backlight: pwm_bl: Fix overflow condition

[ 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>

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 9bd1768..1c2289d 100644 (file)
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -79,14 +79,17 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
 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)