linux-kernel - Re: [PATCH] intel: thermal: PCH: Drop ACPI_FADT_LOW_POWER

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Date:   Sun, 17 Jul 2022 14:14:42 +0800
From:   Zhang Rui <rui.zhang@...el.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Cc:     Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mario Limonciello <mario.limonciello@....com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH] intel: thermal: PCH: Drop ACPI_FADT_LOW_POWER_S0 check

On Thu, 2022-07-14 at 21:11 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> If ACPI_FADT_LOW_POWER_S0 is not set, this doesn't mean that low-
> power
> S0 idle is not usable.  It merely means that using S3 on the given
> system is more beneficial from the energy saving perspective than
> using
> low-power S0 idle, as long as S3 is supported.

Agreed.

> 
> Suspend-to-idle is still a valid suspend mode if
> ACPI_FADT_LOW_POWER_S0
> is not set and the pm_suspend_via_firmware() check in
> pch_wpt_suspend()
> is sufficient to distinguish suspend-to-idle from S3, so drop the
> confusing ACPI_FADT_LOW_POWER_S0 check.

the cooling delay in the suspend callback is to make sure PCH
temperature won't block S0ix during s2idle. So if S0ix is not
supported, it is meaningless to invoke the cooling delay during s2idle.

so the problem is that we don't have an indicator for S0ix capability.
And this also applies to drivers/rtc/rtc-cmos.c, where we use ACPI SCI
for runtime RTC wakeup instead of HPET interrupt on "S0ix capable"
platforms because the HPET timer may block S0ix.

thanks,
rui

> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/thermal/intel/intel_pch_thermal.c |    8 --------
>  1 file changed, 8 deletions(-)
> 
> Index: linux-pm/drivers/thermal/intel/intel_pch_thermal.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/intel/intel_pch_thermal.c
> +++ linux-pm/drivers/thermal/intel/intel_pch_thermal.c
> @@ -207,14 +207,6 @@ static int pch_wpt_suspend(struct pch_th
>                 return 0;
>         }
>  
> -       /* Do not check temperature if it is not a S0ix capable
> platform */
> -#ifdef CONFIG_ACPI
> -       if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0))
> -               return 0;
> -#else
> -       return 0;
> -#endif
> -
>         /* Do not check temperature if it is not s2idle */
>         if (pm_suspend_via_firmware())
>                 return 0;
> 
> 
>