| Message ID | 20190525181133.4875-14-martin.blumenstingl@googlemail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | pwm-meson: cleanups and improvements | expand |
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>
Hi Neil, On Mon, May 27, 2019 at 2:33 PM Neil Armstrong <narmstrong@baylibre.com> wrote: > > 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. I just noticed that Amlogic updated the PWM IP block in G12A: it now supports "constant enable" (REG_MISC_AB bits 28 and 29) as well as PWM_POLARITY_INVERSED (REG_MISC_AB bits 26 and 27) natively! I like your idea of having a specific pinctrl state. we can implement that for anything older than G12A once we actually need it. for G12A we can do better thanks to the updated IP block Martin
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)
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(-)