PM / Domains: Take .power_off() error code into account

Currently pm_genpd_poweroff() discards error codes returned by
the PM domain's .power_off() callback, because it's safer to always
regard the domain as inaccessible to drivers after a failing
.power_off().  Still, there are situations in which the low-level
code may want to indicate that it doesn't want to power off the
domain, so allow it to do that by returning -EBUSY from .power_off().

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Magnus Damm <damm@opensource.se>

drivers/base/power/domain.c

@@ -312,8 +312,16 @@ static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
 		}
 	}
 
-	if (genpd->power_off)
-		genpd->power_off(genpd);
+	if (genpd->power_off) {
+		ret = genpd->power_off(genpd);
+		if (ret == -EBUSY) {
+			genpd_set_active(genpd);
+			if (parent)
+				genpd_release_lock(parent);
+
+			goto out;
+		}
+	}
 
 	genpd->status = GPD_STATE_POWER_OFF;