media: v4l: subdev: Add pre_streamon and post_streamoff callbacks

Add pre_streamon and post_streamoff callbacks that can be used to set a
CSI-2 transmitter to LP-11 or LP-111 mode. This can be used by receiver
drivers to reliably initialise the receiver when its initialisation
requires software involvement.
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab+huawei@kernel.org>

include/media/v4l2-subdev.h

@@ -354,6 +354,16 @@ struct v4l2_mbus_frame_desc {
 	unsigned short num_entries;
 };
 
+/**
+ * enum v4l2_subdev_pre_streamon_flags - Flags for pre_streamon subdev core op
+ *
+ * @V4L2_SUBDEV_PRE_STREAMON_FL_MANUAL_LP: Set the transmitter to either LP-11
+ *	or LP-111 mode before call to s_stream().
+ */
+enum v4l2_subdev_pre_streamon_flags {
+	V4L2_SUBDEV_PRE_STREAMON_FL_MANUAL_LP = BIT(0),
+};
+
 /**
  * struct v4l2_subdev_video_ops - Callbacks used when v4l device was opened
  *				  in video mode.
@@ -409,6 +419,19 @@ struct v4l2_mbus_frame_desc {
  * @s_rx_buffer: set a host allocated memory buffer for the subdev. The subdev
  *	can adjust @size to a lower value and must not write more data to the
  *	buffer starting at @data than the original value of @size.
+ *
+ * @pre_streamon: May be called before streaming is actually started, to help
+ *	initialising the bus. Current usage is to set a CSI-2 transmitter to
+ *	LP-11 or LP-111 mode before streaming. See &enum
+ *	v4l2_subdev_pre_streamon_flags.
+ *
+ *	pre_streamon shall return error if it cannot perform the operation as
+ *	indicated by the flags argument. In particular, -EACCES indicates lack
+ *	of support for the operation. The caller shall call post_streamoff for
+ *	each successful call of pre_streamon.
+ *
+ * @post_streamoff: Called after streaming is stopped, but if and only if
+ *	pre_streamon was called earlier.
  */
 struct v4l2_subdev_video_ops {
 	int (*s_routing)(struct v4l2_subdev *sd, u32 input, u32 output, u32 config);
@@ -435,6 +458,8 @@ struct v4l2_subdev_video_ops {
 			struct v4l2_dv_timings *timings);
 	int (*s_rx_buffer)(struct v4l2_subdev *sd, void *buf,
 			   unsigned int *size);
+	int (*pre_streamon)(struct v4l2_subdev *sd, u32 flags);
+	int (*post_streamoff)(struct v4l2_subdev *sd);
 };
 
 /**