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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Linux ACPI <linux-acpi@vger.kernel.org>
Cc:     Alessandro Zummo <a.zummo@towertech.it>,
        LKML <linux-kernel@vger.kernel.org>,
        Zhang Rui <rui.zhang@intel.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        linux-rtc@vger.kernel.org, Linux PM <linux-pm@vger.kernel.org>
Subject: [PATCH v2] rtc: rtc-cmos: Do not check ACPI_FADT_LOW_POWER_S0
Date:   Mon, 08 Aug 2022 20:23:59 +0200
Message-ID: <12054246.O9o76ZdvQC@kreacher>
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.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.

Accordingly, drop the ACPI_FADT_LOW_POWER_S0 check from
use_acpi_alarm_quirks().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
---

-> v2:
   * Fix typo in the changelog.
   * Add R-by tag from Mario.

---
 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;