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pwm: meson: Add support PWM_POLARITY_INVERSED when disabling

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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: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
This commit is contained in:
Martin Blumenstingl 2019-06-12 21:59:10 +02:00 committed by Thierry Reding
parent d6885b3e0a
commit 7341c785d8
1 changed files with 22 additions and 1 deletions
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23
drivers/pwm/pwm-meson.c
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@ -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) {
meson_pwm_disable(meson, pwm);
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)