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" <redacted>
Signed-off-by: Sudeep Holla <redacted>
---
 include/linux/suspend.h |  2 ++
 kernel/power/main.c     |  1 +
 kernel/power/suspend.c  | 14 +++++++++++---
 3 files changed, 14 insertions(+), 3 deletions(-)

v1->v2:
        - Introduced pm_freeze_init instead of (mis/re)using suspend_set_ops
          to setup freeze state in absense of registered platform suspend_ops

diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index 7693e39b14fe..0528ee32be7c 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h

@@ -245,6 +245,7 @@ static inline bool idle_should_freeze(void)
        return unlikely(suspend_freeze_state == FREEZE_STATE_ENTER);
 }

+extern void __init pm_freeze_init(void);
 extern void freeze_set_ops(const struct platform_freeze_ops *ops);
 extern void freeze_wake(void);

@@ -279,6 +280,7 @@ static inline bool pm_resume_via_firmware(void) { return false; }
 static inline void suspend_set_ops(const struct platform_suspend_ops *ops) {}
 static inline int pm_suspend(suspend_state_t state) { return -ENOSYS; }
 static inline bool idle_should_freeze(void) { return false; }
+static inline void __init pm_freeze_init(void) {}

 static inline void freeze_set_ops(const struct platform_freeze_ops *ops) {}
 static inline void freeze_wake(void) {}
 #endif /* !CONFIG_SUSPEND */

diff --git a/kernel/power/main.c b/kernel/power/main.c
index 5ea50b1b7595..f27c2f2d0f22 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c

@@ -651,6 +651,7 @@ static int __init pm_init(void)
        if (error)
                return error;
        pm_print_times_init();
+       pm_freeze_init();

        return pm_autosleep_init();
 }

diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 0acab9d7f96f..1c962a366678 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c

@@ -118,10 +118,18 @@ static bool valid_state(suspend_state_t state)
  */
 static bool relative_states;

+void __init pm_freeze_init(void)
+{
+       /*
+        * freeze state should be supported even without any suspend_ops,
+        * initialize pm_states accordingly here
+        */
+       pm_states[PM_SUSPEND_FREEZE] = pm_labels[relative_states ? 0 : 2];
+}
+
 static int __init sleep_states_setup(char *str)
 {
        relative_states = !strncmp(str, "1", 1);
-       pm_states[PM_SUSPEND_FREEZE] = pm_labels[relative_states ? 0 : 2];
        return 1;
 }

@@ -211,7 +219,7 @@ 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 +229,7 @@ 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();
 }

--