Add strobe duration and strobe output enable v4l2 ctrl

This series adds two new v4l2 controls:
- V4L2_CID_FLASH_DURATION: "Strobe duration": This control enables
  setting a desired flash/strobe length/duration in µs.
- V4L2_CID_FLASH_STROBE_OE: "Strobe output enable": This
  control enables the hardware strobe output signal of a v4l2 device.

As a first user of these new controls add basic flash/strobe support
for ov9282 sensors using their "hardware strobe output". The duration
calculation is only interpolated from various measurements, as no
documentation was found.

Further flash/strobe-related controls as well as a migration to v4l2-cci
helpers for ov9282 will likely be implemented in future series.

All register addresses/values are based on the OV9281 datasheet v1.53
(january 2019). This series was tested using an ov9281 VisionComponents
camera module.

Signed-off-by: Richard Leitner <richard.leitner@linux.dev>
---
Changes in v8:
- Minor styling changes across the set
- Add missing error handling for ov9282 strobe_frame_span writing
- Rename V4L2_CID_FLASH_HW_STROBE_SIGNAL to V4L2_CID_FLASH_STROBE_OE
- Drop 02/10: FLASH_DURATION handling in v4l2-flash
- Drop 08/10: strobe_source in ov9282
- Link to v7: https://lore.kernel.org/r/20250901-ov9282-flash-strobe-v7...

Changes in v7:
- Improved v4l2 uAPI documentation (thanks Sakari)
- Link to v6: https://lore.kernel.org/r/20250716-ov9282-flash-strobe-v6...

Changes in v6:
- Fix "Alignment should match open parenthesis" by Media-CI bot in v4l2-flash-led-class.c
- Fix "format string contains non-ascii character (µ)" by Media-CI bot in ov9282.c
- Introduce new V4L2_CID_FLASH_HW_STROBE_SIGNAL control (as suggested by Sakari)
- Implement V4L2_CID_FLASH_HW_STROBE_SIGNAL instead of
  V4L2_CID_FLASH_LED_MODE in ov9282.c (as suggested by Sakari)
- Drop "media: v4l2-flash: fix flash_timeout comment" as this was
  applied (thanks Lee)
- Link to v5: https://lore.kernel.org/r/20250617-ov9282-flash-strobe-v5...

Changes in v5:
- Improve try_ctrl for flash_duration by using DIV_ROUND_UP() and abs() (thanks Sakari)
- Drop "leds: flash: Add support for flash/strobe duration" as this was applied upstream
- Add "media: i2c: ov9282: dynamic flash_duration maximum" (thanks Sakari)
- Link to v4: https://lore.kernel.org/r/20250507-ov9282-flash-strobe-v4...

Changes in v4:
- Fix FLASH_DURATION implementation in v4l2-flash-led-class.c by adding a
  missing brace and enum entry (thanks Sakari)
- Fix format of multiline comment in ov9282.c (thanks Sakari)
- Add missing NULL check in ov9282.c (thanks Sakari)
- Adapt nr_of_controls_hint for v4l2 handler in ov9282.c (thanks Sakari)
- Add patch for implementing try_ctrl for strobe_duration (thanks Sakari)
- Link to v3: https://lore.kernel.org/r/20250429-ov9282-flash-strobe-v3...

Changes in v3:
- create separate patch for leds driver changes (thanks Lee)
- Link to v2: https://lore.kernel.org/r/20250314-ov9282-flash-strobe-v2...

Changes in v2:
- remove not needed controls in struct ov9282 (thanks Dave)
- Fix commit message of 3/3 regarding framerate get/set (thanks Dave)
- Add V4L2_CID_FLASH_STROBE_SOURCE impementation to ov9282
- Add new V4L2_CID_FLASH_DURATION control (as suggested by Laurent)
- Use FLASH_DURATION instead of FLASH_TIMEOUT for ov9282
- Link to v1: https://lore.kernel.org/r/20250303-ov9282-flash-strobe-v1...

---
Richard Leitner (8):
      media: v4l: ctrls: add a control for flash/strobe duration
      media: v4l: ctrls: add a control for enabling strobe output
      Documentation: uAPI: media: add V4L2_CID_FLASH_{DURATION,STROBE_OE}
      media: i2c: ov9282: add output enable register definitions
      media: i2c: ov9282: add strobe output enable v4l2 control
      media: i2c: ov9282: add strobe_duration v4l2 control
      media: i2c: ov9282: implement try_ctrl for strobe_duration
      media: i2c: ov9282: dynamic flash_duration maximum

 .../userspace-api/media/v4l/ext-ctrls-flash.rst    |  42 ++++++
 drivers/media/i2c/ov9282.c                         | 165 ++++++++++++++++++++-
 drivers/media/v4l2-core/v4l2-ctrls-defs.c          |   3 +
 include/uapi/linux/v4l2-controls.h                 |   2 +
 4 files changed, 206 insertions(+), 6 deletions(-)
---
base-commit: 2f112b1c25da9f5346c2261ed35c5b1e0b906471
change-id: 20250303-ov9282-flash-strobe-ac6bd00c9de6

Best regards,
--  
Richard Leitner <richard.leitner@linux.dev>