ACPI: video: create "brightness_switch_enabled" modparam

Introduce new module parameter for brightness control.
"brightness_switch_enabled" is set by default which means
nothing changes upon brightness switch events.

When "brightness_switch_enabled" is cleared via
"echo 0 > /sys/module/video/parameters/brightness_switch_enabled",
ACPI will not try to change the brightness level any more.

Either X will take charge of this or users can change the brightness level
by poking /sys/class/backlight/acpi_videoX/...

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index bd77e81e81c1..b1a56bf682ae 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -72,6 +72,9 @@ MODULE_AUTHOR("Bruno Ducrot");
 MODULE_DESCRIPTION("ACPI Video Driver");
 MODULE_LICENSE("GPL");
 
+static int brightness_switch_enabled = 1;
+module_param(brightness_switch_enabled, bool, 0644);
+
 static int acpi_video_bus_add(struct acpi_device *device);
 static int acpi_video_bus_remove(struct acpi_device *device, int type);
 
@@ -1850,27 +1853,32 @@ static void acpi_video_device_notify(acpi_handle handle, u32 event, void *data)
 
         switch (event) {
         case ACPI_VIDEO_NOTIFY_CYCLE_BRIGHTNESS:        /* Cycle brightness */
-                acpi_video_switch_brightness(video_device, event);
+                if (brightness_switch_enabled)
+                        acpi_video_switch_brightness(video_device, event);
                 acpi_bus_generate_proc_event(device, event, 0);
                 keycode = KEY_BRIGHTNESS_CYCLE;
                 break;
         case ACPI_VIDEO_NOTIFY_INC_BRIGHTNESS:  /* Increase brightness */
-                acpi_video_switch_brightness(video_device, event);
+                if (brightness_switch_enabled)
+                        acpi_video_switch_brightness(video_device, event);
                 acpi_bus_generate_proc_event(device, event, 0);
                 keycode = KEY_BRIGHTNESSUP;
                 break;
         case ACPI_VIDEO_NOTIFY_DEC_BRIGHTNESS:  /* Decrease brightness */
-                acpi_video_switch_brightness(video_device, event);
+                if (brightness_switch_enabled)
+                        acpi_video_switch_brightness(video_device, event);
                 acpi_bus_generate_proc_event(device, event, 0);
                 keycode = KEY_BRIGHTNESSDOWN;
                 break;
         case ACPI_VIDEO_NOTIFY_ZERO_BRIGHTNESS: /* zero brightnesss */
-                acpi_video_switch_brightness(video_device, event);
+                if (brightness_switch_enabled)
+                        acpi_video_switch_brightness(video_device, event);
                 acpi_bus_generate_proc_event(device, event, 0);
                 keycode = KEY_BRIGHTNESS_ZERO;
                 break;
         case ACPI_VIDEO_NOTIFY_DISPLAY_OFF:     /* display device off */
-                acpi_video_switch_brightness(video_device, event);
+                if (brightness_switch_enabled)
+                        acpi_video_switch_brightness(video_device, event);
                 acpi_bus_generate_proc_event(device, event, 0);
                 keycode = KEY_DISPLAY_OFF;
                 break;