[PATCH] ACPI: PM: x86: Print messages regarding LPS0 idle support

[PATCH] ACPI: PM: x86: Print messages regarding LPS0 idle support

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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>
---
 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

Re: [PATCH] ACPI: PM: x86: Print messages regarding LPS0 idle support

[Limonciello, Mario]

On 7/21/2022 11:13, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> 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>

> ---
>   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
> 
> 
>