[PATCH v2 2/2] PM: clk: Release the clock prepare reference across runtime suspend

[Loic Poulain <loic.poulain@oss.qualcomm.com>]

The PM clock layer prepares a clock at acquire time and keeps that
reference until the entry is removed, pm_clk_suspend() only dropping
the enable reference. A prepare reference propagates to the parents
though, so a clock with enable/disable ops can keep an ancestor that
only implements prepare/unprepare running for as long as the device
exists. On Qualcomm platforms this keeps the RPM XO clock active
across runtime and system suspend even though all of its consumers
are suspended.

Unprepare on suspend for devices that are not IRQ-safe, as those
suspend in process context, and let the next pm_clk_resume() prepare
the clock again. This generalises the clk_is_enabled_when_prepared()
check in pm_clk_acquire(), which only considers the clock itself and
not its parents. Most drivers managing their own clocks already
unprepare in runtime suspend: 245 call sites under drivers/ against
27 that only disable.

Reported-by: Nihal Kumar Gupta <nihal.gupta@oss.qualcomm.com>
Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
---
 drivers/base/power/clock_ops.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/base/power/clock_ops.c b/drivers/base/power/clock_ops.c
index 6f66e11a12428fb718abca197f5519b1ee21ff90..43150ecb58add7783d8602d525219c676fd808fe 100644
--- a/drivers/base/power/clock_ops.c
+++ b/drivers/base/power/clock_ops.c
@@ -33,7 +33,6 @@ struct pm_clock_entry {
 	char *con_id;
 	struct clk *clk;
 	enum pce_status status;
-	bool enabled_when_prepared;
 };
 
 /**
@@ -174,9 +173,11 @@ static void pm_clk_acquire(struct device *dev, struct pm_clock_entry *ce)
 		ce->status = PCE_STATUS_ERROR;
 		return;
 	} else if (clk_is_enabled_when_prepared(ce->clk)) {
-		/* we defer preparing the clock in that case */
+		/*
+		 * Preparing the clock would also start it, so defer that to
+		 * the first pm_clk_resume().
+		 */
 		ce->status = PCE_STATUS_ACQUIRED;
-		ce->enabled_when_prepared = true;
 	} else if (clk_prepare(ce->clk)) {
 		ce->status = PCE_STATUS_ERROR;
 		dev_err(dev, "clk_prepare() failed\n");
@@ -460,6 +461,7 @@ EXPORT_SYMBOL_GPL(devm_pm_clk_create);
 int pm_clk_suspend(struct device *dev)
 {
 	struct pm_subsys_data *psd = dev_to_psd(dev);
+	bool sleepable = !pm_runtime_is_irq_safe(dev);
 	struct pm_clock_entry *ce;
 	unsigned long flags;
 
@@ -472,7 +474,7 @@ int pm_clk_suspend(struct device *dev)
 
 	list_for_each_entry_reverse(ce, &psd->clock_list, node) {
 		if (ce->status == PCE_STATUS_ENABLED) {
-			if (ce->enabled_when_prepared) {
+			if (sleepable) {
 				clk_disable_unprepare(ce->clk);
 				ce->status = PCE_STATUS_ACQUIRED;
 			} else {

-- 
2.34.1