Re: [PATCH v2 3/3] media: uapi: h264: Get rid of the p0/b0/b1 ref-lists

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

On Wed, 26 Jun 2019 13:33:41 +0200
Paul Kocialkowski <paul.kocialkowski@bootlin.com> wrote:

> Hi,
> 
> On Mon, 2019-06-10 at 10:52 +0200, Boris Brezillon wrote:
> > Those lists can be extracted from the dpb, let's simplify userspace
> > life and build that list kernel-side (generic helpers will be provided
> > for drivers that need this list).  
> 
> I don't really have any clear idea about that, but there was a
> discussion about DPB vs reference picture lists some weeks ago.

What we call DPB right now is actually a list of reference pictures
(each entry being flagged long or short term). When reading the spec,
you said DPB was referring to something that's more implementation
specific, and I think that's what motivated your initial suggestion to
rename this field into something more appropriate (ref_pics?). TBH, I'm
just guessing here, since you were the one initially proposing this
change, and I must say that having to explain what you had in mind at
that time is a bit weird :P.

> 
> Is there some mail thread with a rationale about it, some IRC logs I
> could look at or could the people involved in the discussion provide
> some additional background at this point?

Well, you were part of the discussion, and I think most of it happened
in the "Proposed updates and guidelines for MPEG-2, H.264 and H.265
stateless support" thread you started.

> 
> IIRC we also talked about removing the DPB or at least renaming it, but
> I don't have a clear idea of the outcome as well.

The list of long/short refs has to be passed, and that's actually what
we currently call "DPB", so we're just talking about a rename here,
nothing more. The ordered P/B0/B1 reflists can easily be built from the
un-ordered list of ref pics, so I'm just proposing to get rid of these
fields and have a generic implementation kernel-side so that drivers
that need it don't have to re-implement it.