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SubjectRe: [PATCH v3 0/2] media: cedrus: Add H264 decoding support
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Hey Tomasz,

On Tue, 2019-02-12 at 21:50 +0900, Tomasz Figa wrote:
> Hi Maxime,
>
> On Mon, Feb 11, 2019 at 11:39 PM Maxime Ripard
> <maxime.ripard@bootlin.com> wrote:
> > Hi,
> >
> > Here is a new version of the H264 decoding support in the cedrus
> > driver.
>
> Thanks for working on this. Please see my comments below.
>
> > As you might already know, the cedrus driver relies on the Request
> > API, and is a reverse engineered driver for the video decoding engine
> > found on the Allwinner SoCs.
> >
> > This work has been possible thanks to the work done by the people
> > behind libvdpau-sunxi found here:
> > https://github.com/linux-sunxi/libvdpau-sunxi/
> >
> > I've tested the various ABI using this gdb script:
> > http://code.bulix.org/jl4se4-505620?raw
> >
> > And this test script:
> > http://code.bulix.org/8zle4s-505623?raw
> >
> > The application compiled is quite trivial:
> > http://code.bulix.org/e34zp8-505624?raw
> >
> > The output is:
> > arm: builds/arm-test-v4l2-h264-structures
> > SHA1: 88cbf7485ba81831fc3b93772b215599b3b38318
> > x86: builds/x86-test-v4l2-h264-structures
> > SHA1: 88cbf7485ba81831fc3b93772b215599b3b38318
> > x64: builds/x64-test-v4l2-h264-structures
> > SHA1: 88cbf7485ba81831fc3b93772b215599b3b38318
> > arm64: builds/arm64-test-v4l2-h264-structures
> > SHA1: 88cbf7485ba81831fc3b93772b215599b3b38318
> >
> > Let me know if there's any flaw using that test setup, or if you have
> > any comments on the patches.
> >
> > Maxime
> >
> > Changes from v2:
> > - Simplified _cedrus_write_ref_list as suggested by Jernej
> > - Set whether the frame is used as reference using nal_ref_idc
> > - Respect chroma_format_idc
> > - Fixes for the scaling list and prediction tables
> > - Wrote the documentation for the flags
> > - Added a bunch of defines to the driver bit fields
> > - Reworded the controls and data format descriptions as suggested
> > by Hans
> > - Reworked the controls' structure field size to avoid padding
> > - Removed the long term reference flag
>
> This and...
>

Maxime has dropped this because of Ayaka's mail about long term references
not making much sense in stateless decoders.

I noticed that RK3399 TRM has a field to specify long term refs and
so was wondering about this item as well.

> > - Reintroduced the neighbor info buffer
> > - Removed the ref_pic_list_p0/b0/b1 arrays that are redundant with the
> > one in the DPB
>
> these are used in our Rockchip VDEC driver.
>
> Could you elaborate on the reasons why they got removed?
>

If I understood correctly, there are two reference picture lists.
P-frames will populate ref_pic_list0 and B-frames will populate both.

According to this, v4l2_ctrl_h264_slice_param.ref_pic_list0 and .ref_pic_list1
should be enough and ref_pic_list_p0/b0/b1 are not needed.

What do you think?

Regards,
Ezequiel

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