Re: [PATCH v8 3/5] amba: Don't unprepare the clocks if device driver wants IRQ safe runtime PM

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Sat, Nov 01, 2014 at 12:55:14AM +0000, Russell King - ARM Linux wrote:
> On Sat, Nov 01, 2014 at 01:45:47AM +0100, Rafael J. Wysocki wrote:
> > On Monday, October 20, 2014 11:04:46 AM Krzysztof Kozlowski wrote:
> > > @@ -198,8 +217,10 @@ static int amba_probe(struct device *dev)
> > >  		pm_runtime_enable(dev);
> > >  
> > >  		ret = pcdrv->probe(pcdev, id);
> > > -		if (ret == 0)
> > > +		if (ret == 0) {
> > > +			pcdev->irq_safe = pm_runtime_is_irq_safe(dev);
> > 
> > This looks racy.
> > 
> > Is it guaranteed that runtime PM callbacks won't be run for the device
> > after pcdrv->probe() has returned and before setting pcdev->irq_safe?
> > If not, inconsistent behavior may ensue.
> 
> You are absolutely correct.  So that knocks that idea on its head.

Actually, I think we shouldn't give up hope here.  Currently, we do this:

                pm_runtime_get_noresume(dev);
                pm_runtime_set_active(dev);
                pm_runtime_enable(dev);

                ret = pcdrv->probe(pcdev, id);

What we could do is:

		pm_runtime_get_noresume(dev);
                pm_runtime_get_noresume(dev);
                pm_runtime_set_active(dev);
                pm_runtime_enable(dev);

                ret = pcdrv->probe(pcdev, id);
		if (ret == 0) {
			pcdev->irq_safe = pm_runtime_is_irq_safe(dev);
			pm_runtime_put(dev);
			break;
		}

                pm_runtime_disable(dev);
                pm_runtime_set_suspended(dev);
                pm_runtime_put_noidle(dev);
                pm_runtime_put_noidle(dev);

which would ensure that we hold a usecount until after the probe function
has returned.  Would that work?

I'll give you that it's pretty horrid.

Would another possible solution be to remember the irq-safeness in the
suspend handler, and use that in the resume handler?  Resume should
/always/ undo what the suspend handler previously did wrt clk API stuff.

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