media: common: saa7146: fix compliance problems with field handling

The initial field value of the format is ANY, which isn't allowed.
Change to INTERLACED.

VIDIOC_TRY_FMT will overwrite vv->last_field, which is an
unwanted side-effect, so drop this.

And finally vidioc_s_fmt_vid_cap didn't initialize vv->last_field
correctly.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/common/saa7146/saa7146_fops.c

@@ -298,7 +298,7 @@ int saa7146_vv_init(struct saa7146_dev* dev, struct saa7146_ext_vv *ext_vv)
 	fmt->width = 384;
 	fmt->height = 288;
 	fmt->pixelformat = V4L2_PIX_FMT_BGR24;
-	fmt->field = V4L2_FIELD_ANY;
+	fmt->field = V4L2_FIELD_INTERLACED;
 	fmt->colorspace = V4L2_COLORSPACE_SMPTE170M;
 	fmt->bytesperline = 3 * fmt->width;
 	fmt->sizeimage = fmt->bytesperline * fmt->height;

drivers/media/common/saa7146/saa7146_video.c

@@ -381,20 +381,13 @@ static int vidioc_try_fmt_vid_cap(struct file *file, void *fh, struct v4l2_forma
 	}
 	switch (field) {
 	case V4L2_FIELD_ALTERNATE:
-		vv->last_field = V4L2_FIELD_TOP;
-		maxh = maxh / 2;
-		break;
 	case V4L2_FIELD_TOP:
 	case V4L2_FIELD_BOTTOM:
-		vv->last_field = V4L2_FIELD_INTERLACED;
 		maxh = maxh / 2;
 		break;
-	case V4L2_FIELD_INTERLACED:
-		vv->last_field = V4L2_FIELD_INTERLACED;
-		break;
 	default:
-		DEB_D("no known field mode '%d'\n", field);
-		return -EINVAL;
+		field = V4L2_FIELD_INTERLACED;
+		break;
 	}
 
 	f->fmt.pix.field = field;
@@ -434,6 +427,14 @@ static int vidioc_s_fmt_vid_cap(struct file *file, void *fh, struct v4l2_format
 	err = vidioc_try_fmt_vid_cap(file, fh, f);
 	if (0 != err)
 		return err;
+	switch (f->fmt.pix.field) {
+	case V4L2_FIELD_ALTERNATE:
+		vv->last_field = V4L2_FIELD_TOP;
+		break;
+	default:
+		vv->last_field = V4L2_FIELD_INTERLACED;
+		break;
+	}
 	vv->video_fmt = f->fmt.pix;
 	DEB_EE("set to pixelformat '%4.4s'\n",
 	       (char *)&vv->video_fmt.pixelformat);