On Thu, Sep 2, 2010 at 2:05 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > On Thursday, September 02, 2010, Colin Cross wrote: >> On Thu, Sep 2, 2010 at 12:46 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: >> > On Thursday, September 02, 2010, Alan Stern wrote: >> >> On Wed, 1 Sep 2010, Colin Cross wrote: >> >> >> >> > Only wait on a parent device during resume if the parent device is >> >> > suspended. >> >> > >> >> > Consider three drivers, A, B, and C. The parent of A is C, and C >> >> > has async_suspend set. On boot, C->power.completion is initialized >> >> > to 0. >> >> > >> >> > During the first suspend: >> >> > suspend_devices_and_enter(...) >> >> > dpm_resume(...) >> >> > device_suspend(A) >> >> > device_suspend(B) returns error, aborts suspend >> >> > dpm_resume_end(...) >> >> > dpm_resume(...) >> >> > device_resume(A) >> >> > dpm_wait(A->parent == C) >> >> > wait_for_completion(C->power.completion) >> >> > >> >> > The wait_for_completion will never complete, because >> >> > complete_all(C->power.completion) will only be called from >> >> > device_suspend(C) or device_resume(C), neither of which is called >> >> > if suspend is aborted before C. >> >> >> >> This would work okay if C->power.completion had been initialized to the >> >> completed state during boot, right? >> >> >> >> > After a successful suspend->resume cycle, where B doesn't abort >> >> > suspend, C->power.completion is left in the completed state by the >> >> > call to device_resume(C), and the same call path will work if B >> >> > aborts suspend. >> >> > >> >> > Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx> >> >> > --- >> >> > drivers/base/power/main.c | 3 ++- >> >> > 1 files changed, 2 insertions(+), 1 deletions(-) >> >> > >> >> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c >> >> > index cb784a0..e159910 100644 >> >> > --- a/drivers/base/power/main.c >> >> > +++ b/drivers/base/power/main.c >> >> > @@ -526,7 +526,8 @@ static int device_resume(struct device *dev, pm_message_t state, bool async) >> >> > TRACE_DEVICE(dev); >> >> > TRACE_RESUME(0); >> >> > >> >> > - dpm_wait(dev->parent, async); >> >> > + if (dev->parent && dev->parent->power.status >= DPM_OFF) >> >> > + dpm_wait(dev->parent, async); >> >> > device_lock(dev); >> >> > >> >> > dev->power.status = DPM_RESUMING; >> >> >> >> I think it would be better to change device_pm_init() and add a >> >> complete_all(). >> > >> > I agree. >> That would work, and was my first solution, but it increases the >> reliance on the completion variable being left completed between state >> transitions, which is undocumented and unnecessary. > > In fact it is necessary, because dpm_wait() may be called by external code > through device_pm_wait_for_dev() which is exported for a reason. That may > lead to problems analogous to the one you described if the completion > variables are not completed initially. > >> It seems more straightforward to me to only wait on the parent if the parent is >> suspended. >> >> > Who's writing the patch? >> I'll write it if you still don't like this one. > > Yes, please. OK - do you prefer it in dpm_prepare or device_pm_init? _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
