PM: sleep: Unblock runtime PM when device prepare fails

device_prepare() blocks runtime PM for a device with runtime PM disabled
before invoking its system-sleep ->prepare() callback. For a device that
has never enabled runtime PM, this changes dev->power.last_status from
RPM_INVALID to RPM_BLOCKED.

If the callback returns an error, dpm_prepare() does not move the device
to dpm_prepared_list. Consequently, the recovery path through
dpm_complete() never calls device_complete() for the failing device.

The error path drops the runtime PM usage reference, but does not clear
RPM_BLOCKED. A later legitimate pm_runtime_enable() then reports:

  Attempt to enable runtime PM when it is blocked

before clearing the stale state.

Call pm_runtime_unblock() on the prepare error path before dropping the
runtime PM reference, matching the cleanup performed by device_complete().

The issue was reproduced with a platform test device whose ->prepare()
callback returns -EIO while runtime PM has never been enabled. Before
the fix, last_status remained RPM_BLOCKED after the failed suspend and
the first pm_runtime_enable() produced the warning above. With the fix,
last_status is restored to RPM_INVALID and the warning is absent.

Fixes: 3e5eee147b ("PM: Block enabling of runtime PM during system suspend")
Cc: All applicable <[email protected]>
Signed-off-by: Shibo Zhu <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Rafael J. Wysocki <[email protected]>

drivers/base/power/main.c

@@ -2248,6 +2248,7 @@ unlock:
 
 	if (ret < 0) {
 		suspend_report_result(dev, callback, ret);
+		pm_runtime_unblock(dev);
 		pm_runtime_put(dev);
 		return ret;
 	}