ACPI: Export FADT pm_profile integer value to userspace

There are a lot userspace approaches to detect the usage of the
platform (laptop, workstation, server, ...) and adjust kernel tunables
accordingly (io/process scheduler, power management, ...).

These approaches need constant maintaining and are ugly to implement
(detect PCMCIA controller -> laptop,
does not work on recent systems anymore, ...)
On ACPI systems there is an easy and reliable way (if implemented
in BIOS and most recent platforms have this value set).
-> export it to userspace.

Signed-off-by: Thomas Renninger <[email protected]>
Acked-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: Len Brown <[email protected]>

Documentation/ABI/stable/sysfs-acpi-pmprofile

@@ -0,0 +1,22 @@
+What: 		/sys/firmware/acpi/pm_profile
+Date:		03-Nov-2011
+KernelVersion:	v3.2
+Contact:	[email protected]
+Description: 	The ACPI pm_profile sysfs interface exports the platform
+		power management (and performance) requirement expectations
+		as provided by BIOS. The integer value is directly passed as
+		retrieved from the FADT ACPI table.
+Values:         For possible values see ACPI specification:
+		5.2.9 Fixed ACPI Description Table (FADT)
+		Field: Preferred_PM_Profile
+
+		Currently these values are defined by spec:
+		0 Unspecified
+		1 Desktop
+		2 Mobile
+		3 Workstation
+		4 Enterprise Server
+		5 SOHO Server
+		6 Appliance PC
+		7 Performance Server
+		>7 Reserved

drivers/acpi/sysfs.c

@@ -706,11 +706,23 @@ static void __exit interrupt_stats_exit(void)
 	return;
 }
 
+static ssize_t
+acpi_show_profile(struct device *dev, struct device_attribute *attr,
+		  char *buf)
+{
+	return sprintf(buf, "%d\n", acpi_gbl_FADT.preferred_profile);
+}
+
+static const struct device_attribute pm_profile_attr =
+	__ATTR(pm_profile, S_IRUGO, acpi_show_profile, NULL);
+
 int __init acpi_sysfs_init(void)
 {
 	int result;
 
 	result = acpi_tables_sysfs_init();
-
+	if (result)
+		return result;
+	result = sysfs_create_file(acpi_kobj, &pm_profile_attr.attr);
 	return result;
 }