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authorMika Westerberg <mika.westerberg@linux.intel.com>2016-06-10 15:43:21 +0300
committerThierry Reding <thierry.reding@gmail.com>2016-07-11 12:07:24 +0200
commitab248b603960a4b6effaa9e16fc1ea84a33210c7 (patch)
tree116a0ba4981a5e54960d934e0b5339809f089b99 /drivers/pwm
parente5ca42458b6278b7d5866e08dae7c45349af2157 (diff)
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 <mika.westerberg@linux.intel.com> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm')
-rw-r--r--drivers/pwm/pwm-lpss.c6
1 files changed, 4 insertions, 2 deletions
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);