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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: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
This commit is contained in:
Andy Shevchenko 2017-01-28 17:10:39 +02:00 committed by Thierry Reding
parent 8d254a340e
commit 684309e504
1 changed files with 3 additions and 3 deletions
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6
drivers/pwm/pwm-lpss.c
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@ -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);