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

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Message-ID: <c3b142ff-4a54-036d-320d-0b74410ba825@amd.com>
Date:   Thu, 21 Jul 2022 14:55:17 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH] ACPI: PM: x86: Print messages regarding LPS0 idle support

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

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