[PATCH] PM / sleep: enable suspend-to-idle even without registered suspend_ops

[Sudeep Holla <sudeep.holla@arm.com>]

Suspend-to-idle (aka the "freeze" sleep state) is a system sleep state
in which all of the processors enter deepest possible idle state and
wait for interrupts right after suspending all the devices.

There is no hard requirement for a platform to support and register
platform specific suspend_ops to enter suspend-to-idle/freeze state.
Only deeper system sleep states like PM_SUSPEND_STANDBY and
PM_SUSPEND_MEM rely on such low level support/implementation.

suspend-to-idle can be entered as along as all the devices can be
suspended. This patch enables the support for suspend-to-idle even on
systems that don't have any low level support for deeper system sleep
states and/or don't register any platform specific suspend_ops.

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
 kernel/power/main.c    | 5 +++++
 kernel/power/suspend.c | 8 +++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

Hi Rafael,

I am not sure if you like this approach. I found this to be the simplest
but I may have missed to consider all possible corner cases especially
for x86 and other platforms. I don't see any such issues/cases with ARM
systems.

Regards,
Sudeep

diff --git a/kernel/power/main.c b/kernel/power/main.c
index 5ea50b1b7595..0f0fd9184f39 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -651,6 +651,11 @@ static int __init pm_init(void)
 	if (error)
 		return error;
 	pm_print_times_init();
+	/*
+	 * freeze state should be supported even without any suspend_ops,
+	 * calling suspend_set_ops without any ops will setup freeze state
+	 */
+	suspend_set_ops(NULL);
 	return pm_autosleep_init();
 }

diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 0acab9d7f96f..37d64f811ecd 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -138,7 +138,9 @@ void suspend_set_ops(const struct platform_suspend_ops *ops)

 	lock_system_sleep();

-	suspend_ops = ops;
+	WARN_ONCE(ops && suspend_ops, "overriding suspend_ops");
+	if (ops)
+		suspend_ops = ops;
 	for (i = PM_SUSPEND_MEM; i >= PM_SUSPEND_STANDBY; i--)
 		if (valid_state(i)) {
 			pm_states[i] = pm_labels[j++];
@@ -211,7 +213,7 @@ static int platform_suspend_begin(suspend_state_t state)
 {
 	if (state == PM_SUSPEND_FREEZE && freeze_ops && freeze_ops->begin)
 		return freeze_ops->begin();
-	else if (suspend_ops->begin)
+	else if (suspend_ops && suspend_ops->begin)
 		return suspend_ops->begin(state);
 	else
 		return 0;
@@ -221,7 +223,7 @@ static void platform_resume_end(suspend_state_t state)
 {
 	if (state == PM_SUSPEND_FREEZE && freeze_ops && freeze_ops->end)
 		freeze_ops->end();
-	else if (suspend_ops->end)
+	else if (suspend_ops && suspend_ops->end)
 		suspend_ops->end();
 }

--
2.7.4