[PATCH v3 00/11] hwmon: chipcap2: various bug fixes

[Javier Carrasco <javier.carrasco.cruz@gmail.com>]

The original issue (race condition for the alarms) was found by Sashiko[1]
when an unrelated patch affected chipcap2.c. The issue is real as the
access to the variables is not protected by any locking mechanism
although 2 different sources (threaded interrupts and sysfs) could
modify them.

In further iterations Sashiko found new issues[2] that have been added to
the series:

- Fix be16 data handling.
- Defer probe when the IRQs are not available yet.
- IRQ teardown ordering: split the current implementation to provide the
  available interrupts before registering the hwmon device, and register
  the IRQs after the hwmon device has been registered.
- Disable the device after the hwmon device has been unregistered.
- Enable IRQ processing when the regulator is already enabled.
- Balance regulator counter.
- Do not discard the pending alarms when the device is disabled.
- Reset the completion to account for counter > 1.
- IRQ serialization and synchronization.

The last item required a dedicated mutex because the hwmon_lock was not
suitable to close the gaps where an interrupt might go unnoticed because
there is some dependency between the data read and the interrupt
generation, and also in the completion mechanism. I went through the
different alternatives with a combination of local Sashiko and a second
AI agent, and discarded some complex solutions to close gaps that are
more theoretical than practical e.g. the interrupt was fired, but it did
not reach the controller due to nested GPIO expanders. I added the
Assisted-by: tags to those patches accordingly, although it seems that
this requirement will soon vanish.

Additionally, a harmless off-by-one in a for loop has been fixed to save
~80 ms after the last failed command retry, and the error reporting has
been fixed to show the right issue. These two ones have not been tagged
for stable as they are only meant to improve reaction time and logging
inaccuracies after a command fails. The deferred probe does not have the
stable tag as it is just a reaction if interrupts were provided but
still not available. Of course, I can add the tags to all patches
if required.

The fixes have been validated on real hardware with an Amphenol
ChipCap 2 CC2D23S sensor.

[1] Link: https://lore.kernel.org/linux-hwmon/20260625162114.417EA1F000E9@smtp.kernel.org/
[2] Link: https://lore.kernel.org/linux-hwmon/20260821093706.D1EB11F000E9@smtp.kernel.org/

To: Guenter Roeck <linux@roeck-us.net>
Cc: linux-hwmon@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>

Changes in v3:
- Use a dedicated mutex instead of the hwmon subsystem lock to serialize
  the access to the alarm indicators, which no longer blocks the alarm
  handlers behind a sysfs read.
- New patch: do not discard the pending alarms on disable.
- New patch: synchronize the ready IRQ state.
- Register the data ready IRQ before registering the hwmon device (its
  handler does not use hwmon).
- Split the fixes into one patch per issue.
- Drop the patch to fix the channels in the humidity alarm
  notifications, which is already applied.
- Link to v2: https://lore.kernel.org/r/20260823-chipcap2_locks-v2-0-6a26c8e9e2fc@gmail.com

Changes in v2:
- Add fixes to the new issues reported by Sashiko.
- Use hwmon subsystem lock.
- Link to v1: https://lore.kernel.org/r/20260821-chipcap2_locks-v1-1-1d8ccabfc1b2@gmail.com

---
Javier Carrasco (11):
      hwmon: chipcap2: fix command error diagnostics
      hwmon: chipcap2: fix off-by-one in command mode retry loop
      hwmon: chipcap2: fix be16 handling
      hwmon: chipcap2: defer probe when IRQs are unavailable
      hwmon: chipcap2: fix IRQ teardown ordering
      hwmon: chipcap2: disable device after hwmon teardown
      hwmon: chipcap2: enable IRQ processing when regulator is already enabled
      hwmon: chipcap2: balance regulator state
      hwmon: chipcap2: do not discard pending alarms on disable
      hwmon: chipcap2: serialize access to the alarm indicators
      hwmon: chipcap2: synchronize ready IRQ state

 drivers/hwmon/chipcap2.c | 192 +++++++++++++++++++++++++++++++----------------
 1 file changed, 128 insertions(+), 64 deletions(-)
---
base-commit: 3857c2fe5449541e24afc5efdb0f81a8a8f9a3a0
change-id: 20260820-chipcap2_locks-c01013a24a0c

Best regards,
-- 
Javier Carrasco <javier.carrasco.cruz@gmail.com>