dt-bindings: mfd: LMU: Add ti,brightness-resolution

Add ti,brightness-resolution to the TI LMU binding to define
whether the device uses 8-bit brightness or 11-bit brightness.
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

Documentation/devicetree/bindings/mfd/ti-lmu.txt

@@ -31,6 +31,16 @@ Optional properties:
   - ramp-down-us: Current ramping from one brightness level to
 		  the a lower brightness level.
 		  Range from 2048 us - 117.44 s
+  - ti,brightness-resolution - This determines whether to use 8 bit brightness
+			       mode or 11 bit brightness mode.  If this value is
+			       not set the device is defaulted to the preferred
+			       8bit brightness mode per 7.3.4.1 of the data
+			       sheet.  This setting can either be in the parent
+			       node or as part of the LED child nodes.  This
+			       is determined by the part itself if the strings
+			       have a common brightness register or individual
+			       brightness registers.
+			       The values are 255 (8bit) or 2047 (11bit).
 
 Required node:
   - backlight: All LMU devices have backlight child nodes.
@@ -217,6 +227,7 @@ lm3697@36 {
 		compatible = "ti,lm3697-backlight";
 
 		lcd {
+			ti,brightness-resolution = <255>;
 			led-sources = <0 1 2>;
 			ramp-up-us = <200000>;
 			ramp-down-us = <200000>;