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Commit 11fc4edc authored by Sean Young's avatar Sean Young Committed by Thierry Reding
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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: default avatarAndreas Christ <andreas@christ-faesch.ch>
Signed-off-by: default avatarSean Young <sean@mess.org>
Acked-by: default avatarStefan Wahren <wahrenst@gmx.net>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 3f467ebe

drivers/pwm/pwm-bcm2835.c

+5 −3
Original line number Diff line number Diff line
@@ -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;

}