atmel_lcdfb: backlight control

On the sam9 EK boards, the LCD backlight is hooked up to a PWM output from
the LCD controller.  It's controlled by "contrast" registers though.

This patch lets boards declare that they have that kind of backlight
control.  The driver can then export this control, letting screenblank and
other operations actually take effect ...  reducing the typically
substantial power drain from the backlight.

Note that it's not fully cooked
  - doesn't force backlight off during system suspend
  - the "power" and "blank" events may not be done right
This should be easily added in the future.

[nicolas.ferre@atmel.com: remove unneeded inline and rename functions]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Andrew Victor <linux@maxim.org.za>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index 9609a6c676be..924e2551044a 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -50,6 +50,19 @@ config BACKLIGHT_CLASS_DEVICE
           To have support for your specific LCD panel you will have to
           select the proper drivers which depend on this option.
 
+config BACKLIGHT_ATMEL_LCDC
+        bool "Atmel LCDC Contrast-as-Backlight control"
+        depends on BACKLIGHT_CLASS_DEVICE && FB_ATMEL
+        default y if MACH_SAM9261EK || MACH_SAM9263EK
+        help
+          This provides a backlight control internal to the Atmel LCDC
+          driver.  If the LCD "contrast control" on your board is wired
+          so it controls the backlight brightness, select this option to
+          export this as a PWM-based backlight control.
+
+          If in doubt, it's safe to enable this option; it doesn't kick
+          in unless the board's description says it's wired that way.
+
 config BACKLIGHT_CORGI
         tristate "Generic (aka Sharp Corgi) Backlight Driver"
         depends on BACKLIGHT_CLASS_DEVICE