On pią, 2014-11-07 at 13:13 +0100, Pavel Machek wrote:

On Wed 2014-11-05 09:42:58, Krzysztof Kozlowski wrote:

quoted

On wto, 2014-11-04 at 21:18 +0100, Pavel Machek wrote:

quoted

On Tue 2014-11-04 13:52:48, Krzysztof Kozlowski wrote:

quoted

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 only disable/enable the clock in runtime suspend and
resume callbacks.

quoted

 /*
  * Hooks to provide runtime PM of the pclk (bus clock).  It is safe to
  * enable/disable the bus clock at runtime PM suspend/resume as this

@@ -95,8 +102,14 @@ 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) {
+		pcdev->irq_safe = get_pm_runtime_irq_safe(dev);
+
+		if (pcdev->irq_safe)
+			clk_disable(pcdev->pclk);
+		else
+			clk_disable_unprepare(pcdev->pclk);
+	}

So you can handle the case of !pcdev->irq_safe. What is the penalty
for always assuming !pcdev->irq_safe?

The penalty (for pl330 driver) would be that the runtime resume/suspend
cannot happen from atomic context
  => pm_runtime_get_sync() cannot be called from atomic context
    => complete rework of runtime PM for pl330 DMA driver because now
       one of pm_runtime_get_sync() calls is in device_issue_pending
       callback which may not sleep. And by "rework" I also mean that
       I do not know how to do this... yet.

I still don't get it. You say that you don't know how to handle
!pcdev->irq_safe case... Yet have code above that tries to handle it.

If that case can't be sanely handled, I'd expect
BUG_ON(!pcdev->irq_safe).

Hmmm... I could misunderstand your question. The amba/bus.c driver can
handle both cases. However this varies for child drivers (which use
these runtime PM callbacks too). For pl330 cannot handle non-irq-safe.
Other drivers can.

Is it the answer for your question?

Best regards,
Krzysztof