media: Fix V4L2_COLORSPACE_470_SYSTEM_BG description

The description of the V4L2_COLORSPACE_470_SYSTEM_BG stated that it was
superseded by SMPTE 170M. That is incorrect. The probably root cause of
this is that the HDMI standard does not support this colorspace and,
unless otherwise signaled, will fall back to SMPTE 170M for SDTV.

However, EBU Tech. 3321 states that sources should signal Rec. 709 as the
colorimetry when using HDMI since the difference between Rec. 709 and
Tech. 3213 are negligible.

Update the text accordingly.

Also drop a spurious " at the end of the Tech 3213 title in the
bibliography.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/v4l/biblio.rst

@@ -270,7 +270,17 @@ EBU Tech 3213
 =============
 
 
-:title:     E.B.U. Standard for Chromaticity Tolerances for Studio Monitors"
+:title:     E.B.U. Standard for Chromaticity Tolerances for Studio Monitors
+
+:author:    European Broadcast Union (http://www.ebu.ch)
+
+.. _tech3321:
+
+EBU Tech 3321
+=============
+
+
+:title:     E.B.U. guidelines for Consumer Flat Panel Displays (FPDs)
 
 :author:    European Broadcast Union (http://www.ebu.ch)
 

Documentation/userspace-api/media/v4l/colorspaces-details.rst

@@ -674,8 +674,9 @@ Colorspace EBU Tech. 3213 (V4L2_COLORSPACE_470_SYSTEM_BG)
 =========================================================
 
 The :ref:`tech3213` standard defines the colorspace used by PAL/SECAM
-in 1975. In practice this colorspace is obsolete and SMPTE 170M should
-be used instead. The default transfer function is
+in 1975. Note that this colorspace is not supported by the HDMI interface.
+Instead :ref:`tech3321` recommends that Rec. 709 is used instead for HDMI.
+The default transfer function is
 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
 range. The chromaticities of the primary colors and the white reference

include/uapi/linux/videodev2.h

@@ -221,9 +221,7 @@ enum v4l2_colorspace {
 	V4L2_COLORSPACE_470_SYSTEM_M  = 5,
 
 	/*
-	 * EBU Tech 3213 PAL/SECAM colorspace. This only makes sense when
-	 * dealing with really old PAL/SECAM recordings. Superseded by
-	 * SMPTE 170M.
+	 * EBU Tech 3213 PAL/SECAM colorspace.
 	 */
 	V4L2_COLORSPACE_470_SYSTEM_BG = 6,