Re: [PATCH v9 2/4] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

[Krzysztof Kozlowski <k.kozlowski@samsung.com>]

On wto, 2014-11-04 at 20:06 +0100, Ulf Hansson wrote:
> On 4 November 2014 13:52, Krzysztof Kozlowski <k.kozlowski@samsung.com> 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.
> >
> > Detect the device driver behavior during runtime suspend. During runtime
> > resume deal with clocks according to stored value.
> >
> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
> > ---
> >  drivers/amba/bus.c       | 24 ++++++++++++++++++++----
> >  include/linux/amba/bus.h |  1 +
> >  2 files changed, 21 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> > index 47bbdc1b5be3..27ec8882ec8e 100644
> > --- a/drivers/amba/bus.c
> > +++ b/drivers/amba/bus.c
> > @@ -85,6 +85,13 @@ static struct device_attribute amba_dev_attrs[] = {
> >  };
> >
> >  #ifdef CONFIG_PM
> > +
> > +#ifdef CONFIG_PM_RUNTIME
> > +#define get_pm_runtime_irq_safe(dev)   ((dev)->power.irq_safe)
> > +#else
> > +#define get_pm_runtime_irq_safe(dev)   1
> 
> No, this doesn't work for those drivers that isn't configured as
> irq_safe. The pm_runtime_force_suspend() invoked from the driver's
> system PM suspend callback, will expect clocks to be unprepared when
> CONFIG_PM_RUNTIME is unset.

D'oh! You're right... 

> To address this issue, in principle we need to know whether the driver
> has invoked pm_runtime_irq_safe(), even when CONFIG_PM_RUNTIME is
> unset.
> 
> This may be solved by the help of PM core:
> 1) Move the irq_safe member in the struct dev_pm_info, outside the
> #ifdef CONFIG_PM_RUNTIME.
> 2) Let the pm_runtime_irq_safe() function be implemented for CONFIG_PM
> instead of CONFIG_PM_RUNTIME.

Before I'll start implementing this - could PM maintainers share their
opinion on such change?

Best regards,
Krzysztof


> If the PM core maintainers don't like that approach we can always add
> an amba specific wrapper function for pm_runtime_irq_safe() and store
> the information needed in the struct amba_device.
> 
> Kind regards
> Uffe