When using VIDIOC_G_EDID there is a special case where start_blocks and
blocks are both set to 0. In that case the driver just has to set blocks to
the total number of available blocks and return 0.
Even though the drivers do this right and v4l2-compliance tests for it, it
turned out not to be documented in the spec. Fix this.
Signed-off-by: Hans Verkuil <hans.verk...@cisco.com>
Reported-by: Mats Randgaard <matra...@cisco.com>
diff --git a/Documentation/DocBook/media/v4l/vidioc-g-edid.xml
b/Documentation/DocBook/media/v4l/vidioc-g-edid.xml
index 6df40db..e44340c 100644
--- a/Documentation/DocBook/media/v4l/vidioc-g-edid.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-g-edid.xml
@@ -82,6 +82,13 @@
<para>If blocks have to be retrieved from the sink, then this call will
block until they
have been read.</para>
+ <para>If <structfield>start_block</structfield> and
<structfield>blocks</structfield> are
+ both set to 0 when <constant>VIDIOC_G_EDID</constant> is called, then the
driver will
+ set <structfield>blocks</structfield> to the total number of available
EDID blocks
+ and it will return 0 without copying any data. This is an easy way to
discover how many
+ EDID blocks there are. Note that if there are no EDID blocks available at
all, then
+ the driver will set <structfield>blocks</structfield> to 0 and it returns
0.</para>
+
<para>To set the EDID blocks of a receiver the application has to fill in
the <structfield>pad</structfield>,
<structfield>blocks</structfield> and <structfield>edid</structfield>
fields and set
<structfield>start_block</structfield> to 0. It is not possible to set
part of an EDID,
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