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    Subject[PATCH 4.14 101/159] backlight: pwm_bl: Fix overflow condition
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Derek Basehore <dbasehore@chromium.org>


    [ Upstream commit 5d0c49acebc9488e37db95f1d4a55644e545ffe7 ]

    This fixes an overflow condition that can happen with high max
    brightness and period values in compute_duty_cycle. This fixes it by
    using a 64 bit variable for computing the duty cycle.

    Signed-off-by: Derek Basehore <dbasehore@chromium.org>
    Acked-by: Thierry Reding <thierry.reding@gmail.com>
    Reviewed-by: Brian Norris <briannorris@chromium.org>
    Signed-off-by: Lee Jones <lee.jones@linaro.org>
    Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/video/backlight/pwm_bl.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    --- a/drivers/video/backlight/pwm_bl.c
    +++ b/drivers/video/backlight/pwm_bl.c
    @@ -79,14 +79,17 @@ static void pwm_backlight_power_off(stru
    static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
    {
    unsigned int lth = pb->lth_brightness;
    - int duty_cycle;
    + u64 duty_cycle;

    if (pb->levels)
    duty_cycle = pb->levels[brightness];
    else
    duty_cycle = brightness;

    - return (duty_cycle * (pb->period - lth) / pb->scale) + lth;
    + duty_cycle *= pb->period - lth;
    + do_div(duty_cycle, pb->scale);
    +
    + return duty_cycle + lth;
    }

    static int pwm_backlight_update_status(struct backlight_device *bl)

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