Re: [PATCH ver. 2] PM: add synchronous runtime interface for interrupt handlers

[Kevin Hilman <khilman@deeprootsystems.com>]

"Rafael J. Wysocki" <rjw@sisk.pl> writes:

> On Tuesday, November 23, 2010, Alan Stern wrote:
>> On Tue, 23 Nov 2010, Rafael J. Wysocki wrote:
>> 
>> > > > Moreover, I'm not sure if we need an "IRQ safe" version of _idle.  Why do
>> > > > we need it, exactly?
>> > > 
>> > > Because pm_runtime_put_sync() calls rpm_idle().  If there were no 
>> > > irq-safe version of rpm_idle() then drivers wouldn't be able to call 
>> > > pm_runtime_put_sync() from within an interrupt handler.
>> > 
>> > Right.  Which they can't do now, can they?
>> 
>> True.  That was the point of this patch -- to allow interrupt handlers
>> to do runtime PM, which they can't do now.
>
> The original idea was to allow suspend and resume to be carried out
> with interrupts off, not necessarily by interrupt handlers.  We've never
> considered doing that with _idle before.
>
>> > Why do you think we should allow them to do that?
>> 
>> Are you suggesting that interrupt handlers stick to pm_runtime_suspend 
>> and pm_runtime_resume, and ignore pm_runtime_get_sync and 
>> pm_runtime_put_sync?
>
> Why do they need the _sync versions?  What exactly is wrong with
> calling
>
> pm_runtime_put_noidle()
> pm_runtime_suspend()
>
> from an interrupt handler if it really wants the synchronous suspend to be
> carried out at this point?
>
> I don't really see a reason for calling pm_runtime_put_sync() by an interrupt
> handler, but perhaps I'm overlooking something important.

While I like the idea of the symmetry of having both _get_sync() and
_put_sync() callable from an interrupt handler, I can't currently think
of a situation where we would need to _put_sync() in the ISR.  A
standard _put() should suffice for all cases I can imagine.

Kevin