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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Linux ACPI <linux-acpi@vger.kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Zhang Rui <rui.zhang@intel.com>,
        Mario Limonciello <mario.limonciello@amd.com>
Subject: [PATCH] ACPI: PM: s2idle: Use LPS0 idle if ACPI_FADT_LOW_POWER_S0 is unset
Date:   Wed, 13 Jul 2022 20:51:13 +0200
Message-ID: <12037674.O9o76ZdvQC@kreacher>
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

If the PNP0D80 device is present and its _DSM appears to be valid,
there is no reason to avoid using it even if ACPI_FADT_LOW_POWER_S0
is unset in the FADT, because suspend-to-idle may be the only way to
suspend the system if S3 is not supported by the platform, so do not
return early from lps0_device_attach() in that case.

However, still check ACPI_FADT_LOW_POWER_S0 when deciding whether or
not suspend-to-idle should be the default system suspend method.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/acpi/x86/s2idle.c |   11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/acpi/x86/s2idle.c
===================================================================
--- linux-pm.orig/drivers/acpi/x86/s2idle.c
+++ linux-pm/drivers/acpi/x86/s2idle.c
@@ -369,9 +369,6 @@ static int lps0_device_attach(struct acp
 	if (lps0_device_handle)
 		return 0;
 
-	if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0))
-		return 0;
-
 	if (acpi_s2idle_vendor_amd()) {
 		/* AMD0004, AMD0005, AMDI0005:
 		 * - Should use rev_id 0x0
@@ -421,10 +418,12 @@ static int lps0_device_attach(struct acp
 		lpi_device_get_constraints();
 
 	/*
-	 * Use suspend-to-idle by default if the default suspend mode was not
-	 * set from the command line.
+	 * Use suspend-to-idle by default if ACPI_FADT_LOW_POWER_S0 is set in
+	 * the FADT and the default suspend mode was not set from the command
+	 * line.
 	 */
-	if (mem_sleep_default > PM_SUSPEND_MEM && !acpi_sleep_default_s3)
+	if ((acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0) &&
+	    mem_sleep_default > PM_SUSPEND_MEM && !acpi_sleep_default_s3)
 		mem_sleep_current = PM_SUSPEND_TO_IDLE;
 
 	/*