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[media] DocBook v4l: update bytesperline handling 

The documentation says that the bytesperline field in v4l2_pix_format refers
to the largest plane in the case of planar formats (i.e. multiple planes
stores in a single buffer).

For almost all planar formats the first plane is also the largest (or equal)
plane, except for two formats: V4L2_PIX_FMT_NV24/NV42. For this YUV 4:4:4
format the second chroma plane is twice the size of the first luma plane.

Looking at the very few drivers that support this format the bytesperline
value that they report is actually that of the first plane and not that
of the largest plane.

Rather than fixing the drivers it makes more sense to update the documentation
since it is very difficult to use the largest plane for this. You would have
to check what the format is in order to know to which plane bytesperline
belongs, which makes calculations much more difficult.

This patch updates the documentation accordingly.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
This commit is contained in:
Hans Verkuil 2015-03-11 09:00:45 -03:00 committed by Mauro Carvalho Chehab
parent 3259aa57db
commit 2ddb77bb11
2 changed files with 4 additions and 4 deletions
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4
Documentation/DocBook/media/v4l/pixfmt.xml
View File

@ -80,9 +80,9 @@ padding bytes after the last line of an image cross a system page
boundary. Input devices may write padding bytes, the value is
undefined. Output devices ignore the contents of padding
bytes.</para><para>When the image format is planar the
<structfield>bytesperline</structfield> value applies to the largest
<structfield>bytesperline</structfield> value applies to the first
plane and is divided by the same factor as the
<structfield>width</structfield> field for any smaller planes. For
<structfield>width</structfield> field for the other planes. For
example the Cb and Cr planes of a YUV 4:2:0 image have half as many
padding bytes following each line as the Y plane. To avoid ambiguities
drivers must return a <structfield>bytesperline</structfield> value

4
Documentation/DocBook/media/v4l/vidioc-g-fbuf.xml
View File

@ -240,9 +240,9 @@ where padding bytes after the last line of an image cross a system
page boundary. Capture devices may write padding bytes, the value is
undefined. Output devices ignore the contents of padding
bytes.</para><para>When the image format is planar the
<structfield>bytesperline</structfield> value applies to the largest
<structfield>bytesperline</structfield> value applies to the first
plane and is divided by the same factor as the
<structfield>width</structfield> field for any smaller planes. For
<structfield>width</structfield> field for the other planes. For
example the Cb and Cr planes of a YUV 4:2:0 image have half as many
padding bytes following each line as the Y plane. To avoid ambiguities
drivers must return a <structfield>bytesperline</structfield> value