Re: [PATCH v7 1/5] PM / Runtime: Add getter for quering the IRQ safe option
From: Russell King - ARM Linux
Date: Wed Sep 24 2014 - 15:52:46 EST
On Wed, Sep 24, 2014 at 03:47:17PM -0400, Alan Stern wrote:
> On Wed, 24 Sep 2014, Pavel Machek wrote:
> > On Wed 2014-09-24 15:50:08, Krzysztof Kozlowski wrote:
> > > Add a simple getter pm_runtime_is_irq_safe() for quering whether runtime
> > > PM IRQ safe was set or not.
> > >
> > > Various bus drivers implementing runtime PM may use choose to suspend
> > > differently based on IRQ safeness status of child driver (e.g. do not
> > > unprepare the clock if IRQ safe is not set).
> > >
> > > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>
> > > Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> > Are you sure this is good interface?
> > "Tell me if another function works this or that way".
> > That's certainly not traditional interface, and it seems dangerous to
> > me. Callbacks now have different semantic requirements based on value
> > of some flag...
> > Would it be possible to have two sets of callbacks, one irq safe and
> > one not?
> Or maybe add a flag to the bus-specific device structures, indicating
> specifically whether or not the clock should be unprepared during a
> runtime suspend. Then individual drivers could set this flag or not,
> independent of the irq-safe setting.
What you're proposing is _less_ safe, because with your proposal, you
now have the possibility that drivers will tell runtime PM that it has
IRQ safe callbacks, but the bus code tries to prepare/unprepare the
clock, which causes a might-sleep-if warning.
This is fragile.
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