linux-kernel - Re: [PATCH 03/10] media: uapi: h264: Split prediction weight parameters

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Message-ID: <74dbf137d8838967c6e1433463b2af708be4da03.camel@collabora.com>
Date:   Thu, 30 Jul 2020 09:48:01 -0400
From:   Nicolas Dufresne <nicolas.dufresne@...labora.com>
To:     Alexandre Courbot <acourbot@...omium.org>,
        Ezequiel Garcia <ezequiel@...labora.com>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Tomasz Figa <tfiga@...omium.org>, kernel@...labora.com,
        Jonas Karlman <jonas@...boo.se>,
        Hans Verkuil <hverkuil@...all.nl>,
        Jeffrey Kardatzke <jkardatzke@...omium.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Maxime Ripard <mripard@...nel.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: Re: [PATCH 03/10] media: uapi: h264: Split prediction weight
 parameters

Le samedi 25 juillet 2020 à 22:30 +0900, Alexandre Courbot a écrit :
> On Thu, Jul 16, 2020 at 5:23 AM Ezequiel Garcia <ezequiel@...labora.com> wrote:
> > The prediction weight parameters are only required under
> > certain conditions, which depend on slice header parameters.
> > 
> > The slice header syntax specifies that the prediction
> > weight table is present if:
> > 
> > ((weighted_pred_flag && (slice_type == P || slice_type == SP)) || \
> > (weighted_bipred_idc == 1 && slice_type == B))
> 
> This is a pretty important bit - how about mentioning in the documentation when
> this new control is expected to be present, so both drivers and
> userspace submit it
> or omit it in a consistent manner?

This is copy paste from the spec. We can add a reference to the syntax
chapter in the spec that express exactly this if condition (syntax is
express in pseudo code). The bitstream works exactly the same. Note
that it's not a fault to provide the control even if not needed,
drivers will kindly ignore it.

Reference: 7.3.3 Slice header syntax

Nicolas

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