[PATCH RFC 1/3] pmdomain: core: Add a helper to power on the restart devices

[Claudiu]

From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>

Restart devices (e.g., watchdog) may be part of a software-controlled power
domain. In the case of watchdog devices, if they implement the
struct watchdog::restart() API, this is called though:

kernel_restart() ->
  machine_restart() ->
    do_kernel_restart() ->
      atomic_notifier_call_chain() ->
        watchdog_restart_notifier()

The watchdog_restart_notifier() is called with local interrupts disabled
and SMP disabled (machine_restart() calls local_irq_disable() and
smp_send_stop() before calling do_kernel_restart()).

If the restart device (e.g., watchdog) is part of a software-controlled
power domain and this domain is off at the moment of restart, we need to
power it on before configuring the watchdog device.

Add the dev_pm_genpd_resume_restart_dev() function to power on a restart
device in these scenarios.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
---
 drivers/pmdomain/core.c   | 18 ++++++++++++++++++
 include/linux/pm_domain.h |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index 83d978743659..d05bd72f6cfe 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -1540,6 +1540,24 @@ void dev_pm_genpd_resume(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(dev_pm_genpd_resume);
 
+/**
+ * dev_pm_genpd_resume_restart_dev - Try to synchronously resume the genpd for
+ * a reset device
+ * @dev: The reset device that is attached to the genpd, which needs to be
+ * resumed.
+ *
+ * This routine should tipicaly be called for a restart device (e.g. watchdog)
+ * that needs to be resumed during system restart phase.
+ */
+void dev_pm_genpd_resume_restart_dev(struct device *dev)
+{
+	if (system_state != SYSTEM_RESTART)
+		return;
+
+	dev_pm_genpd_resume(dev);
+}
+EXPORT_SYMBOL_GPL(dev_pm_genpd_resume_restart_dev);
+
 #else /* !CONFIG_PM_SLEEP */
 
 #define genpd_prepare		NULL
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index 71e4f0fb8867..9f8ecfa0bf3c 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -347,9 +347,11 @@ static inline void dev_pm_genpd_synced_poweroff(struct device *dev)
 #ifdef CONFIG_PM_GENERIC_DOMAINS_SLEEP
 void dev_pm_genpd_suspend(struct device *dev);
 void dev_pm_genpd_resume(struct device *dev);
+void dev_pm_genpd_resume_restart_dev(struct device *dev);
 #else
 static inline void dev_pm_genpd_suspend(struct device *dev) {}
 static inline void dev_pm_genpd_resume(struct device *dev) {}
+static inline void dev_pm_genpd_resume_restart_dev(struct device *dev) {}
 #endif
 
 /* OF PM domain providers */
-- 
2.39.2