Re: [EXT] Re: [PATCH] nvme: Add abrupt shutdown support

[Keith Busch]

On Tue, Jul 06, 2021 at 08:14:45AM +0000, Shivamurthy Shastri (sshivamurthy) wrote:
> > Is it the device that wants an abrupt shutdown or the platform? If the
> > platform's power is running on limited back-up supply, and could inform
> > the kernel's power management subsystem of this, then a driver could use
> > that to determine if the quick shutdown is appropriate.
> 
> Yes, the platform is running on limited back-up supply. In this case, abrupt shutdown
> option will help to achieve shutdown with relatively low back-up requirements.
> 
> Please let me know if you want to include the abrupt shutdown as part of 
> 
> static const struct dev_pm_ops nvme_dev_pm_ops = {
> 	.suspend	= nvme_suspend,
>                .....

Are you suggesting creating a new pm callback just for this? I don't
think that's necessary.

I was considering just adding a bit to the pm_suspend_global_flags,
something like the patch below. You just have to fill in the platform
specific parts to set the flag.

---
diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index 8af13ba60c7e..f43c0b2313d0 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -210,9 +210,10 @@ extern int suspend_valid_only_mem(suspend_state_t state);
 
 extern unsigned int pm_suspend_global_flags;
 
-#define PM_SUSPEND_FLAG_FW_SUSPEND	BIT(0)
-#define PM_SUSPEND_FLAG_FW_RESUME	BIT(1)
-#define PM_SUSPEND_FLAG_NO_PLATFORM	BIT(2)
+#define PM_SUSPEND_FLAG_FW_SUSPEND		BIT(0)
+#define PM_SUSPEND_FLAG_FW_RESUME		BIT(1)
+#define PM_SUSPEND_FLAG_NO_PLATFORM		BIT(2)
+#define PM_SUSPEND_FLAG_POWER_LOSS_IMMINENT	BIT(3)
 
 static inline void pm_suspend_clear_flags(void)
 {
@@ -234,6 +235,11 @@ static inline void pm_set_suspend_no_platform(void)
 	pm_suspend_global_flags |= PM_SUSPEND_FLAG_NO_PLATFORM;
 }
 
+static inline void pm_set_power_loss_imminent(void)
+{
+	pm_suspend_global_flags |= PM_SUSPEND_FLAG_POWER_LOSS_IMMINENT;
+}
+
 /**
  * pm_suspend_via_firmware - Check if platform firmware will suspend the system.
  *
@@ -291,6 +297,21 @@ static inline bool pm_suspend_no_platform(void)
 	return !!(pm_suspend_global_flags & PM_SUSPEND_FLAG_NO_PLATFORM);
 }
 
+/**
+ * pm_power_loss_imminent - Check if platform is running on limited backup
+ * 			    power source
+ *
+ * To be called during system-wide power management transitions to sleep states.
+ *
+ * Return 'true' if power loss may be imminent due to platform running on
+ * limited backup supply. If set during a shutdown, drivers should use any
+ * available shortcuts to prepare their device for abrupt power loss.
+ */
+static inline bool pm_power_loss_imminent(void)
+{
+	return !!(pm_suspend_global_flags & PM_SUSPEND_FLAG_POWER_LOSS_IMMINENT);
+}
+
 /* Suspend-to-idle state machnine. */
 enum s2idle_states {
 	S2IDLE_STATE_NONE,      /* Not suspended/suspending. */
--