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Commit 684309e5 authored by Andy Shevchenko's avatar Andy Shevchenko Committed by Thierry Reding
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pwm: lpss: Avoid potential overflow of base_unit 



The resolution of base_unit is derived from base_unit_bits and thus must be
equal to (2^base_unit_bits - 1). Otherwise frequency and therefore base_unit
might potentially overflow.

Prevent the above by substracting 1 in all cases where base_unit_bits or
derivative is used.

Reviewed-by: default avatarMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 8d254a34

drivers/pwm/pwm-lpss.c

+3 −3
Original line number Diff line number Diff line
@@ -102,7 +102,7 @@ static int pwm_lpss_config(struct pwm_chip *chip, struct pwm_device *pwm, 
	 * The equation is:

	 * base_unit = round(base_unit_range * freq / c)

	 */

	base_unit_range = BIT(lpwm->info->base_unit_bits);

	base_unit_range = BIT(lpwm->info->base_unit_bits) - 1;

	freq *= base_unit_range;



	base_unit = DIV_ROUND_CLOSEST_ULL(freq, c);
@@ -117,8 +117,8 @@ static int pwm_lpss_config(struct pwm_chip *chip, struct pwm_device *pwm, 


	ctrl = pwm_lpss_read(pwm);

	ctrl &= ~PWM_ON_TIME_DIV_MASK;

	ctrl &= ~((base_unit_range - 1) << PWM_BASE_UNIT_SHIFT);

	base_unit &= (base_unit_range - 1);

	ctrl &= ~(base_unit_range << PWM_BASE_UNIT_SHIFT);

	base_unit &= base_unit_range;

	ctrl |= (u32) base_unit << PWM_BASE_UNIT_SHIFT;

	ctrl |= on_time_div;

	pwm_lpss_write(pwm, ctrl);