Re: [PATCH v2 for 5.4 3/4] media: hantro: Fix motion vectors usage condition

[Tomasz Figa <tfiga@chromium.org>]

On Tue, Oct 8, 2019 at 10:57 PM Jonas Karlman <jonas@kwiboo.se> wrote:
>
> On 2019-10-08 12:26, Tomasz Figa wrote:
> > On Tue, Oct 8, 2019 at 3:23 PM Jonas Karlman <jonas@kwiboo.se> wrote:
> >> On 2019-10-08 05:29, Tomasz Figa wrote:
> >>> Hi Jonas,
> >>>
> >>> On Tue, Oct 8, 2019 at 3:33 AM Jonas Karlman <jonas@kwiboo.se> wrote:
> >>>> On 2019-10-07 19:45, Ezequiel Garcia wrote:
> >>>>> From: Francois Buergisser <fbuergisser@chromium.org>
> >>>>>
> >>>>> The setting of the motion vectors usage and the setting of motion
> >>>>> vectors address are currently done under different conditions.
> >>>>>
> >>>>> When decoding pre-recorded videos, this results of leaving the motion
> >>>>> vectors address unset, resulting in faulty memory accesses. Fix it
> >>>>> by using the same condition everywhere, which matches the profiles
> >>>>> that support motion vectors.
> >>>> This does not fully match hantro sdk:
> >>>>
> >>>>   enable direct MV writing and POC tables for high/main streams.
> >>>>   enable it also for any "baseline" stream which have main/high tools enabled.
> >>>>
> >>>>   (sps->profile_idc > 66 && sps->constrained_set0_flag == 0) ||
> >>>>   sps->frame_mbs_only_flag != 1 ||
> >>>>   sps->chroma_format_idc != 1 ||
> >>>>   sps->scaling_matrix_present_flag != 0 ||
> >>>>   pps->entropy_coding_mode_flag != 0 ||
> >>>>   pps->weighted_pred_flag != 0 ||
> >>>>   pps->weighted_bi_pred_idc != 0 ||
> >>>>   pps->transform8x8_flag != 0 ||
> >>>>   pps->scaling_matrix_present_flag != 0
> >>> Thanks for double checking this. I can confirm that it's what Hantro
> >>> SDK does indeed.
> >>>
> >>> However, would a stream with sps->profile_idc <= 66 and those other
> >>> conditions met be still a compliant stream?
> >> You are correct, if a non-compliant video is having decoding problems it should probably be handled
> >> on userspace side (by not reporting baseline profile) and not in kernel.
> >> All my video samples that was having the issue fixed in this patch are now decoded correctly.
> >>
> >>>> Above check is used when DIR_MV_BASE should be written.
> >>>> And WRITE_MVS_E is set to nal_ref_idc != 0 when above is true.
> >>>>
> >>>> I think it may be safer to always set DIR_MV_BASE and keep the existing nal_ref_idc check for WRITE_MVS_E.
> >>> That might have a performance penalty or some other side effects,
> >>> though. Otherwise Hantro SDK wouldn't have enable it conditionally.
> >>>
> >>>> (That is what I did in my "media: hantro: H264 fixes and improvements" series, v2 is incoming)
> >>>> Or have you found any video that is having issues in such case?
> >>> We've been running the code with sps->profile_idc > 66 in production
> >>> for 4 years and haven't seen any reports of a stream that wasn't
> >>> decoded correctly.
> >>>
> >>> If we decide to go with a different behavior, I'd suggest thoroughly
> >>> verifying the behavior on a big number of streams, including some
> >>> performance measurements.
> >> I agree, I would however suggest to change the if statement to the following (or similar)
> >> as that should be the optimal for performance reasons and match the hantro sdk.
> >>
> >> if (sps->profile_idc > 66 && dec_param->nal_ref_idc)
> > Sorry for my ignorance, but could you elaborate on this? What's the
> > meaning of nal_ref_idc? I don't see it being checked in the Hantro SDK
> > condition you mentioned earlier.
>
> My somewhat limited understanding of h264 spec is that nal_ref_idc should be 0 for non-reference field/frame/pictures
> and because of this there should not be any need to write motion vector data as the field/frame should not be referenced.
>
> My base for the hantro sdk code is the imx8 imx-vpu-hantro package and it uses (simplified):
>   SetDecRegister(h264_regs, HWIF_WRITE_MVS_E, nal_ref_idc != 0)
> for MVC there is an additional condition.

Aha, completely makes sense. Thanks for clarifying.

Best regards,
Tomasz

>
> Regards,
> Jonas
>
> >
> >> Regards,
> >> Jonas
> >>
> >>> Best regards,
> >>> Tomasz
> >>>
> >>>> Regards,
> >>>> Jonas
> >>>>
> >>>>> Fixes: dea0a82f3d22 ("media: hantro: Add support for H264 decoding on G1")
> >>>>> Signed-off-by: Francois Buergisser <fbuergisser@chromium.org>
> >>>>> Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
> >>>>> ---
> >>>>> v2:
> >>>>> * New patch.
> >>>>>
> >>>>>  drivers/staging/media/hantro/hantro_g1_h264_dec.c | 2 +-
> >>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/staging/media/hantro/hantro_g1_h264_dec.c b/drivers/staging/media/hantro/hantro_g1_h264_dec.c
> >>>>> index 7ab534936843..c92460407613 100644
> >>>>> --- a/drivers/staging/media/hantro/hantro_g1_h264_dec.c
> >>>>> +++ b/drivers/staging/media/hantro/hantro_g1_h264_dec.c
> >>>>> @@ -35,7 +35,7 @@ static void set_params(struct hantro_ctx *ctx)
> >>>>>       if (sps->flags & V4L2_H264_SPS_FLAG_MB_ADAPTIVE_FRAME_FIELD)
> >>>>>               reg |= G1_REG_DEC_CTRL0_SEQ_MBAFF_E;
> >>>>>       reg |= G1_REG_DEC_CTRL0_PICORD_COUNT_E;
> >>>>> -     if (dec_param->nal_ref_idc)
> >>>>> +     if (sps->profile_idc > 66)
> >>>>>               reg |= G1_REG_DEC_CTRL0_WRITE_MVS_E;
> >>>>>
> >>>>>       if (!(sps->flags & V4L2_H264_SPS_FLAG_FRAME_MBS_ONLY) &&
>