Re: [PATCH] staging: greybus: introduce pwm_ops::apply

[Song Chen]

Hello Uwe,

Thanks for the explain, now i can understand it better.

So, if redefining period and duty as u64 in gb_pwm_config_request is an 
acceptable solution, i will send patch v2.

BR

Song

在 2022/2/11 15:16, Uwe Kleine-König 写道:
> Hello ,
>
> On Fri, Feb 11, 2022 at 11:06:33AM +0800, Song Chen wrote:
> > 在 2022/2/10 18:03, Uwe Kleine-König 写道:
> > > On Thu, Feb 10, 2022 at 05:05:02PM +0800, Song Chen wrote:
> > > > Introduce apply in pwm_ops to replace legacy operations,
> > > > like enable, disable, config and set_polarity.
> > > >
> > > > Signed-off-by: Song Chen <chensong_2000@xxxxxx>
> > > > ---
> > > >    drivers/staging/greybus/pwm.c | 46 +++++++++++++++--------------------
> > > >    1 file changed, 19 insertions(+), 27 deletions(-)
> > > >
> > > > diff --git a/drivers/staging/greybus/pwm.c b/drivers/staging/greybus/pwm.c
> > > > index 891a6a672378..e1889cf979b2 100644
> > > > --- a/drivers/staging/greybus/pwm.c
> > > > +++ b/drivers/staging/greybus/pwm.c
> > > > @@ -204,43 +204,35 @@ static void gb_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> > > >    	gb_pwm_deactivate_operation(pwmc, pwm->hwpwm);
> > > >    }
> > > > -static int gb_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> > > > -			 int duty_ns, int period_ns)
> > > > -{
> > > > -	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> > > > -
> > > > -	return gb_pwm_config_operation(pwmc, pwm->hwpwm, duty_ns, period_ns);
> > > > -};
> > > > -
> > > > -static int gb_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
> > > > -			       enum pwm_polarity polarity)
> > > > +static int gb_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > > > +			const struct pwm_state *state)
> > > >    {
> > > > +	int ret;
> > > >    	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> > > > -	return gb_pwm_set_polarity_operation(pwmc, pwm->hwpwm, polarity);
> > > > -};
> > > > -
> > > > -static int gb_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> > > > -{
> > > > -	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> > > > +	/* set period and duty cycle*/
> > > > +	ret = gb_pwm_config_operation(pwmc, pwm->hwpwm, state->duty_cycle, state->period);
> > >
> > > gb_pwm_config_operation's 3rd parameter is an u32, so you're loosing
> > > bits here as state->duty_cycle is a u64. Ditto for period.
> >
> > originally, pwm_apply_state --> pwm_apply_legacy --> gb_pwm_config -->
> > gb_pwm_config_operation is also loosing bits, does it mean greybus can live
> > with that?
>
> This is true, I tried to address that, but Thierry had concerns.
> (https://lore.kernel.org/all/20210312212119.1342666-1-u.kleine-koenig@xxxxxxxxxxxxxx/
> was the patch I suggested.)
>
> > Or redefine gb_pwm_config_request, switch duty and period to __le64?
>
> Don't use __le64, this is only for representing (little endian) register
> values. u64 would be the right one.
>
> > > Also it would be nice if you go from
> > >
> > > 	.duty_cycle = A, .period = B, .enabled = 1
> > >
> > > to
> > >
> > > 	.duty_cycle = C, .period = D, .enabled = 0
> > >
> > > that C/D wasn't visible on the output pin. So please disable earlier
> > > (but keep enable at the end).
> >
> > sorry, i don't quite understand this part,
>
> To reexplain: If your hardware is configured for
>
> 	.duty_cycle = A, .period = B, .enabled = 1
>
> and pwm_apply is called with
>
> 	.duty_cycle = C, .period = D, .enabled = 0
>
> you configured the registers for .duty_cycle and .period first and only
> then disable the PWM. This usually results in glitches because the
> hardware shortly runs with
>
> 	.duty_cycle = C, .period = D, .enabled = 1
>
> . So the idea is, to disable before configuring duty and period if the
> eventual goal is a disabled state.

understood, thanks.

> > but is below code looking good to
> > you?
> >
> > static int gb_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > 			const struct pwm_state *state)
> > {
> > 	int err;
> > 	bool enabled = pwm->state.enabled;
> > 	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> >
> > 	/* set polarity */
> > 	if (state->polarity != pwm->state.polarity) {
> > 		if (enabled) {
> > 			gb_pwm_disable_operation(pwmc, pwm->hwpwm);
> > 			enabled = false;
> > 		}
> > 		err = gb_pwm_set_polarity_operation(pwmc, pwm->hwpwm, state->polarity);
> > 		if (err)
> > 			return err;
> > 	}
> >
> > 	if (!state->enabled) {
> > 		if (enabled)
> > 			gb_pwm_disable_operation(pwmc, pwm->hwpwm);
> > 		return 0;
> > 	}
> >
> > 	/* set period and duty cycle*/
> > 	err = gb_pwm_config_operation(pwmc, pwm->hwpwm, state->duty_cycle, state->period);
> > 	if (err)
> > 		return err;
> >
> > 	/* enable/disable */
> > 	if (!enabled)
> > 		return gb_pwm_enable_operation(pwmc, pwm->hwpwm);
> >
> > 	return 0;
> > }
>
> This looks good.
>
> Best regards
> Uwe