linux-kernel - Re: [PATCH v3 0/2] media: cedrus: Add H264 decoding support

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Date:   Tue, 12 Feb 2019 18:22:17 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     Tomasz Figa <tfiga@...omium.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Hans Verkuil <hans.verkuil@...co.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Pawel Osciak <posciak@...omium.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg "
         "Roedel <joro@...tes.org>," <linux-arm-kernel@...ts.infradead.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        jenskuske@...il.com, Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>, linux-sunxi@...glegroups.com,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 0/2] media: cedrus: Add H264 decoding support

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@...tlin.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