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

[Golla Nagendra]

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@xxxxxxx>
---
 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.
  *

-- 
2.43.7