diff options
| -rw-r--r-- | drivers/pwm/pwm-bcm2835.c | 35 |
1 files changed, 27 insertions, 8 deletions
diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c index 6ff5f04b3e07..d593cce249d9 100644 --- a/drivers/pwm/pwm-bcm2835.c +++ b/drivers/pwm/pwm-bcm2835.c @@ -64,8 +64,9 @@ static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, struct bcm2835_pwm *pc = to_bcm2835_pwm(chip); unsigned long rate = clk_get_rate(pc->clk); - unsigned long long period; - unsigned long scaler; + unsigned long long period_cycles; + u64 max_period; + u32 val; if (!rate) { @@ -73,18 +74,36 @@ static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, return -EINVAL; } - scaler = DIV_ROUND_CLOSEST(NSEC_PER_SEC, rate); + /* + * period_cycles must be a 32 bit value, so period * rate / NSEC_PER_SEC + * must be <= U32_MAX. As U32_MAX * NSEC_PER_SEC < U64_MAX the + * multiplication period * rate doesn't overflow. + * To calculate the maximal possible period that guarantees the + * above inequality: + * + * round(period * rate / NSEC_PER_SEC) <= U32_MAX + * <=> period * rate / NSEC_PER_SEC < U32_MAX + 0.5 + * <=> period * rate < (U32_MAX + 0.5) * NSEC_PER_SEC + * <=> period < ((U32_MAX + 0.5) * NSEC_PER_SEC) / rate + * <=> period < ((U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC/2) / rate + * <=> period <= ceil((U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC/2) / rate) - 1 + */ + max_period = DIV_ROUND_UP_ULL((u64)U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC / 2, rate) - 1; + + if (state->period > max_period) + return -EINVAL; + /* set period */ - period = DIV_ROUND_CLOSEST_ULL(state->period, scaler); + period_cycles = DIV_ROUND_CLOSEST_ULL(state->period * rate, NSEC_PER_SEC); - /* dont accept a period that is too small or has been truncated */ - if ((period < PERIOD_MIN) || (period > U32_MAX)) + /* don't accept a period that is too small */ + if (period_cycles < PERIOD_MIN) return -EINVAL; - writel(period, pc->base + PERIOD(pwm->hwpwm)); + writel(period_cycles, pc->base + PERIOD(pwm->hwpwm)); /* set duty cycle */ - val = DIV_ROUND_CLOSEST_ULL(state->duty_cycle, scaler); + val = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * rate, NSEC_PER_SEC); writel(val, pc->base + DUTY(pwm->hwpwm)); /* set polarity */ |