media: v4l: Add a UVC Metadata format

Add a pixel format, used by the UVC driver to stream metadata.

Signed-off-by: Guennadi Liakhovetski <[e-mail]>
Signed-off-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/media/uapi/v4l/meta-formats.rst

···
 .. toctree::
     :maxdepth: 1
 
+    pixfmt-meta-uvc
     pixfmt-meta-vsp1-hgo
     pixfmt-meta-vsp1-hgt

Documentation/media/uapi/v4l/pixfmt-meta-uvc.rst

···
+.. -*- coding: utf-8; mode: rst -*-
+
+.. _v4l2-meta-fmt-uvc:
+
+*******************************
+V4L2_META_FMT_UVC ('UVCH')
+*******************************
+
+UVC Payload Header Data
+
+
+Description
+===========
+
+This format describes standard UVC metadata, extracted from UVC packet headers
+and provided by the UVC driver through metadata video nodes. That data includes
+exact copies of the standard part of UVC Payload Header contents and auxiliary
+timing information, required for precise interpretation of timestamps, contained
+in those headers. See section "2.4.3.3 Video and Still Image Payload Headers" of
+the "UVC 1.5 Class specification" for details.
+
+Each UVC payload header can be between 2 and 12 bytes large. Buffers can
+contain multiple headers, if multiple such headers have been transmitted by the
+camera for the respective frame. However, the driver may drop headers when the
+buffer is full, when they contain no useful information (e.g. those without the
+SCR field or with that field identical to the previous header), or generally to
+perform rate limiting when the device sends a large number of headers.
+
+Each individual block contains the following fields:
+
+.. flat-table:: UVC Metadata Block
+    :widths: 1 4
+    :header-rows:  1
+    :stub-columns: 0
+
+    * - Field
+      - Description
+    * - __u64 ts;
+      - system timestamp in host byte order, measured by the driver upon
+        reception of the payload
+    * - __u16 sof;
+      - USB Frame Number in host byte order, also obtained by the driver as
+        close as possible to the above timestamp to enable correlation between
+        them
+    * - :cspan:`1` *The rest is an exact copy of the UVC payload header:*
+    * - __u8 length;
+      - length of the rest of the block, including this field
+    * - __u8 flags;
+      - Flags, indicating presence of other standard UVC fields
+    * - __u8 buf[];
+      - The rest of the header, possibly including UVC PTS and SCR fields

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

···
 	case V4L2_TCH_FMT_TU08:		descr = "8-bit unsigned touch data"; break;
 	case V4L2_META_FMT_VSP1_HGO:	descr = "R-Car VSP1 1-D Histogram"; break;
 	case V4L2_META_FMT_VSP1_HGT:	descr = "R-Car VSP1 2-D Histogram"; break;
+	case V4L2_META_FMT_UVC:		descr = "UVC payload header metadata"; break;
 
 	default:
 		/* Compressed formats */

include/uapi/linux/videodev2.h

···
 /* Meta-data formats */
 #define V4L2_META_FMT_VSP1_HGO    v4l2_fourcc('V', 'S', 'P', 'H') /* R-Car VSP1 1-D Histogram */
 #define V4L2_META_FMT_VSP1_HGT    v4l2_fourcc('V', 'S', 'P', 'T') /* R-Car VSP1 2-D Histogram */
+#define V4L2_META_FMT_UVC         v4l2_fourcc('U', 'V', 'C', 'H') /* UVC Payload Header metadata */
 
 /* priv field value to indicates that subsequent fields are valid. */
 #define V4L2_PIX_FMT_PRIV_MAGIC		0xfeedcafe