[PATCH v4 0/4] backlight: qcom-wled: Fix OVP IRQ imbalance and start from the hardware state

[David Heidelberg via B4 Relay <devnull+david.ixit.cz@kernel.org>]

The qcom-wled OVP interrupt is enabled at probe whenever the module is
already on, but the driver still believes the backlight is off, so the
first brightness update re-enables the interrupt and trips "Unbalanced
enable for IRQ". sdm845-mainline has carried a workaround for years and
Joel posted a flag-based version last October [1], which Konrad and
Daniel asked to be replaced by something that does not track the IRQ
state by hand.

Patch 1 is the drvdata fix I said I would drop after v3. The objection
was that it stored the wrong object, not that the fix was wrong, so it
is back with the right one stored.

Patch 2 is unrelated too and fell out of writing the readback: the WLED3
brightness register stride has been one byte instead of two since the
2019 restructuring, so multi-string pm8941 boards only program one
string correctly. Untested, I have no WLED3 board; it restores what
pm8941-wled.c did and matches the downstream leds-qpnp.c layout.

[1] https://lore.kernel.org/all/20251021-qcom-wled-fix-unbalanced-ovp-irq-enable-v2-1-7ff115b4ffe7@joelselvaraj.com/

Signed-off-by: David Heidelberg <david@ixit.cz>
---
Changes in v4:
- I applied the 0x10 fix too late, now it's fixed in the right commit.
  (Konrad)
- Right object stored in the drvdata. (Konrad)
- Set the drvdata next to the other wled fields instead  of next to the
  backlight device registration.
- Reworded the drvdata commit, the NULL dereference is in wled_remove(),
  the driver has no PM callbacks.
- Link to v3: https://patch.msgid.link/20260914-qcom-wled-backlight-v3-0-d69fe9843841@ixit.cz

Changes in v3:
- Fix typo 0x10 != 0b10. (Sashiko)
- Added fix for a unrelated issue, but since reported as critical, let's
  squeeze it:
  Missing platform_set_drvdata() in wled_probe() leads to a guaranteed NULL pointer dereference in wled_remove().
  (Sashiko)
- Link to v2: https://patch.msgid.link/20260914-qcom-wled-backlight-v2-0-a908d9233e93@ixit.cz

Changes in v2:
- Add a fix for the WLED3 brightness register stride.
- Add patch reading the programmed brightness back via
  backlight_ops.get_brightness. (Konrad)
- Note the brightness readback is done in the follow-up to the first
  patch.
- Link to v1: https://patch.msgid.link/20260908-qcom-wled-backlight-v1-1-c4dd4eabda07@ixit.cz

---
David Heidelberg (4):
      backlight: qcom-wled: Fix NULL pointer dereference in wled_remove()
      backlight: qcom-wled: Fix WLED3 brightness register stride
      backlight: qcom-wled: Fix unbalanced OVP IRQ enable at probe
      backlight: qcom-wled: Read back the programmed brightness at probe

 drivers/video/backlight/qcom-wled.c | 89 +++++++++++++++++++++++++++++++------
 1 file changed, 76 insertions(+), 13 deletions(-)
---
base-commit: 944a035ecca915ae947905dcfb03f2b9dc6d032c
change-id: 20260908-qcom-wled-backlight-fd9574027353

Best regards,
--  
David Heidelberg <david@ixit.cz>