linux-kernel - Re: [PATCH v4 1/3] media: rkvdec: Fix .buf

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Date:   Wed, 20 May 2020 10:12:40 -0300
From:   Ezequiel Garcia <ezequiel@...labora.com>
To:     Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Tomasz Figa <tfiga@...omium.org>, kernel@...labora.com,
        Jonas Karlman <jonas@...boo.se>,
        Heiko Stuebner <heiko@...ech.de>,
        Alexandre Courbot <acourbot@...omium.org>,
        Jeffrey Kardatzke <jkardatzke@...omium.org>,
        gustavo.padovan@...labora.com,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>
Subject: Re: [PATCH v4 1/3] media: rkvdec: Fix .buf_prepare

On Wed, 2020-05-20 at 15:07 +0200, Hans Verkuil wrote:
> On 18/05/2020 19:40, Ezequiel Garcia wrote:
> > The driver should only set the payload on .buf_prepare
> > if the buffer is CAPTURE type, or if an OUTPUT buffer
> > has a zeroed payload.
> > 
> > Fix it.
> > 
> > Fixes: cd33c830448ba ("media: rkvdec: Add the rkvdec driver")
> > Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
> > ---
> >  drivers/staging/media/rkvdec/rkvdec.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/staging/media/rkvdec/rkvdec.c b/drivers/staging/media/rkvdec/rkvdec.c
> > index 225eeca73356..4df2a248ab96 100644
> > --- a/drivers/staging/media/rkvdec/rkvdec.c
> > +++ b/drivers/staging/media/rkvdec/rkvdec.c
> > @@ -456,7 +456,15 @@ static int rkvdec_buf_prepare(struct vb2_buffer *vb)
> >  		if (vb2_plane_size(vb, i) < sizeimage)
> >  			return -EINVAL;
> >  	}
> > -	vb2_set_plane_payload(vb, 0, f->fmt.pix_mp.plane_fmt[0].sizeimage);
> > +
> > +	/*
> > +	 * Buffer's bytesused is written by the driver for CAPTURE buffers,
> > +	 * or if the application passed zero bytesused on an OUTPUT buffer.
> > +	 */
> > +	if (!V4L2_TYPE_IS_OUTPUT(vq->type) ||
> > +	    (V4L2_TYPE_IS_OUTPUT(vq->type) && !vb2_get_plane_payload(vb, 0)))
> > +		vb2_set_plane_payload(vb, 0,
> > +				      f->fmt.pix_mp.plane_fmt[0].sizeimage);
> 
> This should just be:
> 
> 	if (!V4L2_TYPE_IS_OUTPUT(vq->type))
> 		vb2_set_plane_payload(vb, 0, f->fmt.pix_mp.plane_fmt[0].sizeimage);
> 
> If the application passes 0 as bytesused, then 1) a warning will be generated
> by the v4l2 core and 2) the v4l2 core will set bytesused to the length of the
> buffer. See vb2_fill_vb2_v4l2_buffer() in videobuf2-v4l2.c.
> 
> Some old drivers explicitly allow bytesused to be 0 for an output queue to
> signal end-of-stream, but that's only supported if the allow_zero_bytesused
> flag is set in the vb2_queue, and that shall not be used for new drivers
> since it is deprecated functionality.
> 

Ah, good catch. I'll get you a v5.

Thanks,
Ezequiel