ACPI: PM: x86: Print messages regarding LPS0 idle support

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@intel.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
index 974746e6e59d..ad4b2987b3d6 100644
--- a/drivers/acpi/sleep.c
+++ b/drivers/acpi/sleep.c
@@ -824,6 +824,9 @@ static const struct platform_s2idle_ops acpi_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);
 }