ACPI: platform-profile: call sysfs_notify() from platform_profile_store()

Drivers like thinkpad_acpi and ideapad_laptop call the
platform_profile_notify() helper when the profile is changed by hardware
(the embedded-controller/EC) in response to an EC handled hotkey.

This allows userspace to monitor for such changes by polling for POLLPRI
on the platform_profile sysfs file. But the profile can also be changed
underneath a userspace program monitoring it by anonther userspace program
storing a new value.

Add a sysfs_notify() call to platform_profile_store(), so that userspace
programs monitoring for changes also get notified in this case.

Also update the documentation to document that POLLPRI polling can be
used to watch for changes.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/ABI/testing/sysfs-platform_profile

@@ -26,3 +26,10 @@ Contact:	Hans de Goede <hdegoede@redhat.com>
 Description:	Reading this file gives the current selected profile for this
 		device. Writing this file with one of the strings from
 		platform_profile_choices changes the profile to the new value.
+
+		This file can be monitored for changes by polling for POLLPRI,
+		POLLPRI will be signalled on any changes, independent of those
+		changes coming from a userspace write; or coming from another
+		source such as e.g. a hotkey triggered profile change handled
+		either directly by the embedded-controller or fully handled
+		inside the kernel.

drivers/acpi/platform_profile.c

@@ -106,6 +106,9 @@ static ssize_t platform_profile_store(struct device *dev,
 	}
 
 	err = cur_profile->profile_set(cur_profile, i);
+	if (!err)
+		sysfs_notify(acpi_kobj, NULL, "platform_profile");
+
 	mutex_unlock(&profile_lock);
 	if (err)
 		return err;