linux-kernel - Re: [PATCH] rtc: rtc-cmos: Do not check ACPI_FADT_LOW_POWER

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Message-ID: <f253a352-caf3-49fb-17d3-0265b472d4c6@amd.com>
Date:   Fri, 5 Aug 2022 12:29:34 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Zhang Rui <rui.zhang@...el.com>, linux-rtc@...r.kernel.org,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] rtc: rtc-cmos: Do not check ACPI_FADT_LOW_POWER_S0

On 8/5/2022 12:27, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The ACPI_FADT_LOW_POWER_S0 flag merely means that it is better to
> use low-power S0 idle on the given platform than S3 (provided that
> the latter is supported) and it doesn't preclude using either of
> them (which of them will be used depends on the choices made by user
> space).
> 
> For this reason, there is no benefit from checking that flag in
> use_acpi_alarm_quirks().
> 
> First off, it cannot be a bug to do S3 with use_acpi_alarm set,
> because S3 can be used on systems with ACPI_FADT_LOW_POWER_S0 and it
> must work if really supported, so the ACPI_FADT_LOW_POWER_S0 check is
> not needed to protect the S3-capable systems from failing.
> 
> Second, suspend-to-idle can be carried out on a system with
> ACPI_FADT_LOW_POWER_S0 unset and it is expected to work, so if setting
> use_acpi_alarm is needed to handle that case correctly, it should be
> set regardless of the ACPI_FADT_LOW_POWER_S0 value.
> 
> Accodringly, drop the ACPI_FADT_LOW_POWER_S0 check from

s/Accodringly/ ccordingly/

> use_acpi_alarm_quirks().
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

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

> ---
>   drivers/rtc/rtc-cmos.c |    3 ---
>   1 file changed, 3 deletions(-)
> 
> Index: linux-pm/drivers/rtc/rtc-cmos.c
> ===================================================================
> --- linux-pm.orig/drivers/rtc/rtc-cmos.c
> +++ linux-pm/drivers/rtc/rtc-cmos.c
> @@ -1260,9 +1260,6 @@ static void use_acpi_alarm_quirks(void)
>   	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
>   		return;
>   
> -	if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0))
> -		return;
> -
>   	if (!is_hpet_enabled())
>   		return;
>   
> 
> 
>