[PATCH v4 2/4] PM / QoS: add lockless read for flags

Add a lockless read for QoS flags similar to the lockless read for
resume latency (dev_pm_qos_raw_resume_latency) which may be called
from atomic context (e.g. genpd governors running under a raw spinlock
or in the syscore suspend path), where taking that sleeping lock would
be invalid on PREEMPT_RT.

dev_pm_qos_raw_flags() now reads dev->power.qos->flags.effective_flags
with READ_ONCE() so also add corresponding WRITE_ONCE() to the two
effective_flags writes, the same way pm_qos_set_value() already does
for target_value/pm_qos_read_value().

Signed-off-by: Kevin Hilman (TI) <[email protected]>
---
 include/linux/pm_qos.h | 7 +++++++
 kernel/power/qos.c     | 4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
index aededda52b6b..439a9e779d81 100644
--- a/include/linux/pm_qos.h
+++ b/include/linux/pm_qos.h
@@ -219,6 +219,12 @@ static inline s32 dev_pm_qos_raw_resume_latency(struct device *dev)
 		PM_QOS_RESUME_LATENCY_NO_CONSTRAINT :
 		pm_qos_read_value(&dev->power.qos->resume_latency);
 }
+
+static inline s32 dev_pm_qos_raw_flags(struct device *dev)
+{
+	return IS_ERR_OR_NULL(dev->power.qos) ?
+		0 : READ_ONCE(dev->power.qos->flags.effective_flags);
+}
 #else
 static inline enum pm_qos_flags_status __dev_pm_qos_flags(struct device *dev,
 							  s32 mask)
@@ -300,6 +306,7 @@ static inline s32 dev_pm_qos_raw_resume_latency(struct device *dev)
 {
 	return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
 }
+static inline s32 dev_pm_qos_raw_flags(struct device *dev) { return 0; }
 #endif
 
 static inline int freq_qos_request_active(struct freq_qos_request *req)
diff --git a/kernel/power/qos.c b/kernel/power/qos.c
index 1944dbeb0d4c..c241da5bccf6 100644
--- a/kernel/power/qos.c
+++ b/kernel/power/qos.c
@@ -159,7 +159,7 @@ static void pm_qos_flags_remove_req(struct pm_qos_flags *pqf,
 	list_for_each_entry(req, &pqf->list, node)
 		val |= req->flags;
 
-	pqf->effective_flags = val;
+	WRITE_ONCE(pqf->effective_flags, val);
 }
 
 /**
@@ -193,7 +193,7 @@ bool pm_qos_update_flags(struct pm_qos_flags *pqf,
 		req->flags = val;
 		INIT_LIST_HEAD(&req->node);
 		list_add_tail(&req->node, &pqf->list);
-		pqf->effective_flags |= val;
+		WRITE_ONCE(pqf->effective_flags, pqf->effective_flags | val);
 		break;
 	default:
 		/* no action */

-- 
2.47.3