linux-kernel - Re: [PATCH v2 2/3] media: cedrus: Fix H264 default reference index count

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Date:   Thu, 03 Oct 2019 22:44:31 +0200
From:   Jernej Škrabec <jernej.skrabec@...l.net>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     mripard@...nel.org, mchehab@...nel.org, hverkuil-cisco@...all.nl,
        gregkh@...uxfoundation.org, wens@...e.org,
        linux-media@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] media: cedrus: Fix H264 default reference index count

Dne četrtek, 03. oktober 2019 ob 22:28:46 CEST je Paul Kocialkowski 
napisal(a):
> Hi,
> 
> On Thu 03 Oct 19, 07:16, Jernej Škrabec wrote:
> > Dne četrtek, 03. oktober 2019 ob 00:06:50 CEST je Paul Kocialkowski
> > 
> > napisal(a):
> > > Hi,
> > > 
> > > On Wed 02 Oct 19, 21:35, Jernej Skrabec wrote:
> > > > Reference index count in VE_H264_PPS should come from PPS control.
> > > > However, this is not really important, because reference index count
> > > > is
> > > > in our case always overridden by that from slice header.
> > > 
> > > Thanks for the fixup!
> > > 
> > > Our libva userspace and v4l2-request testing tool currently don't
> > > provide
> > > this, but I have a pending merge request adding it for the hantro so
> > > it's
> > > good to go.
> > 
> > Actually, I think this is just cosmetic and it would work even if it would
> > be always 0. We always override this number in SHS2 register with
> > VE_H264_SHS2_NUM_REF_IDX_ACTIVE_OVRD flag and recently there was a patch
> > merged to clarify that value in slice parameters should be the one that's
> > set on default value if override flag is not set in bitstream:
> > https://git.linuxtv.org/media_tree.git/commit/?
> > id=187ef7c5c78153acdce8c8714e5918b1018c710b
> > 
> > Well, we could always compare default and value in slice parameters, but I
> > really don't see the benefit of doing that extra work.
> 
> Thanks for the detailed explanation! So I just realized that for HEVC, I
> didn't even include the default value in PPS and only went for the
> per-slice value. The HEVC hardware block apparently only needs the fields
> once at slice level, and by looking at the spec, only one of the two set of
> fields will be used.
> 
> So perhaps we could do the same for H.264 and only have the set of fields
> once in the slice params, so that both codecs are consistent. Userspace can
> just check the flag to know whether it should put the PPS default or
> slice-specific value in the slice-specific control.
> 
> What do you think?

I think that there would be less confusion if only value in slice params would 
exists. But since Philipp rather made clarification in documentation, maybe he 
sees benefit having both values?

Best regards,
Jernej

> 
> Cheers,
> 
> Paul
> 
> > Best regards,
> > Jernej
> > 
> > > Acked-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > > 
> > > Cheers,
> > > 
> > > Paul
> > > 
> > > > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > > > ---
> > > > 
> > > >  drivers/staging/media/sunxi/cedrus/cedrus_h264.c | 8 ++------
> > > >  1 file changed, 2 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > > b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c index
> > > > bd848146eada..4a0e69855c7f 100644
> > > > --- a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > > @@ -364,12 +364,8 @@ static void cedrus_set_params(struct cedrus_ctx
> > > > *ctx,
> > > > 
> > > >  	// picture parameters
> > > >  	reg = 0;
> > > > 
> > > > -	/*
> > > > -	 * FIXME: the kernel headers are allowing the default value to
> > > > -	 * be passed, but the libva doesn't give us that.
> > > > -	 */
> > > > -	reg |= (slice->num_ref_idx_l0_active_minus1 & 0x1f) << 10;
> > > > -	reg |= (slice->num_ref_idx_l1_active_minus1 & 0x1f) << 5;
> > > > +	reg |= (pps->num_ref_idx_l0_default_active_minus1 & 0x1f) << 10;
> > > > +	reg |= (pps->num_ref_idx_l1_default_active_minus1 & 0x1f) << 5;
> > > > 
> > > >  	reg |= (pps->weighted_bipred_idc & 0x3) << 2;
> > > >  	if (pps->flags & V4L2_H264_PPS_FLAG_ENTROPY_CODING_MODE)
> > > >  	
> > > >  		reg |= VE_H264_PPS_ENTROPY_CODING_MODE;