pwm_bl: Fix overflow condition
Subsystems (3)
PATCH v2 1/1 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.
--- drivers/video/backlight/pwm_bl.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
drivers/video/backlight/pwm_bl.c +5 -2
@@ -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)
Signature · 1 line
2.14.1.342.g6490525c54-goog
Quoted 6 lines · Derek Basehore
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]>---
I believe this is the correct v2 patch, and I agree that Derek is confused by his mail client :)
Quoted 30 lines
drivers/video/backlight/pwm_bl.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)drivers/video/backlight/pwm_bl.c +5
-2@@ -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)Signature · 1 line
2.14.1.342.g6490525c54-goog
Quoted 8 lines · Derek Basehore
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(-)
I'm still confused by the brightness-levels-scale comment in the other thread, but this looks like a good fix for a potential overflow so:
Quoted 2 lines · Thierry Reding
I'm still confused by the brightness-levels-scale comment in the other thread,
I believe Derek was accidentally referring to a change that's only in our downstream tree.
Quoted 1 line
but this looks like a good fix for a potential overflow so:
Right, it's still an applicable overflow without our downstream changes.
Brian
Quoted 1 line
Acked-by Thierry Reding <[email protected]>
Quoted 8 lines · Derek Basehore
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(-)
Applied for v4.15, thanks.
Signature · 4 lines
Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog