Revert "PM / sleep / ACPI: Use the ACPI_FADT_LOW_POWER_S0 flag"

Revert commit 08b98d3291 (PM / sleep / ACPI: Use the ACPI_FADT_LOW_POWER_S0
flag) as it caused system suspend (in the default configuration) to fail
on Dell XPS13 (9360) with the Kaby Lake processor.

Fixes: 08b98d3291 (PM / sleep / ACPI: Use the ACPI_FADT_LOW_POWER_S0 flag)
Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/power/states.txt

@@ -35,9 +35,7 @@ only one way to cause the system to go into the Suspend-To-RAM state (write
 The default suspend mode (ie. the one to be used without writing anything into
 /sys/power/mem_sleep) is either "deep" (if Suspend-To-RAM is supported) or
 "s2idle", but it can be overridden by the value of the "mem_sleep_default"
-parameter in the kernel command line.  On some ACPI-based systems, depending on
-the information in the FADT, the default may be "s2idle" even if Suspend-To-RAM
-is supported.
+parameter in the kernel command line.
 
 The properties of all of the sleep states are described below.
 

drivers/acpi/sleep.c

@@ -691,14 +691,6 @@ static void acpi_sleep_suspend_setup(void)
 		if (acpi_sleep_state_supported(i))
 			sleep_states[i] = 1;
 
-	/*
-	 * Use suspend-to-idle by default if ACPI_FADT_LOW_POWER_S0 is set and
-	 * the default suspend mode was not selected from the command line.
-	 */
-	if (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0 &&
-	    mem_sleep_default > PM_SUSPEND_MEM)
-		mem_sleep_default = PM_SUSPEND_FREEZE;
-
 	suspend_set_ops(old_suspend_ordering ?
 		&acpi_suspend_ops_old : &acpi_suspend_ops);
 	freeze_set_ops(&acpi_freeze_ops);

include/linux/suspend.h

@@ -194,8 +194,6 @@ struct platform_freeze_ops {
 };
 
 #ifdef CONFIG_SUSPEND
-extern suspend_state_t mem_sleep_default;
-
 /**
  * suspend_set_ops - set platform dependent suspend operations
  * @ops: The new suspend operations to set.

kernel/power/suspend.c

@@ -46,7 +46,7 @@ static const char * const mem_sleep_labels[] = {
 const char *mem_sleep_states[PM_SUSPEND_MAX];
 
 suspend_state_t mem_sleep_current = PM_SUSPEND_FREEZE;
-suspend_state_t mem_sleep_default = PM_SUSPEND_MAX;
+static suspend_state_t mem_sleep_default = PM_SUSPEND_MEM;
 
 unsigned int pm_suspend_global_flags;
 EXPORT_SYMBOL_GPL(pm_suspend_global_flags);
@@ -168,7 +168,7 @@ void suspend_set_ops(const struct platform_suspend_ops *ops)
 	}
 	if (valid_state(PM_SUSPEND_MEM)) {
 		mem_sleep_states[PM_SUSPEND_MEM] = mem_sleep_labels[PM_SUSPEND_MEM];
-		if (mem_sleep_default >= PM_SUSPEND_MEM)
+		if (mem_sleep_default == PM_SUSPEND_MEM)
 			mem_sleep_current = PM_SUSPEND_MEM;
 	}