From: Jason Stubbs <jasonbstubbs@gmail.com>
Subject: [PATCH] platform: fix samsung brightness min/max calculations

For one of the SABI configs, the valid brightness levels are 1 through 8 with
0 being reserved for the BIOS. To make the range 0-based, the driver is meant
to offset values to/from userspace by 1 giving valid levels of 0 through 7.

Currently, the driver is reporting a max brightness of 8 and doing the offset
the wrong way such that setting a brightness of 8 will set as 7 in hardware
while setting a brightness of 0 will attempt (and fail) to set as -1 in
hardware.

This patch fixes these calculations as well as a potential miscalculation due
to an assumption of min_brightness being either 0 or 1.

Signed-off-by: Jason Stubbs <jasonbstubbs@gmail.com>
Signed-off-by: Chuck Ebbert <cebbert@redhat.com>

---
Originally posted here, context fixed to apply to 3.0/3.1:
[ https://lkml.org/lkml/2011/5/11/548 ]

diff a/drivers/platform/x86/samsung-laptop.c b/drivers/platform/x86/samsung-laptop.c
--- 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);
 }
@@ -802,7 +804,8 @@ 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);
_