From 11fc4edc483bea8bf0efa0cc726886d2342f6fa6 Mon Sep 17 00:00:00 2001 From: Sean Young Date: Mon, 3 Jun 2019 10:00:58 +0100 Subject: [PATCH] pwm: bcm2835: Improve precision of PWM If sending IR with carrier of 455kHz using the pwm-ir-tx driver, the carrier ends up being 476kHz. The clock is set to bcm2835-pwm with a rate of 10MHz. A carrier of 455kHz has a period of 2198ns, but the arithmetic truncates this to 2100ns rather than 2200ns. So, use DIV_ROUND_CLOSEST() to reduce rounding errors, and we have a much more accurate carrier of 454.5kHz. Reported-by: Andreas Christ Signed-off-by: Sean Young Acked-by: Stefan Wahren Signed-off-by: Thierry Reding --- drivers/pwm/pwm-bcm2835.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c index 5652f461d994..f6fe0b922e1e 100644 --- a/drivers/pwm/pwm-bcm2835.c +++ b/drivers/pwm/pwm-bcm2835.c @@ -70,7 +70,7 @@ static int bcm2835_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, return -EINVAL; } - scaler = NSEC_PER_SEC / rate; + scaler = DIV_ROUND_CLOSEST(NSEC_PER_SEC, rate); if (period_ns <= MIN_PERIOD) { dev_err(pc->dev, "period %d not supported, minimum %d\n", @@ -78,8 +78,10 @@ static int bcm2835_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, return -EINVAL; } - writel(duty_ns / scaler, pc->base + DUTY(pwm->hwpwm)); - writel(period_ns / scaler, pc->base + PERIOD(pwm->hwpwm)); + writel(DIV_ROUND_CLOSEST(duty_ns, scaler), + pc->base + DUTY(pwm->hwpwm)); + writel(DIV_ROUND_CLOSEST(period_ns, scaler), + pc->base + PERIOD(pwm->hwpwm)); return 0; }