Messages in this thread | | | Date | Wed, 30 Aug 2017 16:13:09 +0200 | From | Thierry Reding <> | Subject | Re: [PATCH] pwm_bl: Fix overflow condition |
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On Tue, Aug 29, 2017 at 11:45:43AM -0700, dbasehore . wrote: > On Tue, Aug 29, 2017 at 7:05 AM, Thierry Reding > <thierry.reding@gmail.com> wrote: > > On Mon, Aug 28, 2017 at 01:00:33PM -0700, Derek Basehore wrote: > >> This fixes and overflow condition that happens with a high value of > >> brightness-levels-scale by using a 64-bit variable. The issue would > >> prevent a range of higher brightness levels from being set. > >> > >> Signed-off-by: Derek Basehore <dbasehore@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..e7ffd2108acf 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; > >> + s64 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; > >> } > > > > I don't think your commit message accurately describes the change here. > > The overflow that you're preventing might happen with a large value of > > pb->period (or rather, in combination with a large value of duty_cycle) > > but it's unrelated to pb->scale. > > I'm referring to the of property brightness-levels-scale.
I don't see a brightness-levels-scale property in either the DT bindings or the pwm-backlight driver. Do you have any pointers?
Thierry [unhandled content-type:application/pgp-signature] | |