media: Add Y012 video format

Y012 is a luma-only formats with 12-bits per pixel,
expanded to 16bits.
Data in the 12 high bits, zeros in the 4 low bits,
arranged in little endian order.
Signed-off-by: Ming Qian <ming.qian@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst

@@ -103,6 +103,17 @@ are often referred to as greyscale formats.
       - ...
       - ...
 
+    * .. _V4L2-PIX-FMT-Y012:
+
+      - ``V4L2_PIX_FMT_Y012``
+      - 'Y012'
+
+      - Y'\ :sub:`0`\ [3:0] `0000`
+      - Y'\ :sub:`0`\ [11:4]
+      - ...
+      - ...
+      - ...
+
     * .. _V4L2-PIX-FMT-Y14:
 
       - ``V4L2_PIX_FMT_Y14``
@@ -146,3 +157,7 @@ are often referred to as greyscale formats.
     than 16 bits. For example, 10 bits per pixel uses values in the range 0 to
     1023. For the IPU3_Y10 format 25 pixels are packed into 32 bytes, which
     leaves the 6 most significant bits of the last byte padded with 0.
+
+    For Y012 and Y12 formats, Y012 places its data in the 12 high bits, with
+    padding zeros in the 4 low bits, in contrast to the Y12 format, which has
+    its padding located in the most significant bits of the 16 bit word.

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

@@ -1303,6 +1303,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
 	case V4L2_PIX_FMT_Y6:		descr = "6-bit Greyscale"; break;
 	case V4L2_PIX_FMT_Y10:		descr = "10-bit Greyscale"; break;
 	case V4L2_PIX_FMT_Y12:		descr = "12-bit Greyscale"; break;
+	case V4L2_PIX_FMT_Y012:		descr = "12-bit Greyscale (bits 15-4)"; break;
 	case V4L2_PIX_FMT_Y14:		descr = "14-bit Greyscale"; break;
 	case V4L2_PIX_FMT_Y16:		descr = "16-bit Greyscale"; break;
 	case V4L2_PIX_FMT_Y16_BE:	descr = "16-bit Greyscale BE"; break;

include/uapi/linux/videodev2.h

@@ -586,6 +586,7 @@ struct v4l2_pix_format {
 #define V4L2_PIX_FMT_Y6      v4l2_fourcc('Y', '0', '6', ' ') /*  6  Greyscale     */
 #define V4L2_PIX_FMT_Y10     v4l2_fourcc('Y', '1', '0', ' ') /* 10  Greyscale     */
 #define V4L2_PIX_FMT_Y12     v4l2_fourcc('Y', '1', '2', ' ') /* 12  Greyscale     */
+#define V4L2_PIX_FMT_Y012    v4l2_fourcc('Y', '0', '1', '2') /* 12  Greyscale     */
 #define V4L2_PIX_FMT_Y14     v4l2_fourcc('Y', '1', '4', ' ') /* 14  Greyscale     */
 #define V4L2_PIX_FMT_Y16     v4l2_fourcc('Y', '1', '6', ' ') /* 16  Greyscale     */
 #define V4L2_PIX_FMT_Y16_BE  v4l2_fourcc_be('Y', '1', '6', ' ') /* 16  Greyscale BE  */