On wto, 2014-11-04 at 21:18 +0100, Pavel Machek wrote:
> On Tue 2014-11-04 13:52:48, Krzysztof Kozlowski wrote:
> > 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.
>
>
>
> > /*
> > * 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.
Best regards,
Krzysztof
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