media: staging: ipu3-imgu: clarify the limitation of grid config

There are some grid configuration limitations for ImgU, which was
not described clearly in current uAPI header file, add the description
to help user to set the grid configuration correctly.
Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/staging/media/ipu3/include/uapi/intel-ipu3.h

@@ -34,11 +34,17 @@
  * struct ipu3_uapi_grid_config - Grid plane config
  *
  * @width:	Grid horizontal dimensions, in number of grid blocks(cells).
+ *		For AWB, the range is (16, 80).
+ *		For AF/AE, the range is (16, 32).
  * @height:	Grid vertical dimensions, in number of grid cells.
+ *		For AWB, the range is (16, 60).
+ *		For AF/AE, the range is (16, 24).
  * @block_width_log2:	Log2 of the width of each cell in pixels.
- *			for (2^3, 2^4, 2^5, 2^6, 2^7), values [3, 7].
+ *			For AWB, the range is [3, 6].
+ *			For AF/AE, the range is [3, 7].
  * @block_height_log2:	Log2 of the height of each cell in pixels.
- *			for (2^3, 2^4, 2^5, 2^6, 2^7), values [3, 7].
+ *			For AWB, the range is [3, 6].
+ *			For AF/AE, the range is [3, 7].
  * @height_per_slice:	The number of blocks in vertical axis per slice.
  *			Default 2.
  * @x_start: X value of top left corner of Region of Interest(ROI).