Re: [PATCH v2] media: mediatek: vcodec: fix h264 cavlc bitstream fail

[AngeloGioacchino Del Regno]

Il 15/11/22 03:00, Yunfei Dong (董云飞) ha scritto:
> Hi AngeloGioacchino,
>
> Thanks for your detail suggestion.
> On Mon, 2022-11-14 at 12:08 +0100, AngeloGioacchino Del Regno wrote:
> > Il 18/10/22 13:41, Yunfei Dong ha scritto:
> > > Some cavlc bistream will decode fail when the frame size is small
> > > than
> >
> > s/small/smaller/g
>
> Will fix in next patch.
> > > 20 bytes. Need to add pending data at the end of the bitstream.
> > >
> > > For the minimum size of mapped memory is 256 bytes(16x16), adding
> > > four bytes data
> > > won't lead to access unknown virtual memory.
> > >
> > > Fixes: 59fba9eed5a7 ("media: mediatek: vcodec: support stateless
> > > H.264 decoding for mt8192")
> > > Signed-off-by: Yunfei Dong <yunfei.dong@xxxxxxxxxxxx>
> > > ---
> > > compared with v1:
> > > - add detail comments for function: vdec_h264_insert_startcode.
> > > - re-write commit message.
> > > ---
> > >    .../vcodec/vdec/vdec_h264_req_multi_if.c      | 32
> > > +++++++++++++++++--
> > >    1 file changed, 29 insertions(+), 3 deletions(-)
> > >
> > > diff --git
> > > a/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_i
> > > f.c
> > > b/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_i
> > > f.c
> > > index 4cc92700692b..18e048755d11 100644
> > > ---
> > > a/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_i
> > > f.c
> > > +++
> > > b/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_i
> > > f.c
> > > @@ -539,6 +539,29 @@ static int vdec_h264_slice_core_decode(struct
> > > vdec_lat_buf *lat_buf)
> > >    	return 0;
> > >    }
> > >    
> > > +static void vdec_h264_insert_startcode(struct mtk_vcodec_dev
> > > *vcodec_dev, unsigned char *buf,
> > > +				       size_t *bs_size, struct
> > > mtk_h264_pps_param *pps)
> > > +{
> > > +	struct device *dev = &vcodec_dev->plat_dev->dev;
> > > +
> > > +	/* Need to add pending data at the end of bitstream when bs_sz
> > > is small than
> > > +	 * 20 bytes for cavlc bitstream, or lat will decode fail. This
> > > pending data is
> > > +	 * useful for mt8192 and mt8195 platform.
> >
> > What is the reason why other SoCs don't need this?
> For the hardware not add this feature, and will add in the future Soc.
> > > +	 *
> > > +	 * cavlc bitstream when entropy_coding_mode_flag is false.
> > > +	 */
> > > +	if (pps->entropy_coding_mode_flag || *bs_size > 20 ||
> > > +	    !(of_device_is_compatible(dev->of_node, "mediatek,mt8192-
> > > vcodec-dec") ||
> > > +	    of_device_is_compatible(dev->of_node, "mediatek,mt8195-
> > > vcodec-dec")))
> >
> > I'm not comfortable seeing of_device_is_compatible... this list will
> > grow whenever
> > a new SoC needing this appears.
> > Please think about a good name for a flag/quirk, or a bool, in the
> > platform data
> > for these two SoCs and use it.
> For this feature only need to add in these two Socs, and won't grow
> anymore. So just want to use compatible to separate, not add one flags.
>
> So you think that using one flag to separate much better?

A flag is better: please remember that calls to of_device_is_compatible()
will perform a string comparison which, as you know, as much optimized as
it can be, it's always going to be slower than a simple integer/bool/flag
check.

This means that even for functional (not just cosmetic) reasons we should
not use of_device_is_compatible() here :-)

Cheers,
Angelo