This patch (as1308b) fixes __pm_runtime_get(). Currently the routine
will resume a device if the prior usage count was 0. But this isn't
right; thanks to pm_runtime_get_noresume() the usage count can be
positive even while the device is suspended.
Now the routine always tries to carry out a resume when called
synchronously. When called asynchronously, it avoids the overhead of
an unnecessary spinlock acquisition by doing the resume only if the
device's state was SUSPENDING or SUSPENDED. Since the access to the
state is unprotected, be careful to read the value only once.
Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
---
Although this probably isn't an important issue, it's a good idea to
avoid doing a double read of a value that might change while we're
looking at it.
I trust there is no problem in replacing the previous version of the
patch with this version.
Index: usb-2.6/drivers/base/power/runtime.c
===================================================================
--- usb-2.6.orig/drivers/base/power/runtime.c
+++ usb-2.6/drivers/base/power/runtime.c
@@ -703,16 +703,25 @@ EXPORT_SYMBOL_GPL(pm_request_resume);
* @dev: Device to handle.
* @sync: If set and the device is suspended, resume it synchronously.
*
- * Increment the usage count of the device and if it was zero previously,
- * resume it or submit a resume request for it, depending on the value of @sync.
+ * Increment the usage count of the device. If @sync is set, resume the device
+ * and wait for the resume to complete. Otherwise if the device is currently
+ * suspending or suspended, submit a resume request.
+ *
+ * If @sync is clear, the caller is responsible for synchronization.
*/
int __pm_runtime_get(struct device *dev, bool sync)
{
- int retval = 1;
+ int retval = 0;
- if (atomic_add_return(1, &dev->power.usage_count) == 1)
- retval = sync ? pm_runtime_resume(dev) : pm_request_resume(dev);
+ atomic_inc(&dev->power.usage_count);
+ if (sync) {
+ retval = pm_runtime_resume(dev);
+ } else {
+ enum rpm_status s = ACCESS_ONCE(dev->power.runtime_status);
+ if (s == RPM_SUSPENDING || s == RPM_SUSPENDED)
+ retval = pm_request_resume(dev);
+ }
return retval;
}
EXPORT_SYMBOL_GPL(__pm_runtime_get);
Index: usb-2.6/Documentation/power/runtime_pm.txt
===================================================================
--- usb-2.6.orig/Documentation/power/runtime_pm.txt
+++ usb-2.6/Documentation/power/runtime_pm.txt
@@ -276,8 +276,9 @@ drivers/base/power/runtime.c and include
- increment the device's usage counter
int pm_runtime_get(struct device *dev);
- - increment the device's usage counter, run pm_request_resume(dev) and
- return its result
+ - increment the device's usage counter; if the device is currently
+ suspending or suspended then run pm_request_resume(dev) and return its
+ result
int pm_runtime_get_sync(struct device *dev);
- increment the device's usage counter, run pm_runtime_resume(dev) and
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