Hi Sylwester,
On Wed, Nov 7, 2012 at 3:52 AM, Sylwester Nawrocki
<sylvester.nawrocki@xxxxxxxxx> wrote:
> Hi All,
>
> I'd like to clarify the meaning of selection targets on a mem-to-mem video
> device, in order to document it and to make sure new m2m drivers get it
> right, and also that the existing ones, using originally the crop ioctls,
> are converted to the selection ioctls properly.
>
> Until the selections API was introduced we used the CROP ioctls to configure
> cropping on OUTPUT buffer queue and composition onto CAPTURE buffer.
> Looking at Figure 1.2, [1] it seems obvious that there should be applied
> following mapping of the CROP to SELECTION ioctls:
>
> S_CROP(V4L2_BUF_TYPE_VIDEO_OUTPUT) ->
> S_SELECTION(V4L2_BUF_TYPE_VIDEO_OUTPUT,
> V4L2_SEL_TGT_CROP)
>
> S_CROP(V4L2_BUF_TYPE_VIDEO_CAPTURE) ->
> S_SELECTION(V4L2_BUF_TYPE_VIDEO_CAPTURE,
> V4L2_SEL_TGT_COMPOSE)
>
> And that's how selections are currently documented at video output and
> capture interfaces:
>
> --------------------------------------------------------------------------------
> *Configuration of video output*
>
> For output devices targets and ioctls are used similarly to the video
> capture
> case. The composing rectangle refers to the insertion of an image into a
> video
> signal. The cropping rectangles refer to a memory buffer."
>
>
> *Configuration of video capture*
> ... The top left corner, width and height of the source rectangle, that is
> the
> area actually sampled, is given by the V4L2_SEL_TGT_CROP target.
> ...
> The composing targets refer to a memory buffer.
> --------------------------------------------------------------------------------
>
> If we apply this mapping, then current VIDIOC_S/G_CROP ->
> VIDIOC_S/G_SELECTION
> ioctl fallback code wouldn't be valid, as we have there, e.g.
>
> static int v4l_s_crop(const struct v4l2_ioctl_ops *ops,
> struct file *file, void *fh, void *arg)
> {
> struct v4l2_crop *p = arg;
> struct v4l2_selection s = {
> .type = p->type,
> .r = p->c,
> };
>
> if (ops->vidioc_s_crop)
> return ops->vidioc_s_crop(file, fh, p);
> /* simulate capture crop using selection api */
>
> /* crop means compose for output devices */
> if (V4L2_TYPE_IS_OUTPUT(p->type))
> s.target = V4L2_SEL_TGT_COMPOSE_ACTIVE;
> else
> s.target = V4L2_SEL_TGT_CROP_ACTIVE;
>
> return ops->vidioc_s_selection(file, fh, &s);
> }
>
> i.e. it does exactly opposite to what we would expect for M2M.
You are right. Instead of handling this confusion in driver, as you
mentioned, we can use
vfl_dir field to select the target before sending it to the driver.
apart from using this vfl_dir field, I can't able to see any other
solution here.
Regards,
Shaik Ameer Basha
>
> One possible solution would be to get hold of struct video_device and
> do proper targets conversion after checking the vfl_dir field.
>
> Does anyone have suggestions on this ?
>
>
> BTW, we still have some V4L2_SEL_TGT*_ACTIVE symbols left, I'll write
> a patch to clean this up.
>
> [1] http://hverkuil.home.xs4all.nl/spec/media.html#idp9025504
> [2] http://hverkuil.home.xs4all.nl/spec/media.html#idp9031840
>
> --
> Thanks,
> Sylwester
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