platform: samsung_laptop: fix samsung brightness min/max calculations

The min_brightness value of the sabi_config is incorrectly used in brightness
calculations. For the config where min_brightness = 1 and max_brightness = 8,
the user visible range should be 0 to 7 with hardware being set in the range
of 1 to 8. What is actually happening is that the user visible range is 0 to
8 with hardware being set in the range of -1 to 7.

This patch fixes the above issue as well as a miscalculation that would occur
in the case of min_brightness > 1.

Signed-off-by: Jason Stubbs <jasonbstubbs@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/platform/x86/samsung-laptop.c b/drivers/platform/x86/samsung-laptop.c
index 37374a5878eb..7eb6733138e6 100644
--- a/drivers/platform/x86/samsung-laptop.c
+++ b/drivers/platform/x86/samsung-laptop.c
@@ -370,15 +370,17 @@ static u8 read_brightness(void)
                                   &sretval);
         if (!retval) {
                 user_brightness = sretval.retval[0];
-                if (user_brightness != 0)
+                if (user_brightness > sabi_config->min_brightness)
                         user_brightness -= sabi_config->min_brightness;
+                else
+                        user_brightness = 0;
         }
         return user_brightness;
 }
 
 static void set_brightness(u8 user_brightness)
 {
-        u8 user_level = user_brightness - sabi_config->min_brightness;
+        u8 user_level = user_brightness + sabi_config->min_brightness;
 
         sabi_set_command(sabi_config->commands.set_brightness, user_level);
 }
@@ -811,7 +813,8 @@ static int __init samsung_init(void)
         /* create a backlight device to talk to this one */
         memset(&props, 0, sizeof(struct backlight_properties));
         props.type = BACKLIGHT_PLATFORM;
-        props.max_brightness = sabi_config->max_brightness;
+        props.max_brightness = sabi_config->max_brightness -
+                                sabi_config->min_brightness;
         backlight_device = backlight_device_register("samsung", &sdev->dev,
                                                      NULL, &backlight_ops,
                                                      &props);