backlight: add backlight type
There may be multiple ways of controlling the backlight on a given
machine. Allow drivers to expose the type of interface they are
providing, making it possible for userspace to make appropriate policy
decisions.
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: David Airlie <airlied@linux.ie>
Cc: Alex Deucher <alexdeucher@gmail.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/ABI/stable/sysfs-class-backlight b/Documentation/ABI/stable/sysfs-class-backlight
index 4d637e1..70302f3 100644
--- a/Documentation/ABI/stable/sysfs-class-backlight
+++ b/Documentation/ABI/stable/sysfs-class-backlight
@@ -34,3 +34,23 @@
Description:
Maximum brightness for <backlight>.
Users: HAL
+
+What: /sys/class/backlight/<backlight>/type
+Date: September 2010
+KernelVersion: 2.6.37
+Contact: Matthew Garrett <mjg@redhat.com>
+Description:
+ The type of interface controlled by <backlight>.
+ "firmware": The driver uses a standard firmware interface
+ "platform": The driver uses a platform-specific interface
+ "raw": The driver controls hardware registers directly
+
+ In the general case, when multiple backlight
+ interfaces are available for a single device, firmware
+ control should be preferred to platform control should
+ be preferred to raw control. Using a firmware
+ interface reduces the probability of confusion with
+ the hardware and the OS independently updating the
+ backlight state. Platform interfaces are mostly a
+ holdover from pre-standardisation of firmware
+ interfaces.