Re: [PATCH v2 15/23] media: rkvdec: h264: Validate and use pic width and height in mbs

[Nicolas Dufresne <nicolas.dufresne@collabora.com>]

Le samedi 02 avril 2022 à 08:32 -0300, Ezequiel Garcia a écrit :
> Hi Nicolas,
> 
> On Thu, Mar 31, 2022 at 03:37:17PM -0400, Nicolas Dufresne wrote:
> > From: Jonas Karlman <jonas@kwiboo.se>
> > 
> > The width and height in macroblocks is currently configured based on OUTPUT
> > buffer resolution, this works for frame pictures but can cause issues for
> > field pictures.
> > 
> > When frame_mbs_only_flag is 0 the height in mbs should be height of
> > the field instead of height of frame.
> > 
> > Validate pic_width_in_mbs_minus1 and pic_height_in_map_units_minus1
> > against OUTPUT buffer resolution and use these values to configure HW.
> > 
> > Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
> > Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
> > Reviewed-by: Sebastian Fricke <sebastian.fricke@collabora.com>
> > ---
> >  drivers/staging/media/rkvdec/rkvdec-h264.c |  4 ++--
> >  drivers/staging/media/rkvdec/rkvdec.c      | 10 ++++++++++
> >  2 files changed, 12 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/staging/media/rkvdec/rkvdec-h264.c b/drivers/staging/media/rkvdec/rkvdec-h264.c
> > index 8d44a884a52e..a42cf19bcc6d 100644
> > --- a/drivers/staging/media/rkvdec/rkvdec-h264.c
> > +++ b/drivers/staging/media/rkvdec/rkvdec-h264.c
> > @@ -672,8 +672,8 @@ static void assemble_hw_pps(struct rkvdec_ctx *ctx,
> >  		  LOG2_MAX_PIC_ORDER_CNT_LSB_MINUS4);
> >  	WRITE_PPS(!!(sps->flags & V4L2_H264_SPS_FLAG_DELTA_PIC_ORDER_ALWAYS_ZERO),
> >  		  DELTA_PIC_ORDER_ALWAYS_ZERO_FLAG);
> > -	WRITE_PPS(DIV_ROUND_UP(ctx->coded_fmt.fmt.pix_mp.width, 16), PIC_WIDTH_IN_MBS);
> > -	WRITE_PPS(DIV_ROUND_UP(ctx->coded_fmt.fmt.pix_mp.height, 16), PIC_HEIGHT_IN_MBS);
> 
> Please add a comment so we don't forget why we use the bitstream
> fields here.

And perhaps I should clarify that only the height will vary. It remains nice if
we can decode smaller images into larger image/format, that will be needed to
handle the sub-layers in SVC (these are not to be displayed, so we don't care
much about the output stride and all). So that is also an improvement.

> 
> > +	WRITE_PPS(sps->pic_width_in_mbs_minus1 + 1, PIC_WIDTH_IN_MBS);
> > +	WRITE_PPS(sps->pic_height_in_map_units_minus1 + 1, PIC_HEIGHT_IN_MBS);
> >  	WRITE_PPS(!!(sps->flags & V4L2_H264_SPS_FLAG_FRAME_MBS_ONLY),
> >  		  FRAME_MBS_ONLY_FLAG);
> >  	WRITE_PPS(!!(sps->flags & V4L2_H264_SPS_FLAG_MB_ADAPTIVE_FRAME_FIELD),
> > diff --git a/drivers/staging/media/rkvdec/rkvdec.c b/drivers/staging/media/rkvdec/rkvdec.c
> > index 2df8cf4883e2..1b805710e195 100644
> > --- a/drivers/staging/media/rkvdec/rkvdec.c
> > +++ b/drivers/staging/media/rkvdec/rkvdec.c
> > @@ -29,8 +29,11 @@
> >  
> >  static int rkvdec_try_ctrl(struct v4l2_ctrl *ctrl)
> >  {
> > +	struct rkvdec_ctx *ctx = container_of(ctrl->handler, struct rkvdec_ctx, ctrl_hdl);
> > +
> >  	if (ctrl->id == V4L2_CID_STATELESS_H264_SPS) {
> >  		const struct v4l2_ctrl_h264_sps *sps = ctrl->p_new.p_h264_sps;
> > +		unsigned int width, height;
> >  		/*
> >  		 * TODO: The hardware supports 10-bit and 4:2:2 profiles,
> >  		 * but it's currently broken in the driver.
> > @@ -45,6 +48,13 @@ static int rkvdec_try_ctrl(struct v4l2_ctrl *ctrl)
> >  		if (sps->bit_depth_luma_minus8 != 0)
> >  			/* Only 8-bit is supported */
> >  			return -EINVAL;
> > +
> > +		width = (sps->pic_width_in_mbs_minus1 + 1) * 16;
> > +		height = (sps->pic_height_in_map_units_minus1 + 1) * 16;
> > +
> 
> Let's please add a comment here, clarifying it's legal to check
> the coded format (OUTPUT queue format) at .try_ctrl time,
> because the stateless decoder specification [1] mandates
> S_FMT on the OUTPUT queue, before passing the SPS/PPS controls.

Indeed, though I come to see some flaw in the validation. First, the height
formula shall be base on formula 7-18 from the spec:

  FrameHeightInMbs = ( 2 − frame_mbs_only_flag ) * PicHeightInMapUnits

So would be

+		height = (sps->pic_height_in_map_units_minus1 + 1) * 16;
+		if (sps->flags & V4L2_H264_SPS_FLAG_FRAME_MBS_ONLY)
+			height *= 2;

As this driver do interleaved interlaced buffer, not alternate. Finally, we
should validate this again at STREAMON, since userland may have simply omitted
to set the SPS at all. I'll try to improve this and drop the review tag to
ensure this get fully reviewed again.

> 
> [1] https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/dev-stateless-decoder.html
> 
> > +		if (width > ctx->coded_fmt.fmt.pix_mp.width ||
> > +		    height > ctx->coded_fmt.fmt.pix_mp.height)
> 
> Can you add a debug message or error message?
> These silent errors tend to get super hard to track.
> 
> With these changes:
> 
> Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
> 
> Thanks,
> Ezequiel