On Friday, July 01, 2011, Kevin Hilman wrote: > Continuing on the theme of runtime PM interactions with other parts of > the driver core... > > In drivers/base/dd.c:driver_probe_device(), the driver core increments > the usage count around ->probe(): > > [...] > pm_runtime_get_noresume(dev); > pm_runtime_barrier(dev); > ret = really_probe(dev, drv); > pm_runtime_put_sync(dev); > > I'm not following the reason for this. On driver's I'm familar with, > it's not until ->probe where pm_runtime_enable() is called. What is > being protected against here? > > These seem to exist since the introduction of the runtime PM core, but I > can't find any explanation. > > The documentation refers to the increment by the core, but not the > reasons why: > > If the device bus type's or driver's ->probe() or ->remove() > callback runs pm_runtime_suspend() or pm_runtime_idle() or their > asynchronous counterparts, they will fail returning -EAGAIN, because > the device's usage counter is incremented by the core before > executing ->probe() and ->remove(). Still, it may be desirable to > suspend the device as soon as ->probe() or ->remove() has finished, > so the PM core uses pm_runtime_idle_sync() to invoke the > subsystem-level idle callback for the device at that time. > > On a side note, the bit about -EAGAIN above is not accurate with today's > code. For example, __pm_runtime_suspend() returns zero when the usage > count decrement is non-zero, so callers can't currently know that doing > a pm_runtime_suspend() or pm_runtime_put_sync() in their ->probe() > actually didn't happen. > > Another curiosity is that, contrary to the above documentation, there is > no usage_count increment before the bus/driver ->remove() (although > there is a _get_sync/_put_sync around the sysfs_remove and notifier just > before the bus/driver->remove(). > > Also, below is a patch for a typo in the above Documentation exerpt. > > Kevin > > > > From 069484f8d2bb86473a271c27733e10fbfd410c2c Mon Sep 17 00:00:00 2001 > From: Kevin Hilman <khilman@xxxxxx> > Date: Thu, 30 Jun 2011 15:07:31 -0700 > Subject: [PATCH] PM: Documentation: fix typo: pm_runtime_idle_sync() doesn't exist. > > Replace reference to pm_runtime_idle_sync() in the driver core with > pm_runtime_put_sync() which is used in the code. > > Signed-off-by: Kevin Hilman <khilman@xxxxxx> Applied to suspend-2.6/linux-next. Thanks, Rafael > --- > Documentation/power/runtime_pm.txt | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt > index 22accb3..518d9be 100644 > --- a/Documentation/power/runtime_pm.txt > +++ b/Documentation/power/runtime_pm.txt > @@ -506,7 +506,7 @@ pm_runtime_suspend() or pm_runtime_idle() or their asynchronous counterparts, > they will fail returning -EAGAIN, because the device's usage counter is > incremented by the core before executing ->probe() and ->remove(). Still, it > may be desirable to suspend the device as soon as ->probe() or ->remove() has > -finished, so the PM core uses pm_runtime_idle_sync() to invoke the > +finished, so the PM core uses pm_runtime_put_sync() to invoke the > subsystem-level idle callback for the device at that time. > > The user space can effectively disallow the driver of the device to power manage > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
