[PATCH v4 2/6] PM: runtime: Add pm_runtime_if_active guard and conditional variant

[Rafael J. Wysocki (Intel)]

On Fri, Oct 9, 2026 at 6:00 AM Golla Nagendra <nagendra.golla at amd.com> wrote:
>
> Add a pm_runtime_if_active base guard and its _try conditional variant
> to pm_runtime.h for drivers that need to conditionally acquire a runtime
> PM reference only when the device is already active.
>
> The base guard must not be used directly via guard()/scoped_guard()
> because pm_runtime_get_if_active() only acquires a reference when it
> returns 1; the destructor unconditionally calls pm_runtime_put(), which
> would underflow usage_count on a suspended device. The base guard
> exists solely to back the DEFINE_GUARD_COND _try variant.
>
> The _try variant (used via PM_RUNTIME_ACQUIRE_IF_ACTIVE) satisfies the
> _try API contract that guards must not produce an error when runtime PM
> is disabled for the device. When pm_runtime_get_if_active() returns
> -EINVAL (runtime PM disabled), the expression calls
> pm_runtime_get_noresume() to pre-balance the destructor's unconditional
> pm_runtime_put(), then returns 1 so the guard condition succeeds
> (bypass). This mirrors the behaviour of pm_runtime_active_try which
> uses RPM_TRANSPARENT for the same purpose. When the device is genuinely
> runtime-suspended (return value 0), the guard condition fails and
> ACQUIRE_ERR returns true, allowing callers such as interrupt handlers to
> skip MMIO accesses.
>
> Signed-off-by: Golla Nagendra <nagendra.golla at amd.com>
> ---
>  include/linux/pm_runtime.h | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index 64921b10ac74..ae2a8740ffb3 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -609,6 +609,13 @@ DEFINE_GUARD(pm_runtime_active, struct device *,
>              pm_runtime_get_sync(_T), pm_runtime_put(_T));
>  DEFINE_GUARD(pm_runtime_active_auto, struct device *,
>              pm_runtime_get_sync(_T), pm_runtime_put_autosuspend(_T));
> +/*
> + * Do not use directly -- the destructor calls pm_runtime_put()
> + * unconditionally, which underflows if no reference was acquired.
> + * Use only via the _try variant below.
> + */
> +DEFINE_GUARD(pm_runtime_if_active, struct device *,
> +            pm_runtime_get_if_active(_T), pm_runtime_put(_T));
>  /*
>   * Use the following guards with ACQUIRE()/ACQUIRE_ERR().
>   *
> @@ -624,6 +631,23 @@ DEFINE_GUARD_COND(pm_runtime_active_auto, _try,
>                   pm_runtime_get_active(_T, RPM_TRANSPARENT), _RET == 0)
>  DEFINE_GUARD_COND(pm_runtime_active_auto, _try_enabled,
>                   pm_runtime_resume_and_get(_T), _RET == 0)
> +/*
> + * The _try contract is that no error is produced when runtime PM is disabled,
> + * so bypass the guard when pm_runtime_get_if_active() returns -EINVAL: take a
> + * reference with pm_runtime_get_noresume() to pre-balance the destructor's
> + * pm_runtime_put() and return 1 so the guard condition succeeds. Interrupt
> + * handlers then keep servicing interrupts when runtime PM is disabled for the
> + * device or CONFIG_PM is not enabled.
> + */
> +DEFINE_GUARD_COND(pm_runtime_if_active, _try,
> +                 ({
> +                       int _r = pm_runtime_get_if_active(_T);
> +
> +                       if (_r == -EINVAL)
> +                               pm_runtime_get_noresume(_T);
> +                       _r == -EINVAL ? 1 : (_r ?: -EAGAIN);
> +                 }),
> +                 _RET == 1)
>
>  /* ACQUIRE() wrapper macros for the guards defined above. */
>
> @@ -639,6 +663,9 @@ DEFINE_GUARD_COND(pm_runtime_active_auto, _try_enabled,
>  #define PM_RUNTIME_ACQUIRE_IF_ENABLED_AUTOSUSPEND(_dev, _var)  \
>         ACQUIRE(pm_runtime_active_auto_try_enabled, _var)(_dev)
>
> +#define PM_RUNTIME_ACQUIRE_IF_ACTIVE(_dev, _var)       \
> +       ACQUIRE(pm_runtime_if_active_try, _var)(_dev)
> +
>  /*
>   * ACQUIRE_ERR() wrapper macro for guard pm_runtime_active.
>   *
>
> --

For the record, I'm still unconvinced about the guard definitions above.

Please try to reimplement the series without them for the time being.

Thanks!