V4L/DVB (9191): ivtv: partially revert an earlier patch that checks t…

…he max image height

Ian Armstrong pointed out to me that it is perfectly valid to have a
576 lines YUV video with NTSC output in this particular case. In fact,
without this the X driver for ivtv does not function properly.

Reverted my earlier change that restrictred the height to 480 for NTSC
and add the comments provided by Ian to explain what is happening here.

Thanks-to: Ian Armstrong <ian@iarmst.co.uk>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/ivtv/ivtv-ioctl.c

@@ -509,15 +509,29 @@ static int ivtv_try_fmt_sliced_vbi_cap(struct file *file, void *fh, struct v4l2_
 static int ivtv_try_fmt_vid_out(struct file *file, void *fh, struct v4l2_format *fmt)
 {
 	struct ivtv_open_id *id = fh;
-	struct ivtv *itv = id->itv;
 	s32 w = fmt->fmt.pix.width;
 	s32 h = fmt->fmt.pix.height;
 	int field = fmt->fmt.pix.field;
 	int ret = ivtv_g_fmt_vid_out(file, fh, fmt);
 
 	w = min(w, 720);
 	w = max(w, 2);
-	h = min(h, itv->is_out_50hz ? 576 : 480);
+	/* Why can the height be 576 even when the output is NTSC?
+
+	   Internally the buffers of the PVR350 are always set to 720x576. The
+	   decoded video frame will always be placed in the top left corner of
+	   this buffer. For any video which is not 720x576, the buffer will
+	   then be cropped to remove the unused right and lower areas, with
+	   the remaining image being scaled by the hardware to fit the display
+	   area. The video can be scaled both up and down, so a 720x480 video
+	   can be displayed full-screen on PAL and a 720x576 video can be
+	   displayed without cropping on NTSC.
+
+	   Note that the scaling only occurs on the video stream, the osd
+	   resolution is locked to the broadcast standard and not scaled.
+
+	   Thanks to Ian Armstrong for this explanation. */
+	h = min(h, 576);
 	h = max(h, 2);
 	if (id->type == IVTV_DEC_STREAM_TYPE_YUV)
 		fmt->fmt.pix.field = field;