Commit ab248b60 authored Jun 10, 2016 by Mika Westerberg Committed by Thierry Reding Jul 11, 2016

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>

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);

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