Messages in this thread | | | Subject | Re: [PATCH 13/14] pwm: meson: add support PWM_POLARITY_INVERSED when disabling | From | Neil Armstrong <> | Date | Mon, 27 May 2019 14:33:42 +0200 |
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On 25/05/2019 20:11, Martin Blumenstingl wrote: > 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). > > Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> > --- > drivers/pwm/pwm-meson.c | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-) > > diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c > index 900d362ec3c9..bb48ba85f756 100644 > --- a/drivers/pwm/pwm-meson.c > +++ b/drivers/pwm/pwm-meson.c > @@ -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) >
While not perfect, it almost fills the gap. Another way would be to use a specific pinctrl state setting the pin in GPIO output in high level, but this implementation could stay if the pinctrl state isn't available.
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
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