[PATCH AUTOSEL 6.17-5.15] media: adv7180: Do not write format to device in set_fmt

[Sasha Levin <sashal@kernel.org>]

From: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>

[ Upstream commit 46c1e7814d1c3310ef23c01ed1a582ef0c8ab1d2 ]

The .set_fmt callback should not write the new format directly do the
device, it should only store it and have it applied by .s_stream.

The .s_stream callback already calls adv7180_set_field_mode() so it's
safe to remove programming of the device and just store the format and
have .s_stream apply it.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.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

- Fixes incorrect behavior: The change enforces the V4L2 subdev rule
  that .set_fmt should not program hardware but only update state, with
  hardware programming deferred to .s_stream. In the new code, .set_fmt
  (driver’s `adv7180_set_pad_format`) only stores the requested field
  and does not touch the device, eliminating unintended runtime side
  effects during format negotiation. See
  `drivers/media/i2c/adv7180.c:784-793` where it now only assigns
  `state->field` for ACTIVE formats and no longer toggles power or
  programs registers.

- Safe because .s_stream already applies the format: The .s_stream path
  powers the device off, configures it, then powers it on, and
  explicitly applies the field mode. `adv7180_s_stream` calls
  `init_device` when enabling, which calls `adv7180_set_field_mode`.
  See:
  - `drivers/media/i2c/adv7180.c:927-955` (.s_stream powers off, calls
    `init_device`, powers on),
  - `drivers/media/i2c/adv7180.c:844-859` (`init_device` calls
    `adv7180_program_std` then `adv7180_set_field_mode` at
    `drivers/media/i2c/adv7180.c:854`).
  This guarantees the stored `state->field` is applied at the correct
time.

- Eliminates disruptive side effects: Previously, .set_fmt would power-
  cycle the decoder and program field mode immediately (via
  `adv7180_set_power(state, false)`, `adv7180_set_field_mode(state)`,
  `adv7180_set_power(state, true)`), which could:
  - Disrupt ongoing or prepared streaming sessions by unexpectedly
    toggling power during format negotiation.
  - Violate the expected V4L2 subdev semantics where format negotiation
    should be side-effect-free.
  The new behavior prevents these issues by staging only the state
change and deferring hardware ops to .s_stream.

- Consistency and correctness: The stored field influences both
  negotiated format reporting and hardware setup when streaming starts:
  - Format reporting uses `state->field` to compute height and field
    (see `drivers/media/i2c/adv7180.c:700-709` and `759-761`).
  - When powering on with CSI-2, `adv7180_set_power` also considers
    `state->field` (e.g., sets CSI register 0x1D if progressive output
    is used), ensuring consistent device programming once the stream
    starts (see `drivers/media/i2c/adv7180.c:202-219`).

- Contained change, minimal risk:
  - Single-file, localized change to adv7180 driver.
  - No new features or ABI changes; aligns with established subdev
    patterns.
  - No architectural shifts; only removes premature device programming
    from .set_fmt.
  - The driver already centralizes device programming within the
    streaming lifecycle, so behavior remains correct while avoiding
    premature side effects.

- Stable suitability:
  - Addresses a real behavioral bug (programming hardware during
    .set_fmt) that can lead to video glitches or races during
    negotiation.
  - Small, targeted patch that reduces side effects and adheres to V4L2
    best practices.
  - Low regression risk provided the target stable trees have the same
    pattern where .s_stream calls into `init_device` →
    `adv7180_set_field_mode` (as in this tree). In this codebase, that
    condition is satisfied.

Given these points, this is a good candidate for backporting to stable
media trees.

 drivers/media/i2c/adv7180.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/drivers/media/i2c/adv7180.c b/drivers/media/i2c/adv7180.c
index 84600fa75ae8a..8100fe6b0f1d4 100644
--- a/drivers/media/i2c/adv7180.c
+++ b/drivers/media/i2c/adv7180.c
@@ -812,14 +812,7 @@ static int adv7180_set_pad_format(struct v4l2_subdev *sd,
 	ret = adv7180_mbus_fmt(sd,  &format->format);
 
 	if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE) {
-		if (state->field != format->format.field) {
-			guard(mutex)(&state->mutex);
-
-			state->field = format->format.field;
-			adv7180_set_power(state, false);
-			adv7180_set_field_mode(state);
-			adv7180_set_power(state, true);
-		}
+		state->field = format->format.field;
 	} else {
 		framefmt = v4l2_subdev_state_get_format(sd_state, 0);
 		*framefmt = format->format;
-- 
2.51.0