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media: v4l2-ctrl: Add a comment on why we zero out compound controls fields 

Since it's not necessarily very explicit why we need to zero some fields
in std_validate_compound, add a comment before the function to explain
why, which should help as a reminder.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
This commit is contained in:
Paul Kocialkowski 2019-07-25 14:55:59 -04:00 committed by Mauro Carvalho Chehab
parent 4b4d62b031
commit 1e42d384aa
1 changed files with 4 additions and 0 deletions
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4
drivers/media/v4l2-core/v4l2-ctrls.c
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@ -1645,6 +1645,10 @@ static void std_log(const struct v4l2_ctrl *ctrl)
#define zero_padding(s) \
memset(&(s).padding, 0, sizeof((s).padding))
/*
* Compound controls validation requires setting unused fields/flags to zero
* in order to properly detect unchanged controls with std_equal's memcmp.
*/
static int std_validate_compound(const struct v4l2_ctrl *ctrl, u32 idx,
union v4l2_ctrl_ptr ptr)
{