[media] v4l: Document raw bayer 4CC codes

Document guidelines how 4CC codes should be named. Only raw bayer is
included currently. Other formats should be documented later on.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

diff --git a/Documentation/video4linux/4CCs.txt b/Documentation/video4linux/4CCs.txt
new file mode 100644 (file)
index 0000000..41241af
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+++ b/Documentation/video4linux/4CCs.txt
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+Guidelines for Linux4Linux pixel format 4CCs
+============================================
+
+Guidelines for Video4Linux 4CC codes defined using v4l2_fourcc() are
+specified in this document. First of the characters defines the nature of
+the pixel format, compression and colour space. The interpretation of the
+other three characters depends on the first one.
+
+Existing 4CCs may not obey these guidelines.
+
+Formats
+=======
+
+Raw bayer
+---------
+
+The following first characters are used by raw bayer formats:
+
+       B: raw bayer, uncompressed
+       b: raw bayer, DPCM compressed
+       a: A-law compressed
+       u: u-law compressed
+
+2nd character: pixel order
+       B: BGGR
+       G: GBRG
+       g: GRBG
+       R: RGGB
+
+3rd character: uncompressed bits-per-pixel 0--9, A--
+
+4th character: compressed bits-per-pixel 0--9, A--