usb: dwc3: of-simple: fix use-after-free on remove

[Felipe Balbi <balbi@kernel.org>]

Hi,

Tony Lindgren <tony@atomide.com> writes:
> * Felipe Balbi <balbi@kernel.org> [180619 01:23]:
>> This is a direct consequence of not paying attention to the order of
>> things. If driver were to assume that pm_domain->activate() would do the
>> right thing for the device -- meaning that probe would run with an
>> active device --, then we wouldn't need that pm_runtime_get() call on
>> probe at all. Rather we would follow the sequence:
>> 
>> 	pm_runtime_forbid()
>> 	pm_runtime_set_active()
>> 	pm_runtime_enable()
>> 
>> 	/* do your probe routine */
>> 
>> 	pm_runtime_put_noidle()
>> 
>> Then you remove you would need to call pm_runtime_get_noresume() to
>> balance out the pm_runtime_put_noidle() there.
>
> How about let's create some prettier interface for the above runtime PM
> trickery?
>
> How about something like pm_runtime_init_enabled() for the above
> sequence?
>
> It might be then able to do the trick even if activate is not
> implemented..
>
> Right now it has the feeling of "oh well we can't get runtime PM to
> work so let's bypass it with activate call and then trick runtime PM
> to start in enabled mode" :)

no strong feelings about that either way. It's only 3 lines of code
anyway. I feel like that's a minor cosmetic change.

>> (If you need to know why the pm_runtime_put_noidle(), remember that
>> pm_runtime_set_active() increments the usage counter, so
>> pm_runtime_put_noidle is basically allowing pm_runtime to happen as soon
>> as userspace writes "auto" to /sys/..../power/control)
>
> I wonder if we could also remove the need for drivers to call
> pm_runtime_putnoidle() at the end of the probe? If we had
> pm_runtime_init_enabled() implemented.

probably not. We want to block runtime pm during probe, until the device
is fully initialized, the only way to do that is to increment rpm usage
counter.