From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Because suspend-to-idle is always supported and on x86 it is the only
way to suspend the system if S3 is not supported by the platform, the
kernel attempts to enter low-power S0 idle in the suspend-to-idle flow
regardless of whether or not the ACPI_FADT_LOW_POWER_S0 flag is set in
the FADT. However, if that flag is not set, residency counters
associated with low-power S0 idle may not count and the platform may
refuse to put the EC into a low-power mode, for example.
For this reason, print diagnostic messages when the platform should
achieve significant energy savings in low-power S0 idle (because the
ACPI_FADT_LOW_POWER_S0 flag is set in the FADT) and when
suspend-to-idle becomes the default suspend method (because low-power
S0 idle should be equally or more efficient than S3, if available).
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
---
drivers/acpi/sleep.c | 3 +++
drivers/acpi/x86/s2idle.c | 4 +++-
2 files changed, 6 insertions(+), 1 deletion(-)
Index: linux-pm/drivers/acpi/sleep.c
===================================================================
--- linux-pm.orig/drivers/acpi/sleep.c
+++ linux-pm/drivers/acpi/sleep.c
@@ -824,6 +824,9 @@ static const struct platform_s2idle_ops
void __weak acpi_s2idle_setup(void)
{
+ if (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)
+ pr_info("Efficient low-power S0 idle declared\n");
+
s2idle_set_ops(&acpi_s2idle_ops);
}
Index: linux-pm/drivers/acpi/x86/s2idle.c
===================================================================
--- linux-pm.orig/drivers/acpi/x86/s2idle.c
+++ linux-pm/drivers/acpi/x86/s2idle.c
@@ -423,8 +423,10 @@ static int lps0_device_attach(struct acp
* line.
*/
if ((acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0) &&
- mem_sleep_default > PM_SUSPEND_MEM && !acpi_sleep_default_s3)
+ mem_sleep_default > PM_SUSPEND_MEM && !acpi_sleep_default_s3) {
mem_sleep_current = PM_SUSPEND_TO_IDLE;
+ pr_info("Low-power S0 idle used by default for system suspend\n");
+ }
/*
* Some LPS0 systems, like ASUS Zenbook UX430UNR/i7-8550U, require the
