[PATCH v7 1/4] media: v4l2-ctrl: Add a comment on why we zero out compound controls fields

[Paul Kocialkowski]

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 at bootlin.com>
---
 drivers/media/v4l2-core/v4l2-ctrls.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
index 76fa2db0e8fb..cd1ae016706f 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -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)
 {
-- 
2.22.0