From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Song Chen <chensong_2000@189.cn>
Cc: johan@kernel.org, elder@kernel.org, gregkh@linuxfoundation.org,
thierry.reding@gmail.com, lee.jones@linaro.org,
greybus-dev@lists.linaro.org, linux-staging@lists.linux.dev,
linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org
Subject: Re: [PATCH] staging: greybus: introduce pwm_ops::apply
Date: Fri, 11 Feb 2022 08:16:01 +0100 [thread overview]
Message-ID: <20220211071601.4rpfbkit6c6dre2o@pengutronix.de> (raw)
In-Reply-To: <6acc4f74-31a1-75b2-f7e8-610aac7b0ec8@189.cn>
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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@189.cn>
> > > ---
> > > 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@pengutronix.de/
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.
> 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
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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next prev parent reply other threads:[~2022-02-11 7:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-10 9:05 [PATCH] staging: greybus: introduce pwm_ops::apply Song Chen
2022-02-10 10:03 ` Uwe Kleine-König
2022-02-11 3:06 ` Song Chen
2022-02-11 7:16 ` Uwe Kleine-König [this message]
2022-02-11 7:48 ` Song Chen
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