[Intel-gfx] [PATCH v2] PM / Runtime: Introduce pm_runtime_get_noidle

[Rafael J. Wysocki]

On Friday, December 11, 2015 01:03:50 PM Ulf Hansson wrote:
> [...]
> 
> >> >
> >> > Which basically means you can call pm_runtime_resume() just fine,
> >> > because it will do nothing if the status is RPM_ACTIVE already.
> >> >
> >> > So really, why don't you use pm_runtime_get_sync()?
> >>
> >> The difference would be that if the status is not RPM_ACTIVE already we
> >> would drop the reference and report error. The caller would in this
> >> case forego of doing something, since we the device is suspended or on
> >> the way to being suspended. One example of such a scenario is a
> >> watchdog like functionality: the watchdog work would
> >> call pm_runtime_get_noidle() and check if the device is ok by doing
> >> some HW access, but only if the device is powered. Otherwise the work
> >> item would do nothing (meaning it also won't reschedule itself). The
> >> watchdog work would get rescheduled next time the device is woken up
> >> and some work is submitted to the device.
> >
> > So first of all the name "pm_runtime_get_noidle" doesn't make sense.
> >
> > I guess what you need is something like
> >
> > bool pm_runtime_get_if_active(struct device *dev)
> > {
> >         unsigned log flags;
> >         bool ret;
> >
> >         spin_lock_irqsave(&dev->power.lock, flags);
> >
> >         if (dev->power.runtime_status == RPM_ACTIVE) {
> >                 atomic_inc(&dev->power.usage_count);
> >                 ret = true;
> >         } else {
> >                 ret = false;
> >         }
> >
> >         spin_unlock_irqrestore(&dev->power.lock, flags);
> > }
> >
> > and the caller will simply bail out if "false" is returned, but if "true"
> > is returned, it will have to drop the usage count, right?
> >
> > Thanks,
> > Rafael
> >
> 
> Why not just:
> 
> pm_runtime_get_noresume():
> if (RPM_ACTIVE)
>   "do some actions"
> pm_runtime_put();

Because that's racy?

What if the rpm_suspend() is running for the device, but it hasn't changed
the status yet?

Thanks,
Rafael