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Commit 7341c785 authored by Martin Blumenstingl's avatar Martin Blumenstingl Committed by Thierry Reding
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pwm: meson: Add support PWM_POLARITY_INVERSED when disabling 



meson_pwm_apply() has to consider the PWM polarity when disabling the
output.
With enabled=false and polarity=PWM_POLARITY_NORMAL the output needs to
be LOW. The driver already supports this.
With enabled=false and polarity=PWM_POLARITY_INVERSED the output needs
to be HIGH. Implement this in the driver by internally enabling the
output with the same settings that we already use for "period == duty".

This fixes a PWM API violation which expects that the driver honors the
polarity also for enabled=false. Due to the IP block not supporting this
natively we only get "an as close as possible" to 100% HIGH signal (in
my test setup with input clock of 24MHz and measuring the output with a
logic analyzer at 24MHz sampling rate I got a duty cycle of 99.998475%
on a Khadas VIM).

Reviewed-by: default avatarNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: default avatarMartin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent d6885b3e

drivers/pwm/pwm-meson.c

+22 −1
Original line number Diff line number Diff line
@@ -245,6 +245,7 @@ static void meson_pwm_disable(struct meson_pwm *meson, struct pwm_device *pwm) 
static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,

			   struct pwm_state *state)

{

	struct meson_pwm_channel *channel = pwm_get_chip_data(pwm);

	struct meson_pwm *meson = to_meson_pwm(chip);

	int err = 0;
@@ -252,7 +253,27 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, 
		return -EINVAL;



	if (!state->enabled) {

		if (state->polarity == PWM_POLARITY_INVERSED) {

			/*

			 * This IP block revision doesn't have an "always high"

			 * setting which we can use for "inverted disabled".

			 * Instead we achieve this using the same settings

			 * that we use a pre_div of 0 (to get the shortest

			 * possible duration for one "count") and

			 * "period == duty_cycle". This results in a signal

			 * which is LOW for one "count", while being HIGH for

			 * the rest of the (so the signal is HIGH for slightly

			 * less than 100% of the period, but this is the best

			 * we can achieve).

			 */

			channel->pre_div = 0;

			channel->hi = ~0;

			channel->lo = 0;



			meson_pwm_enable(meson, pwm);

		} else {

			meson_pwm_disable(meson, pwm);

		}

	} else {

		err = meson_pwm_calc(meson, pwm, state);

		if (err < 0)