[v2,1/2] cpuidle: Do not return from cpuidle_play_dead() on callback failures

Commit Message

Rafael J. Wysocki Nov. 15, 2024, 8:58 p.m. UTC

From: Rafael J. Wysocki <[e-mail]>

If the :enter_dead() idle state callback fails for a certain state,
there may be still a shallower state for which it will work.

Because the only caller of cpuidle_play_dead(), native_play_dead(),
falls back to hlt_play_dead() if it returns an error, it should
better try all of the idle states for which :enter_dead() is present
before failing, so change it accordingly.

Also notice that the :enter_dead() state callback is not expected
to return on success (the CPU should be "dead" then), so make
cpuidle_play_dead() ignore its return value.

Signed-off-by: Rafael J. Wysocki <[e-mail]>
Reviewed-by: Mario Limonciello <[e-mail]>
Tested-by: Mario Limonciello <[e-mail]> # 6.12-rc7
---

v1 -> v2:
   * Make cpuidle_play_dead() never return 0.
   * Add tags from Mario (I have added them because the change of the patch
     should not make a practical difference, but if you want them to be
     dropped, please let me know).

---
 drivers/cpuidle/cpuidle.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Patch

Index: linux-pm/drivers/cpuidle/cpuidle.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/cpuidle.c
+++ linux-pm/drivers/cpuidle/cpuidle.c
@@ -69,11 +69,15 @@  int cpuidle_play_dead(void)
 	if (!drv)
 		return -ENODEV;
 
-	/* Find lowest-power state that supports long-term idle */
-	for (i = drv->state_count - 1; i >= 0; i--)
+	for (i = drv->state_count - 1; i >= 0; i--) {
 		if (drv->states[i].enter_dead)
-			return drv->states[i].enter_dead(dev, i);
+			drv->states[i].enter_dead(dev, i);
+	}
 
+	/*
+	 * If :enter_dead() is successful, it will never return, so reaching
+	 * here means that all of them failed above or were not present.
+	 */
 	return -ENODEV;
 }