diff options
| author |   Sean Young <sean@mess.org> | 2019-06-03 10:00:58 +0100 |
|---|---|---|
| committer |   Thierry Reding <thierry.reding@gmail.com> | 2019-06-26 11:39:12 +0200 |
| commit | 11fc4edc483bea8bf0efa0cc726886d2342f6fa6 (patch) | |
| tree | 19f3bdfc1f4cc7971343688f35770b629c28b5c9 /drivers/pwm | |
| parent | leds: pwm: Support ACPI via firmware-node framework (diff) | |
| download | linux-dev-11fc4edc483bea8bf0efa0cc726886d2342f6fa6.tar.xz linux-dev-11fc4edc483bea8bf0efa0cc726886d2342f6fa6.zip | |
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 <andreas@christ-faesch.ch>
Signed-off-by: Sean Young <sean@mess.org>
Acked-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm')
| -rw-r--r-- | drivers/pwm/pwm-bcm2835.c | 8 |
1 files 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; } |