[PATCH v2 0/6] watchdog: starfive: runtime PM cleanup

[William Theesfeld]

The v1 patch was a one-line conversion of pm_runtime_get_sync() to
pm_runtime_resume_and_get() in starfive_wdt_pm_start().  On review,
the StarFive maintainers pointed out one edge case the v1 fix had
missed, plus five pre-existing issues in the surrounding runtime PM
handling that all need to be addressed before the original fix is
useful in practice.

This v2 turns the single fix into a six-patch series.  Each patch
addresses one independent issue and can be reviewed in isolation;
they are ordered roughly from the simplest correctness fix to the
ones requiring a small amount of restructuring.

The series:

  1/6  Expand the original v1 fix so the runtime PM reference is also
       released when starfive_wdt_start() fails after a successful
       pm_runtime_resume_and_get().

  2/6  Treat a return value of 1 from pm_runtime_put_sync() as success
       in both starfive_wdt_pm_stop() and the probe path; the watchdog
       framework currently propagates the value verbatim and the probe
       takes the err_unregister_wdt path on a non-error return.

  3/6  Restructure starfive_wdt_probe() error handling into three
       labels (err_pm_disable / err_put_pm / err_unregister_wdt) so
       every failure path balances exactly the resources it has
       acquired.  Previously two early failure paths returned without
       calling pm_runtime_disable() and several later paths leaked the
       runtime PM reference.

  4/6  Gate the system suspend / resume callbacks with
       pm_runtime_status_suspended() so the WDOGLOAD / WDOGCONTROL
       accesses run only when the device is actually clocked.  When
       the device was already runtime-suspended the previous code
       triggered a synchronous external abort.

  5/6  Make starfive_wdt_shutdown() only drop the PM refcount when
       WDOG_ACTIVE is set, and stop just the hardware (no PM touch)
       when only WDOG_HW_RUNNING is set.  This avoids the refcount
       underflow that the previous unconditional pm_stop() produced.

  6/6  Release the early_enable PM refcount in starfive_wdt_remove()
       when WDOG_HW_RUNNING is still asserted at unregister time.  The
       watchdog framework's stop-on-unregister path only runs the
       stop op when WDOG_ACTIVE is set, so the early-enable +
       never-opened combination otherwise leaks the probe-time
       reference.

The whole series builds cleanly with CONFIG_STARFIVE_WATCHDOG=m on
x86_64 defconfig.  Runtime testing would require StarFive JH7100 /
JH7110 hardware and has not been performed.

William Theesfeld (6):
  watchdog: starfive: balance PM refcount when start operation fails
  watchdog: starfive: treat pm_runtime_put_sync() positive return as
    success
  watchdog: starfive: balance PM refcount and disable in probe error
    paths
  watchdog: starfive: guard system suspend/resume hardware access
  watchdog: starfive: avoid PM refcount underflow in shutdown
  watchdog: starfive: release early_enable PM refcount on remove

 drivers/watchdog/starfive-wdt.c | 92 ++++++++++++++++++++++++++-------
 1 file changed, 73 insertions(+), 19 deletions(-)

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2.54.0