[PATCH v5 0/3] hwmon: (applesmc) Convert to hwmon_device_register_with_info

[Shih-Yuan Lee <fourdollars@debian.org>]

Hi Guenter, Armin, and Henrik,

This is v5 of the patch series converting the applesmc driver from using
the deprecated hwmon_device_register() function to the modern
hwmon_device_register_with_info() API.

Changes in v5:
- Split the refactoring into a 3-patch logical series:
  - Patch 1: Cache fan positions during register initialization (preparatory).
  - Patch 2: Fix a pre-existing concurrency bug in lockless cache validation
             by introducing proper memory barriers (smp_load_acquire and
             smp_store_release) with checkpatch-compliant comments.
  - Patch 3: Convert the driver to the modern HWMON API.
- Address Sashiko AI's findings regarding the lifetime mismatch and teardown
  race condition:
  - Revert the driver from using devm allocations and managed hwmon
    registration.
  - Manually register with unmanaged hwmon_device_register_with_info()
    and manually free structures via applesmc_free_hwmon().
  - Ensure unregistration order is safe: call hwmon_device_unregister()
    at the very beginning of applesmc_exit() to close the sysfs nodes
    prior to freeing the register structures and dynamic memory.

Changes in v4:
- Convert to devres-managed devm_hwmon_device_register_with_info() to fix
  a lifetime Use-After-Free mismatch when the driver is unbound via sysfs
  (releasing devres-managed attributes memory while keeping the hwmon
  sysfs files active).
- Declare hwmon_dev locally in applesmc_init() and remove it from the
  global static variables, and clean up the redundant manual
  hwmon_device_unregister() call in applesmc_exit().

Changes in v3:
- Fix a recursive mutex deadlock in applesmc_hwmon_write() when writing
  to pwmX_enable by using applesmc_get_entry_by_key() to resolve the entry
  locklessly and then calling the underlying raw SMC read/write calls.
- Fix a fallback fan label truncation bug by pre-padding the generated fallback
  string with four spaces so that the "+ 4" pointer arithmetic offset yields the
  correct label "Fan %d".

Changes in v2:
- Abandon the minimal dummy registration approach in v1.
- Fully convert the driver to modern HWMON ABI standards by dynamically
  allocating temp and fan channels at initialization.
- Rename legacy non-standard attributes to comply with the standard HWMON ABI:
  - fanX_output -> fanX_target (HWMON_F_TARGET)
  - fanX_manual -> pwmX_enable (HWMON_PWM_ENABLE)
- Dynamically register the remaining non-standard fanX_safe attributes
  under HWMON class directory via extra_groups.
- Load and cache fan positions in smcreg.fan_positions to support returning
  labels by reference in .read_string.
- Clean up unused static attribute groups and show/store callback functions
  to avoid unused symbol compiler warnings.
- Verified compilation and successfully tested on real MacBook hardware.

We appreciate your review and comments on this refactoring.


Shih-Yuan Lee (3):
  hwmon: (applesmc) Cache fan positions during register initialization
  hwmon: (applesmc) Fix lockless cache validation data race
  hwmon: (applesmc) Convert to hwmon_device_register_with_info

 drivers/hwmon/applesmc.c | 490 +++++++++++++++++++++++++++------------
 1 file changed, 338 insertions(+), 152 deletions(-)

-- 
2.39.5