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SubjectRe: [PATCH] pwm: mediatek: support inverted polarity
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

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 (/* ... */)

> + 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/ |
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