PM / Driver core: leave runtime PM enabled during system shutdown

Disabling all runtime PM during system shutdown turns out not to be a
good idea, because some devices may need to be woken up from a
low-power state at that time.

The whole point of disabling runtime PM for system shutdown was to
prevent untimely runtime-suspend method calls.  This patch (as1504)
accomplishes the same result by incrementing the usage count for each
device and waiting for ongoing runtime-PM callbacks to finish.  This
is what we already do during system suspend and hibernation, which
makes sense since the shutdown method is pretty much a legacy analog
of the pm->poweroff method.

This fixes a recent regression on some OMAP systems introduced by
commit af8db1508f2c9f3b6e633e2d2d906c6557c617f9 (PM / driver core:
disable device's runtime PM during shutdown).

Reported-and-tested-by: NeilBrown <neilb@suse.de>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

diff --git a/drivers/base/core.c b/drivers/base/core.c
index d8b3d89..919daa7 100644 (file)
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1743,8 +1743,10 @@ void device_shutdown(void)
                 */
                list_del_init(&dev->kobj.entry);
                spin_unlock(&devices_kset->list_lock);
-               /* Disable all device's runtime power management */
-               pm_runtime_disable(dev);
+
+               /* Don't allow any more runtime suspends */
+               pm_runtime_get_noresume(dev);
+               pm_runtime_barrier(dev);
 
                if (dev->bus && dev->bus->shutdown) {
                        dev_dbg(dev, "shutdown\n");