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

    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>
    ---
    diff --git a/drivers/platform/x86/samsung-laptop.c b/drivers/platform/x86/samsung-laptop.c
    index 01d5278..995b041 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;

    if (user_level == read_brightness()) {
    return;
    @@ -799,7 +801,8 @@ 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);

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