| Message ID | 20170829203434.6826-1-dbasehore@chromium.org |
|---|---|
| State | Deferred |
| Headers | show |
| Series | [v2] pwm_bl: Fix overflow condition | expand |
On Tue, Aug 29, 2017 at 01:34:34PM -0700, Derek Basehore wrote: > 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> > --- I believe this is the correct v2 patch, and I agree that Derek is confused by his mail client :) Reviewed-by: Brian Norris <briannorris@chromium.org> > 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Aug 29, 2017 at 01:34:34PM -0700, Derek Basehore wrote: > 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> > --- > 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: Acked-by: Thierry Reding <thierry.reding@gmail.com>
On Wed, Aug 30, 2017 at 04:27:41PM +0200, Thierry Reding wrote: > 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. > but this looks like a good fix for a potential overflow so: Right, it's still an applicable overflow without our downstream changes. Brian > Acked-by: Thierry Reding <thierry.reding@gmail.com> -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, 29 Aug 2017, Derek Basehore wrote: > 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> > --- > drivers/video/backlight/pwm_bl.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) Applied for v4.15, thanks.
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)
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> --- drivers/video/backlight/pwm_bl.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)