[PATCH AUTOSEL for 3.18 27/40] backlight: pwm_bl: Fix overflow condition

[alexander . levin]

From: Derek Basehore <dbaseh...@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 <dbaseh...@chromium.org>
Acked-by: Thierry Reding <thierry.red...@gmail.com>
Reviewed-by: Brian Norris <briannor...@chromium.org>
Signed-off-by: Lee Jones <lee.jo...@linaro.org>
Signed-off-by: Sasha Levin <alexander.le...@verizon.com>
---
 drivers/video/backlight/pwm_bl.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index cb5ae4c08469..3610e2ff5763 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -78,14 +78,17 @@ 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)
-- 
2.11.0