On Tue, 12 Nov 2019 19:14:22 +0900
Alexandre Courbot <acourbot@google.com> wrote:

> Hi Boris and Ezequiel,
> 
> Patch c3adb85745ca6 has removed the ref_pic_list_* members from the
> v4l2_ctrl_h264_decode_params struct. The MT8183 stateless decoder
> driver I am working on still relies on these lists and I am trying (a
> bit late to the game) to remove them from the Chromium OS kernel UAPI
> in order to match upstream.
> 
> I have dug into the discussion that resulted in this removal and could
> not really find how these are supposed to be reconstructed and on the
> basis on which information. The commit log for the above-mentioned
> patch mentions that "generic helpers will be provided for drivers that
> need this list". I could not find any in the kernel so far, do you
> have any code available at the moment? Or any idea on how these can be
> reconstructed? The process seems to involve reading the DPB itself as
> well as reordering information from the slice parameters, and seems to
> be a bit involved to be done in the kernel, but maybe I am missing
> something here.

The code is here [1], and it should indeed be extracted and put in a
generic v4l2_h264 lib at some point (should happen soon, since we need
the same logic for the rkvdec driver).

Let me know if you have any questions.

Regards,

Boris

[1]https://elixir.bootlin.com/linux/v5.4-rc7/source/drivers/staging/media/hantro/hantro_h264.c#L270