media: uvcvideo: Probe the PLF characteristics

The UVC 1.5 standard defines 4 values for the PLF control: Off, 50Hz,
60Hz and Auto. But it does not clearly define if all the values must be
implemented or not.

Instead of just using the UVC version to determine what the PLF control
can do, probe it.
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>

drivers/media/usb/uvc/uvc_ctrl.c

@@ -498,10 +498,53 @@ static const struct uvc_control_mapping uvc_ctrl_power_line_mapping_uvc15 = {
 static const struct uvc_control_mapping *uvc_ctrl_filter_plf_mapping(
 	struct uvc_video_chain *chain, struct uvc_control *ctrl)
 {
+	const struct uvc_control_mapping *out_mapping =
+					&uvc_ctrl_power_line_mapping_uvc11;
+	u8 *buf __free(kfree) = NULL;
+	u8 init_val;
+	int ret;
+
+	buf = kmalloc(sizeof(*buf), GFP_KERNEL);
+	if (!buf)
+		return NULL;
+
+	/* Save the current PLF value, so we can restore it. */
+	ret = uvc_query_ctrl(chain->dev, UVC_GET_CUR, ctrl->entity->id,
+			     chain->dev->intfnum, ctrl->info.selector,
+			     buf, sizeof(*buf));
+	/* If we cannot read the control skip it. */
+	if (ret)
+		return NULL;
+	init_val = *buf;
+
+	/* If PLF value cannot be set to off, it is limited. */
+	*buf = V4L2_CID_POWER_LINE_FREQUENCY_DISABLED;
+	ret = uvc_query_ctrl(chain->dev, UVC_SET_CUR, ctrl->entity->id,
+			     chain->dev->intfnum, ctrl->info.selector,
+			     buf, sizeof(*buf));
+	if (ret)
+		return &uvc_ctrl_power_line_mapping_limited;
+
+	/* UVC 1.1 does not define auto, we can exit. */
 	if (chain->dev->uvc_version < 0x150)
-		return &uvc_ctrl_power_line_mapping_uvc11;
-	else
-		return &uvc_ctrl_power_line_mapping_uvc15;
+		goto end;
+
+	/* Check if the device supports auto. */
+	*buf = V4L2_CID_POWER_LINE_FREQUENCY_AUTO;
+	ret = uvc_query_ctrl(chain->dev, UVC_SET_CUR, ctrl->entity->id,
+			     chain->dev->intfnum, ctrl->info.selector,
+			     buf, sizeof(*buf));
+	if (!ret)
+		out_mapping = &uvc_ctrl_power_line_mapping_uvc15;
+
+end:
+	/* Restore initial value and add mapping. */
+	*buf = init_val;
+	uvc_query_ctrl(chain->dev, UVC_SET_CUR, ctrl->entity->id,
+		       chain->dev->intfnum, ctrl->info.selector,
+		       buf, sizeof(*buf));
+
+	return out_mapping;
 }
 
 static const struct uvc_control_mapping uvc_ctrl_mappings[] = {