[PATCH AUTOSEL 6.17-6.12] media: pci: mgb4: Fix timings comparison in VIDIOC_S_DV_TIMINGS

[Sasha Levin <sashal@kernel.org>]

From: Martin Tůma <martin.tuma@digiteqautomotive.com>

[ Upstream commit 0750649b528ff18d1d68aecb45b34ec22d5ab778 ]

Compare the whole v4l2_bt_timings struct, not just the width/height when
setting new timings. Timings with the same resolution and different
pixelclock can now be properly set.

Signed-off-by: Martin Tůma <martin.tuma@digiteqautomotive.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES

- What it fixes: Prevents a real functional bug where setting DV timings
  with the same width/height but different pixelclock (or other BT
  fields) was treated as “no change” and ignored. This blocked valid
  timing changes (e.g., framerate changes at the same resolution).
- Code change: Replaces a narrow equality check on resolution with a
  full DV timings comparison:
  - New check: `v4l2_match_dv_timings(timings, &vindev->timings, 0,
    false)` in `drivers/media/pci/mgb4/mgb4_vin.c:613`.
  - Old behavior (implicit from the diff): only compared `width` and
    `height`, causing false “match” for differing
    pixelclock/porches/polarities/etc.
- Correct behavior when busy: With the fix, if the queue is streaming
  and the requested timings differ in any BT field,
  `vidioc_s_dv_timings` returns `-EBUSY` instead of silently returning 0
  while not applying the change (see `vb2_is_busy` branch right after
  the match check in `drivers/media/pci/mgb4/mgb4_vin.c:615`).
- Scope and risk: Minimal and contained (one-line logic change in a
  single driver). No API/ABI change, no architectural impact, only
  affects `VIDIOC_S_DV_TIMINGS` behavior in the MGB4 capture driver.
- Uses a proven helper: `v4l2_match_dv_timings` is the standard V4L2
  helper that compares the full `v4l2_bt_timings` including
  width/height, interlaced, polarities, pixelclock (with tolerance),
  porches, vsync, flags, and interlaced-specific fields; see
  implementation at `drivers/media/v4l2-core/v4l2-dv-timings.c:267`.
  This pattern is used across other drivers.
- User impact: Enables setting legitimate timings that share resolution
  but differ in pixelclock (and other BT parameters). Previously such
  requests were incorrectly treated as no-ops.
- Stable criteria fit:
  - Important bugfix affecting real use (DV timings changes ignored).
  - Small, localized change with low regression risk.
  - No new features or interface changes.
  - Touches only a non-core driver
    (`drivers/media/pci/mgb4/mgb4_vin.c`).
- Backport note: Apply to stable kernels that include the MGB4 driver;
  the helper `v4l2_match_dv_timings` is long-standing in V4L2 and does
  not introduce dependencies.

Overall, this is a low-risk, clear bug fix that improves correctness and
user experience when changing DV timings; it should be backported.

 drivers/media/pci/mgb4/mgb4_vin.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/media/pci/mgb4/mgb4_vin.c b/drivers/media/pci/mgb4/mgb4_vin.c
index 989e93f67f75b..42c327bc50e10 100644
--- a/drivers/media/pci/mgb4/mgb4_vin.c
+++ b/drivers/media/pci/mgb4/mgb4_vin.c
@@ -610,8 +610,7 @@ static int vidioc_s_dv_timings(struct file *file, void *fh,
 	    timings->bt.height < video_timings_cap.bt.min_height ||
 	    timings->bt.height > video_timings_cap.bt.max_height)
 		return -EINVAL;
-	if (timings->bt.width == vindev->timings.bt.width &&
-	    timings->bt.height == vindev->timings.bt.height)
+	if (v4l2_match_dv_timings(timings, &vindev->timings, 0, false))
 		return 0;
 	if (vb2_is_busy(&vindev->queue))
 		return -EBUSY;
-- 
2.51.0