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backlight: pwm_bl: Fix overflow condition

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[ Upstream commit 5d0c49aceb ]

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>
This commit is contained in:
Derek Basehore 2017-08-29 13:34:34 -07:00 committed by Greg Kroah-Hartman
parent d14718c9f4
commit 291c7e488f
1 changed files with 5 additions and 2 deletions
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7
drivers/video/backlight/pwm_bl.c
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@ -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)