1 files changed, 46 insertions, 29 deletions

diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index fb142dfbb237..237d7d5cc8a8 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -750,6 +750,8 @@ int rpmh_rsc_write_ctrl_data(struct rsc_drv *drv, const struct tcs_request *msg)
  * SLEEP and WAKE sets. If AMCs are busy, controller can not enter
  * power collapse, so deny from the last cpu's pm notification.
  *
+ * Context: Must be called with the drv->lock held.
+ *
  * Return:
  * * False		- AMCs are idle
  * * True		- AMCs are busy
@@ -764,9 +766,6 @@ static bool rpmh_rsc_ctrlr_is_busy(struct rsc_drv *drv)
 	 * dedicated TCS for active state use, then re-purposed wake TCSes
 	 * should be checked for not busy, because we used wake TCSes for
 	 * active requests in this case.
-	 *
-	 * Since this is called from the last cpu, need not take drv->lock
-	 * before checking tcs_is_free().
 	 */
 	if (!tcs->num_tcs)
 		tcs = &drv->tcs[WAKE_TCS];
@@ -801,43 +800,62 @@ static int rpmh_rsc_cpu_pm_callback(struct notifier_block *nfb,
 {
 	struct rsc_drv *drv = container_of(nfb, struct rsc_drv, rsc_pm);
 	int ret = NOTIFY_OK;
-
-	spin_lock(&drv->pm_lock);
+	int cpus_in_pm;
 
 	switch (action) {
 	case CPU_PM_ENTER:
-		cpumask_set_cpu(smp_processor_id(), &drv->cpus_entered_pm);
-
-		if (!cpumask_equal(&drv->cpus_entered_pm, cpu_online_mask))
-			goto exit;
+		cpus_in_pm = atomic_inc_return(&drv->cpus_in_pm);
+		/*
+		 * NOTE: comments for num_online_cpus() point out that it's
+		 * only a snapshot so we need to be careful. It should be OK
+		 * for us to use, though.  It's important for us not to miss
+		 * if we're the last CPU going down so it would only be a
+		 * problem if a CPU went offline right after we did the check
+		 * AND that CPU was not idle AND that CPU was the last non-idle
+		 * CPU. That can't happen. CPUs would have to come out of idle
+		 * before the CPU could go offline.
+		 */
+		if (cpus_in_pm < num_online_cpus())
+			return NOTIFY_OK;
 		break;
 	case CPU_PM_ENTER_FAILED:
 	case CPU_PM_EXIT:
-		cpumask_clear_cpu(smp_processor_id(), &drv->cpus_entered_pm);
-		goto exit;
+		atomic_dec(&drv->cpus_in_pm);
+		return NOTIFY_OK;
 	default:
-		ret = NOTIFY_DONE;
-		goto exit;
+		return NOTIFY_DONE;
 	}
 
-	ret = rpmh_rsc_ctrlr_is_busy(drv);
-	if (ret) {
-		ret = NOTIFY_BAD;
-		goto exit;
+	/*
+	 * It's likely we're on the last CPU. Grab the drv->lock and write
+	 * out the sleep/wake commands to RPMH hardware. Grabbing the lock
+	 * means that if we race with another CPU coming up we are still
+	 * guaranteed to be safe. If another CPU came up just after we checked
+	 * and has grabbed the lock or started an active transfer then we'll
+	 * notice we're busy and abort. If another CPU comes up after we start
+	 * flushing it will be blocked from starting an active transfer until
+	 * we're done flushing. If another CPU starts an active transfer after
+	 * we release the lock we're still OK because we're no longer the last
+	 * CPU.
+	 */
+	if (spin_trylock(&drv->lock)) {
+		if (rpmh_rsc_ctrlr_is_busy(drv) || rpmh_flush(&drv->client))
+			ret = NOTIFY_BAD;
+		spin_unlock(&drv->lock);
+	} else {
+		/* Another CPU must be up */
+		return NOTIFY_OK;
 	}
 
-	ret = rpmh_flush(&drv->client);
-	if (ret)
-		ret = NOTIFY_BAD;
-	else
-		ret = NOTIFY_OK;
-
-exit:
-	if (ret == NOTIFY_BAD)
-		/* We won't be called w/ CPU_PM_ENTER_FAILED */
-		cpumask_clear_cpu(smp_processor_id(), &drv->cpus_entered_pm);
+	if (ret == NOTIFY_BAD) {
+		/* Double-check if we're here because someone else is up */
+		if (cpus_in_pm < num_online_cpus())
+			ret = NOTIFY_OK;
+		else
+			/* We won't be called w/ CPU_PM_ENTER_FAILED */
+			atomic_dec(&drv->cpus_in_pm);
+	}
 
-	spin_unlock(&drv->pm_lock);
 	return ret;
 }
 
@@ -980,7 +998,6 @@ static int rpmh_rsc_probe(struct platform_device *pdev)
 	solver_config = solver_config >> DRV_HW_SOLVER_SHIFT;
 	if (!solver_config) {
 		drv->rsc_pm.notifier_call = rpmh_rsc_cpu_pm_callback;
-		spin_lock_init(&drv->pm_lock);
 		cpu_pm_register_notifier(&drv->rsc_pm);
 	}