[RFC v1 7/8] PM: hibernate: Enter s2idle sleep state before hibernation

[Antheas Kapenekakis <lkml@antheas.dev>]

Implement the standby states as part of hibernation. Specifically,
ensure we are in the inactive state before hibernation entry, and
sync the state as active after hibernation resume. In case of a failed
hibernation, restore the previous standby state.

Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
---
 kernel/power/hibernate.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index af8d07bafe02..85a5ca8f6537 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -787,7 +787,11 @@ static int load_image_and_restore(void)
  */
 int hibernate(void)
 {
+#ifdef CONFIG_SUSPEND
+	standby_state_t previous_standby;
+#endif
 	bool snapshot_test = false;
+	bool powered_down = false;
 	unsigned int sleep_flags;
 	int error;
 
@@ -815,6 +819,13 @@ int hibernate(void)
 	}
 
 	pr_info("hibernation entry\n");
+
+#if CONFIG_SUSPEND
+	/* Enter the standby screen off state in case userspace has not. */
+	previous_standby = pm_standby_get_state();
+	pm_standby_transition(PM_STANDBY_INACTIVE);
+#endif
+
 	pm_prepare_console();
 	error = pm_notifier_call_chain_robust(PM_HIBERNATION_PREPARE, PM_POST_HIBERNATION);
 	if (error)
@@ -867,10 +878,12 @@ int hibernate(void)
 		error = swsusp_write(flags);
 		swsusp_free();
 		if (!error) {
-			if (hibernation_mode == HIBERNATION_TEST_RESUME)
+			if (hibernation_mode == HIBERNATION_TEST_RESUME) {
 				snapshot_test = true;
-			else
+			} else {
+				powered_down = true;
 				power_down();
+			}
 		}
 		in_suspend = 0;
 		pm_restore_gfp_mask();
@@ -897,6 +910,18 @@ int hibernate(void)
  Notify:
 	pm_notifier_call_chain(PM_POST_HIBERNATION);
  Restore:
+#if CONFIG_SUSPEND
+	/*
+	 * If we resumed from S5, we are in the active standby state. However,
+	 * the kernel restored a stale value. Sync it. Otherwise, in e.g., the
+	 * case of a failed hibernation, transition to the previous value.
+	 */
+	if (powered_down)
+		pm_standby_set_state(PM_STANDBY_ACTIVE);
+	else
+		pm_standby_transition(previous_standby);
+#endif
+
 	pm_restore_console();
 	hibernate_release();
  Unlock:
-- 
2.52.0