2017-08-29 20:27:56

by dbasehore .

Subject: [PATCH] pwm_bl: Fix overflow condition

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 <[email protected]>
---
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 76311ec5e400..5ccc8e34b7a6 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -88,14 +88,17 @@ 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)
--
2.14.1.342.g6490525c54-goog

2017-08-29 20:34:27

by dbasehore .

Subject: Re: [PATCH] pwm_bl: Fix overflow condition

Did not mean to send this in-reply to. It seems that git send-email
was not applying my "PATCH v2" prefix. Will resend as a separate
thread.