drm/i915: panel: invert brightness via quirk

A machine may need to invert the panel backlight brightness value. This
patch adds the infrastructure for a quirk to do so.

Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 11 insertions, 6 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9f6ba8fab088..da449991e8ae 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -967,14 +967,19 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
         i8k.restricted  [HW] Allow controlling fans only if SYS_ADMIN
                         capability is set.
 
-        i915.invert_brightness
+        i915.invert_brightness=
                         [DRM] Invert the sense of the variable that is used to
                         set the brightness of the panel backlight. Normally a
-                        value of 0 indicates backlight switched off, and the
-                        maximum value sets the backlight to maximum brightness.
-                        If this parameter is specified, a value of 0 sets the
-                        backlight to maximum brightness, and the maximum value
-                        switches the backlight off.
+                        brightness value of 0 indicates backlight switched off,
+                        and the maximum of the brightness value sets the backlight
+                        to maximum brightness. If this parameter is set to 0
+                        (default) and the machine requires it, or this parameter
+                        is set to 1, a brightness value of 0 sets the backlight
+                        to maximum brightness, and the maximum of the brightness
+                        value switches the backlight off.
+                        -1 -- never invert brightness
+                         0 -- machine default
+                         1 -- force brightness inversion
 
         icn=            [HW,ISDN]
                         Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]