Re: [RFCv2 PATCH] em28xx: fix bytesperline calculation in G/TRY_FMT

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em Thu, 31 Jan 2013 08:16:39 +0100
Hans Verkuil <hverkuil@xs4all.nl> escreveu:

> On Wed January 30 2013 20:07:29 Mauro Carvalho Chehab wrote:
> > Em Wed, 30 Jan 2013 10:49:25 +0100
> > Hans Verkuil <hverkuil@xs4all.nl> escreveu:
> > 
> > > On Wed 30 January 2013 10:40:30 Mauro Carvalho Chehab wrote:
> > > > Em Wed, 30 Jan 2013 09:01:22 +0100
> > > > Hans Verkuil <hverkuil@xs4all.nl> escreveu:
> > > > 
> > > > > This was part of my original em28xx patch series. That particular patch
> > > > > combined two things: this fix and the change where TRY_FMT would no
> > > > > longer return -EINVAL for unsupported pixelformats. The latter change was
> > > > > rejected (correctly), but we all forgot about the second part of the patch
> > > > > which fixed a real bug. I'm reposting just that fix.
> > > > > 
> > > > > Changes since v1:
> > > > > 
> > > > > - v1 still miscalculated the bytesperline and imagesize values (they were
> > > > >   too large).
> > > > > - G_FMT had the same calculation bug.
> > > > > 
> > > > > Tested with my em28xx.
> > > > > 
> > > > > Regards,
> > > > > 
> > > > >         Hans
> > > > > 
> > > > > The bytesperline calculation was incorrect: it used the old width instead of
> > > > > the provided width in the case of TRY_FMT, and it miscalculated the bytesperline
> > > > > value for the depth == 12 (planar YUV 4:1:1) case. For planar formats the
> > > > > bytesperline value should be the bytesperline of the widest plane, which is
> > > > > the Y plane which has 8 bits per pixel, not 12.
> > > > > 
> > > > > Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> > > > > ---
> > > > >  drivers/media/usb/em28xx/em28xx-video.c |    8 ++++----
> > > > >  1 file changed, 4 insertions(+), 4 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> > > > > index 2eabf2a..6ced426 100644
> > > > > --- a/drivers/media/usb/em28xx/em28xx-video.c
> > > > > +++ b/drivers/media/usb/em28xx/em28xx-video.c
> > > > > @@ -837,8 +837,8 @@ static int vidioc_g_fmt_vid_cap(struct file *file, void *priv,
> > > > >  	f->fmt.pix.width = dev->width;
> > > > >  	f->fmt.pix.height = dev->height;
> > > > >  	f->fmt.pix.pixelformat = dev->format->fourcc;
> > > > > -	f->fmt.pix.bytesperline = (dev->width * dev->format->depth + 7) >> 3;
> > > > > -	f->fmt.pix.sizeimage = f->fmt.pix.bytesperline  * dev->height;
> > > > > +	f->fmt.pix.bytesperline = dev->width * (dev->format->depth >> 3);
> > > > 
> > > > Why did you remove the round up here?
> > > 
> > > Because that would give the wrong result. Depth can be 8, 12 or 16. The YUV 4:1:1
> > > planar format is the one with depth 12. But for the purposes of the bytesperline
> > > calculation only the depth of the largest plane counts, which is the luma plane
> > > with a depth of 8. So for a width of 720 the value of bytesperline should be:
> > > 
> > > depth=8 -> bytesperline = 720
> > > depth=12 -> bytesperline = 720
> > 
> > With depth=12, it should be, instead, 1080, as 2 pixels need 3 bytes.
> 
> No, it's not. It's a *planar* format: first the Y plane, then the two smaller
> chroma planes. The spec says that bytesperline for planar formats refers to
> the largest plane.
> 
> For this format the luma plane is one byte per pixel. Each of the two chroma
> planes have effectively two bits per pixel (actually one byte per four pixels),
> so you end up with 8+2+2=12 bits per pixel.
> 
> Hence bytesperline should be 720 for this particular format.

If I understood what you just said, you're talking that the only format marked
as depth=12 is actually depth=8, right? Then the fix would be to change depth
in the table, and not here.

Yet, I'm not sure if this is the proper fix.

The only used I saw on userspace apps for this field is to allocate size for
the memory buffer. Some userspace applications use to get bytesperline and
multiply by the image height and get the image size, instead of relying
on sizeimage, as some drivers didn't use to fill sizeimage properly.

By using bytesperline equal to 1080 in this case warrants that the buffers
on userspace will have enough space.

Regards,
Mauro