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Commit ab248b60 authored by Mika Westerberg's avatar Mika Westerberg Committed by Thierry Reding
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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: default avatarMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent e5ca4245

drivers/pwm/pwm-lpss.c

+4 −2
Original line number Diff line number Diff line
@@ -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);