From: Mika Westerberg Date: Fri, 10 Jun 2016 12:43:21 +0000 (+0300) Subject: pwm: lpss: Prevent on_time_div overflow on lower frequencies X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=ab248b603960a4b6effaa9e16fc1ea84a33210c7;p=deliverable%2Flinux.git pwm: lpss: Prevent on_time_div overflow on lower frequencies If duty_ns is large enough multiplying it by 255 overflows and results wrong duty cycle value being programmed. For example with 10ms duty when period is 20ms (50%) we get 255 * 10000000 / 20000000 = -87 because 255 * 10000000 overlows int. Whereas correct value should be 255 * 10000000 / 20000000 = 127 Fix this by using unsigned long long as type for on_time_div and changing integer literals to use proper type annotation. Signed-off-by: Mika Westerberg Signed-off-by: Thierry Reding --- diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c index 98dc8b80b79d..be4658b42882 100644 --- a/drivers/pwm/pwm-lpss.c +++ b/drivers/pwm/pwm-lpss.c @@ -91,7 +91,7 @@ static int pwm_lpss_config(struct pwm_chip *chip, struct pwm_device *pwm, int duty_ns, int period_ns) { struct pwm_lpss_chip *lpwm = to_lpwm(chip); - u8 on_time_div; + unsigned long long on_time_div; unsigned long c, base_unit_range; unsigned long long base_unit, freq = NSEC_PER_SEC; u32 ctrl; @@ -113,7 +113,9 @@ static int pwm_lpss_config(struct pwm_chip *chip, struct pwm_device *pwm, if (duty_ns <= 0) duty_ns = 1; - on_time_div = 255 - (255 * duty_ns / period_ns); + on_time_div = 255ULL * duty_ns; + do_div(on_time_div, period_ns); + on_time_div = 255ULL - on_time_div; pm_runtime_get_sync(chip->dev);