Commit fe0aea79 authored by Jonathan Richardson's avatar Jonathan Richardson Committed by Thierry Reding
Browse files

pwm: kona: Modify settings application sequence 



Update the driver so that settings are applied in accordance with the
most recent version of the hardware spec.  The revised sequence clears
the trigger bit, waits 400ns, writes settings, sets the trigger bit,
and waits another 400ns.  This corrects an issue where occasionally a
requested change was not properly reflected in the PWM output.

Reviewed-by: default avatarArun Ramamurthy <arunrama@broadcom.com>
Reviewed-by: default avatarScott Branden <sbranden@broadcom.com>
Tested-by: default avatarScott Branden <sbranden@broadcom.com>
Reviewed-by: default avatarTim Kryger <tim.kryger@gmail.com>
Signed-off-by: default avatarJonathan Richardson <jonathar@broadcom.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 09c14459

drivers/pwm/pwm-bcm-kona.c

+38 −9
Original line number Diff line number Diff line
@@ -76,19 +76,36 @@ static inline struct kona_pwmc *to_kona_pwmc(struct pwm_chip *_chip) 
	return container_of(_chip, struct kona_pwmc, chip);

}



static void kona_pwmc_apply_settings(struct kona_pwmc *kp, unsigned int chan)

/*

 * Clear trigger bit but set smooth bit to maintain old output.

 */

static void kona_pwmc_prepare_for_settings(struct kona_pwmc *kp,

	unsigned int chan)

{

	unsigned int value = readl(kp->base + PWM_CONTROL_OFFSET);



	/* Clear trigger bit but set smooth bit to maintain old output */

	value |= 1 << PWM_CONTROL_SMOOTH_SHIFT(chan);

	value &= ~(1 << PWM_CONTROL_TRIGGER_SHIFT(chan));

	writel(value, kp->base + PWM_CONTROL_OFFSET);



	/*

	 * There must be a min 400ns delay between clearing trigger and setting

	 * it. Failing to do this may result in no PWM signal.

	 */

	ndelay(400);

}



static void kona_pwmc_apply_settings(struct kona_pwmc *kp, unsigned int chan)

{

	unsigned int value = readl(kp->base + PWM_CONTROL_OFFSET);



	/* Set trigger bit and clear smooth bit to apply new settings */

	value &= ~(1 << PWM_CONTROL_SMOOTH_SHIFT(chan));

	value |= 1 << PWM_CONTROL_TRIGGER_SHIFT(chan);

	writel(value, kp->base + PWM_CONTROL_OFFSET);



	/* Trigger bit must be held high for at least 400 ns. */

	ndelay(400);

}



static int kona_pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm,
@@ -133,8 +150,14 @@ static int kona_pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm, 
			return -EINVAL;

	}



	/* If the PWM channel is enabled, write the settings to the HW */

	/*

	 * Don't apply settings if disabled. The period and duty cycle are

	 * always calculated above to ensure the new values are

	 * validated immediately instead of on enable.

	 */

	if (pwm_is_enabled(pwm)) {

		kona_pwmc_prepare_for_settings(kp, chan);



		value = readl(kp->base + PRESCALE_OFFSET);

		value &= ~PRESCALE_MASK(chan);

		value |= prescale << PRESCALE_SHIFT(chan);
@@ -164,6 +187,8 @@ static int kona_pwmc_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, 
		return ret;

	}



	kona_pwmc_prepare_for_settings(kp, chan);



	value = readl(kp->base + PWM_CONTROL_OFFSET);



	if (polarity == PWM_POLARITY_NORMAL)
@@ -175,9 +200,6 @@ static int kona_pwmc_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, 


	kona_pwmc_apply_settings(kp, chan);



	/* Wait for waveform to settle before gating off the clock */

	ndelay(400);



	clk_disable_unprepare(kp->clk);



	return 0;
@@ -208,13 +230,20 @@ static void kona_pwmc_disable(struct pwm_chip *chip, struct pwm_device *pwm) 
{

	struct kona_pwmc *kp = to_kona_pwmc(chip);

	unsigned int chan = pwm->hwpwm;

	unsigned int value;



	kona_pwmc_prepare_for_settings(kp, chan);



	/* Simulate a disable by configuring for zero duty */

	writel(0, kp->base + DUTY_CYCLE_HIGH_OFFSET(chan));

	kona_pwmc_apply_settings(kp, chan);

	writel(0, kp->base + PERIOD_COUNT_OFFSET(chan));



	/* Wait for waveform to settle before gating off the clock */

	ndelay(400);

	/* Set prescale to 0 for this channel */

	value = readl(kp->base + PRESCALE_OFFSET);

	value &= ~PRESCALE_MASK(chan);

	writel(value, kp->base + PRESCALE_OFFSET);



	kona_pwmc_apply_settings(kp, chan);



	clk_disable_unprepare(kp->clk);

}

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