Re: [PATCH v3 1/3] media: rkvdec: Fix .buf_prepare

[Ezequiel Garcia <ezequiel@collabora.com>]

On Tue, 2020-05-05 at 15:56 +0200, Tomasz Figa wrote:
> Hi Ezequiel,
> 
> On Tue, May 5, 2020 at 3:41 PM Ezequiel Garcia <ezequiel@collabora.com> 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.
> 
> Thanks for the patch. Just one question below.
> 
> Where does the requirement to set OUTPUT buffer bytesused to sizeimage
> if the original bytesused is 0 come from?
> 

If I'm reading english correctly, it's here:

https://www.kernel.org/doc/html/latest/media/uapi/v4l/buffer.html

"""
The number of bytes occupied by the data in the buffer. It depends on the negotiated data format and may change with each buffer for compressed
variable size data like JPEG images. Drivers must set this field when type refers to a capture stream, applications when it refers to an output
stream. If the application sets this to 0 for an output stream, then bytesused will be set to the size of the buffer (see the length field of this
struct) by the driver. For multiplanar formats this field is ignored and the planes pointer is used instead.
"""

Thanks!
Ezequiel

> Best regards,
> Tomasz
> 
> > Fix it.
> > 
> > Fixes: cd33c830448ba ("media: rkvdec: Add the rkvdec driver")
> > Signed-off-by: Ezequiel Garcia <ezequiel@collabora.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);
> >         return 0;
> >  }
> > 
> > --
> > 2.26.0.rc2
> >