media: v4l: common: v4l2_get_link_freq: add printing a warning

Print a warning if V4L2_CID_LINK_FREQ control is not implemented.
Signed-off-by: Andrey Konovalov <andrey.konovalov@linaro.org>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/v4l2-core/v4l2-common.c

@@ -469,6 +469,11 @@ s64 v4l2_get_link_freq(struct v4l2_ctrl_handler *handler, unsigned int mul,
 			return -ENOENT;
 
 		freq = div_u64(v4l2_ctrl_g_ctrl_int64(ctrl) * mul, div);
+
+		pr_warn("%s: Link frequency estimated using pixel rate: result might be inaccurate\n",
+			__func__);
+		pr_warn("%s: Consider implementing support for V4L2_CID_LINK_FREQ in the transmitter driver\n",
+			__func__);
 	}
 
 	return freq > 0 ? freq : -EINVAL;