Re: [PATCH v7 09/12] media: rkvdec: Add get_image_fmt ops

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

Le lundi 07 avril 2025 à 13:09 +0200, Hans Verkuil a écrit :
> On 25/02/2025 10:40, Sebastian Fricke wrote:
> > From: Jonas Karlman <jonas@kwiboo.se>
> > 
> > Add support for a get_image_fmt() ops that returns the required image
> > format.
> > 
> > The CAPTURE format is reset when the required image format changes and
> > the buffer queue is not busy.
> > 
> > Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
> > Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
> > Tested-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
> > Tested-by: Christopher Obbard <chris.obbard@collabora.com>
> > ---
> >  drivers/staging/media/rkvdec/rkvdec.c | 49 +++++++++++++++++++++++++++++++++--
> >  drivers/staging/media/rkvdec/rkvdec.h |  2 ++
> >  2 files changed, 49 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/staging/media/rkvdec/rkvdec.c b/drivers/staging/media/rkvdec/rkvdec.c
> > index 70154948b4e32e2c439f259b0f1e1bbc8b52b063..5394079509305c619f1d0c1f542bfc409317c3b7 100644
> > --- a/drivers/staging/media/rkvdec/rkvdec.c
> > +++ b/drivers/staging/media/rkvdec/rkvdec.c
> > @@ -111,15 +111,60 @@ static int rkvdec_try_ctrl(struct v4l2_ctrl *ctrl)
> >  {
> >  	struct rkvdec_ctx *ctx = container_of(ctrl->handler, struct rkvdec_ctx, ctrl_hdl);
> >  	const struct rkvdec_coded_fmt_desc *desc = ctx->coded_fmt_desc;
> > +	struct v4l2_pix_format_mplane *pix_mp = &ctx->decoded_fmt.fmt.pix_mp;
> > +	enum rkvdec_image_fmt image_fmt;
> > +	struct vb2_queue *vq;
> > +	int ret;
> > +
> > +	if (desc->ops->try_ctrl) {
> > +		ret = desc->ops->try_ctrl(ctx, ctrl);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> > +	if (!desc->ops->get_image_fmt)
> > +		return 0;
> >  
> > -	if (desc->ops->try_ctrl)
> > -		return desc->ops->try_ctrl(ctx, ctrl);
> > +	image_fmt = desc->ops->get_image_fmt(ctx, ctrl);
> > +	if (ctx->image_fmt == image_fmt)
> > +		return 0;
> > +
> > +	if (rkvdec_is_valid_fmt(ctx, pix_mp->pixelformat, image_fmt))
> > +		return 0;
> > +
> > +	/* format change not allowed when queue is busy */
> > +	vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx,
> > +			     V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE);
> > +	if (vb2_is_busy(vq))
> > +		return -EINVAL;
> 
> This makes no sense to me. This just tries a control, and that should just
> work, regardless of vb2_is_busy(). It's a 'try', so you are not actually
> changing anything.

See comment below, notice that this code is only reached if the control
introduce parameters that are not compatible with the current capture
queue fmt. The entire function uses "success" early exit, so the
further down you get in the function, the less likely your control is
valid.

> 
> > +
> > +	return 0;
> > +}
> > +
> > +static int rkvdec_s_ctrl(struct v4l2_ctrl *ctrl)
> > +{
> > +	struct rkvdec_ctx *ctx = container_of(ctrl->handler, struct rkvdec_ctx, ctrl_hdl);
> > +	const struct rkvdec_coded_fmt_desc *desc = ctx->coded_fmt_desc;
> > +	struct v4l2_pix_format_mplane *pix_mp = &ctx->decoded_fmt.fmt.pix_mp;
> > +	enum rkvdec_image_fmt image_fmt;
> > +
> > +	if (!desc->ops->get_image_fmt)
> > +		return 0;
> > +
> > +	image_fmt = desc->ops->get_image_fmt(ctx, ctrl);
> > +	if (ctx->image_fmt == image_fmt)
> > +		return 0;
> 
> If you really can't set a control when the queue is busy, then that should
> be tested here, not in try_ctrl. And then you return -EBUSY.
> 
> Am I missing something here?

When I reviewed, I had imagine that s_ctrl on a request would just run
a try. Now that I read that more careful, I see that it does a true set
on separate copy. So yes, this can safely be moved here.

Since you seem wondering "If you really can't set a control", let me
explain what Jonas wants to protect against. RKVdec does not have any
color conversion code, the header compound control (which header
depends on the codec), contains details such as sub-sampling and color
depth. Without color conversion, when the image format is locked (the
busy queue), you can't request the HW to decode a frame witch does not
fit. This could otherwise lead to buffer overflow in the HW,
fortunately protected by the iommu, but you don't really want to depend
on the mmu.

I've never used try_ctrl in my decade of v4l2, so obviously, now that I
know that s_ctrl on request is not a try, I'm fine with rejecting this
PR, sending a new version and making a PR again. But if I was to use
this API in userspace, my intuitive expectation would be that this
should fail try(), even if its very rarely valid to check the queue
state in try control.

Nicolas

> 
> Regards,
> 
> 	Hans
> 
> > +
> > +	ctx->image_fmt = image_fmt;
> > +	if (!rkvdec_is_valid_fmt(ctx, pix_mp->pixelformat, ctx->image_fmt))
> > +		rkvdec_reset_decoded_fmt(ctx);
> >  
> >  	return 0;
> >  }
> >  
> >  static const struct v4l2_ctrl_ops rkvdec_ctrl_ops = {
> >  	.try_ctrl = rkvdec_try_ctrl,
> > +	.s_ctrl = rkvdec_s_ctrl,
> >  };
> >  
> >  static const struct rkvdec_ctrl_desc rkvdec_h264_ctrl_descs[] = {
> > diff --git a/drivers/staging/media/rkvdec/rkvdec.h b/drivers/staging/media/rkvdec/rkvdec.h
> > index 6f8cf50c5d99aad2f52e321f54f3ca17166ddf98..e466a2753ccfc13738e0a672bc578e521af2c3f2 100644
> > --- a/drivers/staging/media/rkvdec/rkvdec.h
> > +++ b/drivers/staging/media/rkvdec/rkvdec.h
> > @@ -73,6 +73,8 @@ struct rkvdec_coded_fmt_ops {
> >  		     struct vb2_v4l2_buffer *dst_buf,
> >  		     enum vb2_buffer_state result);
> >  	int (*try_ctrl)(struct rkvdec_ctx *ctx, struct v4l2_ctrl *ctrl);
> > +	enum rkvdec_image_fmt (*get_image_fmt)(struct rkvdec_ctx *ctx,
> > +					       struct v4l2_ctrl *ctrl);
> >  };
> >  
> >  enum rkvdec_image_fmt {
> > 

-- 
Nicolas Dufresne
Principal Engineer at Collabora