pm/sleep: Add PM_USERSPACE_AUTOSLEEP Kconfig

Systems that initiate frequent suspend/resume from userspace
can make the kernel aware by enabling PM_USERSPACE_AUTOSLEEP
config.

This allows for certain sleep-sensitive code (wireguard/rng) to
decide on what preparatory work should be performed (or not) in
their pm_notification callbacks.

This patch was prompted by the discussion at [1] which attempts
to remove CONFIG_ANDROID that currently guards these code paths.

[1] https://lore.kernel.org/r/20220629150102.1582425-1-hch@lst.de/Suggested-by: NJason A. Donenfeld <Jason@zx2c4.com>
Acked-by: NJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: NKalesh Singh <kaleshsingh@google.com>
Link: https://lore.kernel.org/r/20220630191230.235306-1-kaleshsingh@google.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/random.c

@@ -755,8 +755,8 @@ static int random_pm_notification(struct notifier_block *nb, unsigned long actio
 	spin_unlock_irqrestore(&input_pool.lock, flags);
 
 	if (crng_ready() && (action == PM_RESTORE_PREPARE ||
-	    (action == PM_POST_SUSPEND &&
-	     !IS_ENABLED(CONFIG_PM_AUTOSLEEP) && !IS_ENABLED(CONFIG_ANDROID)))) {
+	    (action == PM_POST_SUSPEND && !IS_ENABLED(CONFIG_PM_AUTOSLEEP) &&
+	     !IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP)))) {
 		crng_reseed();
 		pr_notice("crng reseeded on system resumption\n");
 	}

drivers/net/wireguard/device.c

@@ -69,7 +69,8 @@ static int wg_pm_notification(struct notifier_block *nb, unsigned long action, v
 	 * its normal operation rather than as a somewhat rare event, then we
 	 * don't actually want to clear keys.
 	 */
-	if (IS_ENABLED(CONFIG_PM_AUTOSLEEP) || IS_ENABLED(CONFIG_ANDROID))
+	if (IS_ENABLED(CONFIG_PM_AUTOSLEEP) ||
+	    IS_ENABLED(CONFIG_PM_USERSPACE_AUTOSLEEP))
 		return 0;
 
 	if (action != PM_HIBERNATION_PREPARE && action != PM_SUSPEND_PREPARE)

kernel/power/Kconfig

@@ -143,6 +143,26 @@ config PM_AUTOSLEEP
 	Allow the kernel to trigger a system transition into a global sleep
 	state automatically whenever there are no active wakeup sources.
 
+config PM_USERSPACE_AUTOSLEEP
+	bool "Userspace opportunistic sleep"
+	depends on PM_SLEEP
+	help
+	Notify kernel of aggressive userspace autosleep power management policy.
+
+	This option changes the behavior of various sleep-sensitive code to deal
+	with frequent userspace-initiated transitions into a global sleep state.
+
+	Saying Y here, disables code paths that most users really should keep
+	enabled. In particular, only enable this if it is very common to be
+	asleep/awake for very short periods of time (<= 2 seconds).
+
+	Only platforms, such as Android, that implement opportunistic sleep from
+	a userspace power manager service should enable this option; and not
+	other machines. Therefore, you should say N here, unless you are
+	extremely certain that this is what you want. The option otherwise has
+	bad, undesirable effects, and should not be enabled just for fun.
+
+
 config PM_WAKELOCKS
 	bool "User space wakeup sources interface"
 	depends on PM_SLEEP