Alan Stern <st...@rowland.harvard.edu> writes:
> On Fri, 21 Sep 2012, Rafael J. Wysocki wrote:
>
>> > Kevin makes a good case that pm_runtime_resume() and related functions
>> > should succeed even when runtime PM is disabled, if the device is
>> > already in the desired state.
>> >
>> > The same may be true for pm_runtime_suspend(). What do you think?
>>
>> I've discussed that with Kevin. The problem is that the runtime PM
>> status may be changed at will when runtime PM is disabled by using
>> __pm_runtime_set_status(), so the status generally cannod be trusted
>> if power.disable_depth > 0.
>
> Hmmm. That same argument applies even when is_suspended is true.
> Runtime PM might have been disabled beforehand by the driver, so you
> still don't know whether to believe the status.
>
>> During system suspend, however, runtime PM is disabled by the core and
>> if neither the driver nor the subsystem has disabled it in the meantime,
>> the status should be actually valid.
>
> I suppose you could check that .disable_depth == 1. That would mean
> only the core had disabled runtime PM.
>
>> > The way the patch is written contradicts the documentation:
>> >
>> > * A request to execute ->runtime_resume() will cancel any pending or
>> > scheduled requests to execute the other callbacks for the same device,
>> > except for scheduled autosuspends.
>>
>> I'm not sure where the contradiction is. The patch simply changes the
>> behavior for disabled runtime PM, which is to return a nonzero value
>> immediately
>> anyway.
>
> It changes an error return to a non-error return.
>
> However, if we limit the effects to times when the system is
> suspending then there shouldn't be any pending or scheduled requests
> anyway. So okay, this isn't an issue.
>
>> > > > @@ -510,7 +510,8 @@ static int rpm_resume(struct device *dev, int
>> > > > rpmflags)
>> > > > if (dev->power.runtime_error)
>> > > > retval = -EINVAL;
>> > > > else if (dev->power.disable_depth > 0)
>> > > > - retval = -EACCES;
>> > > > + retval = dev->power.is_suspended &&
>> > > > + dev->power.runtime_status == RPM_ACTIVE ? 1 :
>> > > > -EACCES;
>> > > > if (retval)
>> > > > goto out;
>> >
>> > Also, the is_suspended test seems irrelevant in general -- it makes
>> > sense in terms of the scenario Kevin described but that's not the
>> > stated purpose of the patch.
>>
>> Well, it is, although the changelog doesn't state it sufficiently clearly.
>> :-)
>
> Good point. The changelog needs to be improved.
>
>> > Both of these problems can be addressed by writing the code as follows:
>> >
>> > if (dev->power.runtime_error)
>> > retval = -EINVAL;
>> > else if (dev->power.disable_depth > 0) {
>> >
>> > /* Special case: allow this if the device is already active */
>> > if (dev->power.runtime_status != RPM_ACTIVE)
>> > retval = -EACCES;
>> > }
>> > if (retval)
>> > goto out;
>>
>> We could do that too, but I'm a bit concerned about the situations where
>> runtime PM is disabled by the driver itself or by the subsystem, because
>> in those cases whoever disables runtime PM would have to make sure that the
>> status still reflects the actual hardware state, but that's what the runtime
>> PM framework is for (among other things).
>
> All right, let's use Kevin's original scheme but add a test for
> disable_depth == 1. I suggest changing the ?: operator to a regular
> "if" statement, because the new condition will be even longer than the
> old one (which I found a little hard to read in the first place).
>
> And of course, a comment should be added to explain the reason for the
> exception.
>
> Kevin, how does this sound?
>
Sounds good to me.
I'll respin and try to make the changelog more clear.
Thanks,
Kevin
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