Messages in this thread Patch in this message | | | From | Allen Yu <> | Date | Mon, 16 Jun 2014 11:03:02 +0800 | Subject | RE: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended. |
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On Sat, 14 Jun 2014, Alan Stern wrote:
> > dev->power.is_suspended is set after core suspends device during system > suspend. > > This flag mostly means device is not operational (all I/O been > > quiesced, no more data read or write acceptible, etc.), hence it's > > dangerous to access hardware if device is suspended even though runtime > PM status is RPM_ACTIVE. > > > > In turn, we should allow device to be accessed in case device is *not* > > suspended and runtime PM status is RPM_ACTIVE, even if runtime PM > > disabled. This corner case can happen to a device in a generic PM > > domain if the domain is not powered off while preparing for a system-wide > power transition. > > I don't understand. Even if the PM domain isn't powered off, the device's > is_suspended flag will still be set by __device_suspend().
Yes, is_suspended flag will be set by __device_suspend(). But runtime PM can be disabled in pm_genpd_prepare():
914 static int pm_genpd_prepare(struct device *dev){ ... 956 /* 957 * The PM domain must be in the GPD_STATE_ACTIVE state at this point, 958 * so pm_genpd_poweron() will return immediately, but if the device 959 * is suspended (e.g. it's been stopped by genpd_stop_dev()), we need 960 * to make it operational. 961 */ 962 pm_runtime_resume(dev); 963 __pm_runtime_disable(dev, false); ... 978 }
And there is a gap between pm_genpd_prepare() and __device_suspend(), during which is_suspended flag is *not* yet set but runtime PM is disabled and device status is RPM_ACTIVE.
> > > In this case, runtime PM status will > > be set to RPM_ACTIVE and then runtime PM is disabled. After that, > > device driver may call pm_runtime_get_sync() and rpm_resume() should > > return 1, because the device is still active as long as not been suspended. > > Isn't that what the existing code does already? Your patch seems to change > it so that it _doesn't_ behave the way you want. >
The existing code return 1 for case is_suspended flag is set. That means __device_suspend() has been called and device is not in operational state. Whereas the case I mentioned above is before device is suspended. It's dangerous to access device if it's in suspended state, so I propose only allowing access to a device if it's not suspended (i.e. value of "is_suspneded" flag is false).
> > Signed-off-by: Allen Yu <alleny@nvidia.com> > > --- > > drivers/base/power/runtime.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/base/power/runtime.c > > b/drivers/base/power/runtime.c index 67c7938..39885f1 100644 > > --- a/drivers/base/power/runtime.c > > +++ b/drivers/base/power/runtime.c > > @@ -608,7 +608,7 @@ static int rpm_resume(struct device *dev, int > rpmflags) > > repeat: > > if (dev->power.runtime_error) > > retval = -EINVAL; > > - else if (dev->power.disable_depth == 1 && dev- > >power.is_suspended > > + else if (dev->power.disable_depth == 1 && !dev- > >power.is_suspended > > && dev->power.runtime_status == RPM_ACTIVE) > > retval = 1; > > Alan Stern
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