Messages in this thread | | | Date | Fri, 03 Mar 2023 23:23:07 +0100 | From | Lorenz Brun <> | Subject | Re: [PATCH] pwm: mediatek: support inverted polarity |
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On Fri, Mar 3 2023 at 22:17:25 +01:00:00, Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote: > On Fri, Mar 03, 2023 at 09:58:21PM +0100, Lorenz Brun wrote: >> According to the MT7986 Reference Manual the Mediatek PWM >> controller >> doesn't appear to have support for inverted polarity. >> >> This implements the same solution as in pwm-meson and just inverts >> the >> duty cycle instead, which results in the same outcome. > > This idea is broken. This was recently discussed on the linux-pwm list > and I hope will be fixed soon. See > https://lore.kernel.org/linux-pwm/20230228093911.bh2sbp4tyfir2z5g@pengutronix.de/T/#meda75ffbd4ef2048991ea2cd091c0c14b1bb09c2 > Is the issue here emulating PWM_POLARITY_INVERSED by inverting the period or the overflow issues? This driver currently rejects PWM_POLARITY_INVERSED, but the problem is that I have a board which inverts the output of the PWM peripheral (low-side MOSFET for higher-voltage open-drain output), thus I need to set the PWM node to output an inverted signal so that the final open-drain output behaves correctly as the signal has been inverted twice now.
In my specific case this logic could also be added to pwm-fan, but this would lead to more complexity there as this type of circuit is generally handled by the PWM driver.
> So this patch won't be accepted, still pointing out a style problem > below. > >> Signed-off-by: Lorenz Brun <lorenz@brun.one> >> --- >> drivers/pwm/pwm-mediatek.c | 13 +++++++++---- >> 1 file changed, 9 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c >> index 5b5eeaff35da..6f4a54c8299f 100644 >> --- a/drivers/pwm/pwm-mediatek.c >> +++ b/drivers/pwm/pwm-mediatek.c >> @@ -202,9 +202,7 @@ static int pwm_mediatek_apply(struct pwm_chip >> *chip, struct pwm_device *pwm, >> const struct pwm_state *state) >> { >> int err; >> - >> - if (state->polarity != PWM_POLARITY_NORMAL) >> - return -EINVAL; >> + u64 duty_cycle; >> >> if (!state->enabled) { >> if (pwm->state.enabled) >> @@ -213,7 +211,14 @@ static int pwm_mediatek_apply(struct pwm_chip >> *chip, struct pwm_device *pwm, >> return 0; >> } >> >> - err = pwm_mediatek_config(pwm->chip, pwm, state->duty_cycle, >> state->period); >> + // According to the MT7986 Reference Manual the peripheral does >> not >> + // appear to have the capability to invert the output. Instead >> just >> + // invert the duty cycle. > > Wrong commenting style, please stick to C-style comments (/* ... */) I can fix that if I end up submitting a V2 of this patch, but this didn't get picked up by checkpatch.
> >> + duty_cycle = state->duty_cycle; >> + if (state->polarity == PWM_POLARITY_INVERSED) >> + duty_cycle = state->period - state->duty_cycle; >> + >> + err = pwm_mediatek_config(pwm->chip, pwm, duty_cycle, >> state->period); >> if (err) >> return err; > > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König > | > Industrial Linux Solutions | > https://www.pengutronix.de/ |
Regards, Lorenz
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