[media] videodev2.h: add support for transfer functions

In the past the transfer function was implied by the colorspace. However,
it is an independent entity in its own right. Add support for explicitly
choosing the transfer function.

This change will allow us to represent linear RGB (as is used by openGL), and
it will make it easier to work with decoded video material since most codecs
store the transfer function as a separate property as well.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

2 files changed, 43 insertions, 2 deletions

diff --git a/include/uapi/linux/v4l2-mediabus.h b/include/uapi/linux/v4l2-mediabus.h
index 26db20647e6f..9cac6325cc7e 100644
--- a/include/uapi/linux/v4l2-mediabus.h
+++ b/include/uapi/linux/v4l2-mediabus.h
@@ -24,6 +24,7 @@
  * @colorspace: colorspace of the data (from enum v4l2_colorspace)
  * @ycbcr_enc:  YCbCr encoding of the data (from enum v4l2_ycbcr_encoding)
  * @quantization: quantization of the data (from enum v4l2_quantization)
+ * @xfer_func:  transfer function of the data (from enum v4l2_xfer_func)
  */
 struct v4l2_mbus_framefmt {
         __u32                   width;
@@ -33,7 +34,8 @@ struct v4l2_mbus_framefmt {
         __u32                   colorspace;
         __u16                   ycbcr_enc;
         __u16                   quantization;
-        __u32                   reserved[6];
+        __u16                   xfer_func;
+        __u16                   reserved[11];
 };
 
 #ifndef __KERNEL__
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 003a91292a4f..3d5fc72d53a7 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -240,6 +240,42 @@ enum v4l2_colorspace {
         ((is_sdtv) ? V4L2_COLORSPACE_SMPTE170M : \
          ((is_hdtv) ? V4L2_COLORSPACE_REC709 : V4L2_COLORSPACE_SRGB))
 
+enum v4l2_xfer_func {
+        /*
+         * Mapping of V4L2_XFER_FUNC_DEFAULT to actual transfer functions
+         * for the various colorspaces:
+         *
+         * V4L2_COLORSPACE_SMPTE170M, V4L2_COLORSPACE_470_SYSTEM_M,
+         * V4L2_COLORSPACE_470_SYSTEM_BG, V4L2_COLORSPACE_REC709 and
+         * V4L2_COLORSPACE_BT2020: V4L2_XFER_FUNC_709
+         *
+         * V4L2_COLORSPACE_SRGB, V4L2_COLORSPACE_JPEG: V4L2_XFER_FUNC_SRGB
+         *
+         * V4L2_COLORSPACE_ADOBERGB: V4L2_XFER_FUNC_ADOBERGB
+         *
+         * V4L2_COLORSPACE_SMPTE240M: V4L2_XFER_FUNC_SMPTE240M
+         *
+         * V4L2_COLORSPACE_RAW: V4L2_XFER_FUNC_NONE
+         */
+        V4L2_XFER_FUNC_DEFAULT     = 0,
+        V4L2_XFER_FUNC_709         = 1,
+        V4L2_XFER_FUNC_SRGB        = 2,
+        V4L2_XFER_FUNC_ADOBERGB    = 3,
+        V4L2_XFER_FUNC_SMPTE240M   = 4,
+        V4L2_XFER_FUNC_NONE        = 5,
+};
+
+/*
+ * Determine how XFER_FUNC_DEFAULT should map to a proper transfer function.
+ * This depends on the colorspace.
+ */
+#define V4L2_MAP_XFER_FUNC_DEFAULT(colsp) \
+        ((colsp) == V4L2_XFER_FUNC_ADOBERGB ? V4L2_XFER_FUNC_ADOBERGB : \
+         ((colsp) == V4L2_COLORSPACE_SMPTE240M ? V4L2_XFER_FUNC_SMPTE240M : \
+          ((colsp) == V4L2_COLORSPACE_RAW ? V4L2_XFER_FUNC_NONE : \
+           ((colsp) == V4L2_COLORSPACE_SRGB || (colsp) == V4L2_COLORSPACE_JPEG ? \
+            V4L2_XFER_FUNC_SRGB : V4L2_XFER_FUNC_709))))
+
 enum v4l2_ycbcr_encoding {
         /*
          * Mapping of V4L2_YCBCR_ENC_DEFAULT to actual encodings for the
@@ -409,6 +445,7 @@ struct v4l2_pix_format {
         __u32                   flags;          /* format flags (V4L2_PIX_FMT_FLAG_*) */
         __u32                   ycbcr_enc;      /* enum v4l2_ycbcr_encoding */
         __u32                   quantization;   /* enum v4l2_quantization */
+        __u32                   xfer_func;      /* enum v4l2_xfer_func */
 };
 
 /*      Pixel format         FOURCC                          depth  Description  */
@@ -1907,6 +1944,7 @@ struct v4l2_plane_pix_format {
  * @flags:              format flags (V4L2_PIX_FMT_FLAG_*)
  * @ycbcr_enc:          enum v4l2_ycbcr_encoding, Y'CbCr encoding
  * @quantization:       enum v4l2_quantization, colorspace quantization
+ * @xfer_func:          enum v4l2_xfer_func, colorspace transfer function
  */
 struct v4l2_pix_format_mplane {
         __u32                           width;
@@ -1920,7 +1958,8 @@ struct v4l2_pix_format_mplane {
         __u8                            flags;
         __u8                            ycbcr_enc;
         __u8                            quantization;
-        __u8                            reserved[8];
+        __u8                            xfer_func;
+        __u8                            reserved[7];
 } __attribute__ ((packed));
 
 /**