[PATCH 0/5] watchdog: starfive-wdt: Fix runtime PM and unclocked register access bugs

[Guenter Roeck <linux@roeck-us.net>]

The StarFive watchdog driver (drivers/watchdog/starfive-wdt.c) gates its
APB and core clocks via runtime PM callbacks, but has several runtime PM
reference-counting, ordering, and unclocked MMIO access bugs across
probe, remove, start/stop, shutdown, and system sleep paths:

1. In starfive_wdt_pm_start(), if starfive_wdt_start() fails after
   pm_runtime_resume_and_get() succeeds, the acquired runtime PM
   reference is leaked because the watchdog core does not call the stop
   callback when start fails.
2. In starfive_wdt_probe(), early returns on pm_runtime_resume_and_get()
   or starfive_wdt_enable_clock() failure bypass pm_runtime_disable(),
   leaving the runtime PM disable_depth counter unbalanced.
3. When runtime PM has suspended an idle watchdog and gated its clocks,
   starfive_wdt_remove(), starfive_wdt_shutdown(), starfive_wdt_suspend(),
   and starfive_wdt_resume() unconditionally read and write hardware
   registers, causing unclocked MMIO bus faults. In addition,
   starfive_wdt_pm_stop() propagates non-zero idle return codes from
   pm_runtime_put_sync() as errors to watchdog_stop().
4. Probe error paths after pm_runtime_resume_and_get() disable clocks
   manually without releasing the runtime PM reference (and without
   stopping an early_enable watchdog if registration fails), and
   starfive_wdt_remove() never drops the active runtime PM reference
   retained when watchdog_hw_running() is still set (e.g. early_enable).
5. In starfive_wdt_probe(), watchdog_register_device() is called before
   pm_runtime_put_sync() drops the probe-time reference, and non-zero
   idle return values such as -EAGAIN (triggered if userspace opens
   /dev/watchdog immediately upon registration) are treated as fatal
   probe errors.

These bugs have been reported by Sashiko.

This 5-patch series fixes each of these issues cleanly in sequence.

Note on tooling and testing:
This series was generated with an AI coding assistant (Jetski / Gemini)
following analysis of reported runtime PM and lifecycle bugs in
starfive-wdt.c. All patches were build-tested with make allmodconfig and
make W=1 with zero warnings, verified with scripts/checkpatch.pl
--strict, and validated against a state-machine simulation harness
covering runtime PM, clock gating, and concurrent open paths; they were
not tested on physical StarFive JH7100/JH7110 hardware.

Guenter Roeck (5):
  watchdog: starfive-wdt: Drop runtime PM reference if starting watchdog
    fails
  watchdog: starfive-wdt: Balance pm_runtime_enable() on probe error
    paths
  watchdog: starfive-wdt: Avoid unclocked register access in remove and
    PM paths
  watchdog: starfive-wdt: Fix runtime PM usage count leaks in probe and
    remove
  watchdog: starfive-wdt: Drop runtime PM reference before registering
    watchdog

 drivers/watchdog/starfive-wdt.c | 75 +++++++++++++++++++++------------
 1 file changed, 48 insertions(+), 27 deletions(-)

Cc: Xingyu Wu <xingyu.wu@starfivetech.com>
Cc: Ziv Xu <ziv.xu@starfivetech.com>
-- 
2.56.0