[PATCH v4 3/4] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

[Krzysztof Kozlowski]

The AMBA bus driver defines runtime Power Management functions which
disable and unprepare AMBA bus clock. This is problematic for runtime PM
because unpreparing a clock might sleep so it is not interrupt safe.

However some drivers may want to implement runtime PM functions in
interrupt-safe way (see pm_runtime_irq_safe()). In such case the AMBA
bus driver should not unprepare/prepare the clock in runtime suspend and
resume callbacks.

Detect the device driver behavior after calling its probe function and
store it. During runtime suspend/resume deal with clocks according to
stored value.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>
---
 drivers/amba/bus.c       | 30 ++++++++++++++++++++++++++----
 include/linux/amba/bus.h |  1 +
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index 3cf61a127ee5..4aee6e61bed2 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -94,8 +94,18 @@ static int amba_pm_runtime_suspend(struct device *dev)
 	struct amba_device *pcdev = to_amba_device(dev);
 	int ret = pm_generic_runtime_suspend(dev);
 
-	if (ret == 0 && dev->driver)
-		clk_disable_unprepare(pcdev->pclk);
+	if (ret == 0 && dev->driver) {
+		/*
+		 * Drivers should not change pm_runtime_irq_safe()
+		 * after probe.
+		 */
+		WARN_ON(pcdev->irq_safe != pm_runtime_is_irq_safe(dev));
+
+		if (pcdev->irq_safe)
+			clk_disable(pcdev->pclk);
+		else
+			clk_disable_unprepare(pcdev->pclk);
+	}
 
 	return ret;
 }
@@ -106,7 +116,16 @@ static int amba_pm_runtime_resume(struct device *dev)
 	int ret;
 
 	if (dev->driver) {
-		ret = clk_prepare_enable(pcdev->pclk);
+		/*
+		 * Drivers should not change pm_runtime_irq_safe()
+		 * after probe.
+		 */
+		WARN_ON(pcdev->irq_safe != pm_runtime_is_irq_safe(dev));
+
+		if (pcdev->irq_safe)
+			ret = clk_enable(pcdev->pclk);
+		else
+			ret = clk_prepare_enable(pcdev->pclk);
 		/* Failure is probably fatal to the system, but... */
 		if (ret)
 			return ret;
@@ -191,8 +210,11 @@ static int amba_probe(struct device *dev)
 		pm_runtime_enable(dev);
 
 		ret = pcdrv->probe(pcdev, id);
-		if (ret == 0)
+		if (ret == 0) {
+			if (pm_runtime_is_irq_safe(dev))
+				pcdev->irq_safe = 1;
 			break;
+		}
 
 		pm_runtime_disable(dev);
 		pm_runtime_set_suspended(dev);
diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
index ad52027a9cbf..ce101e4497d6 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -32,6 +32,7 @@ struct amba_device {
 	struct clk		*pclk;
 	unsigned int		periphid;
 	unsigned int		irq[AMBA_NR_IRQS];
+	unsigned int		irq_safe:1;
 };
 
 struct amba_driver {
-- 
1.9.1

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