Message-ID: <CAOX-t56F2u_1=tA4N4Wvicw-e9J4ksN__J70QZtjZwJRjgesUQ@mail.gmail.com>
Date:   Tue, 8 Mar 2022 20:03:55 +0800
From:   hammer hsieh <hammerh0314@...il.com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     thierry.reding@...il.com, lee.jones@...aro.org, robh+dt@...nel.org,
        linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, wells.lu@...plus.com,
        "hammer.hsieh" <hammer.hsieh@...plus.com>, kernel@...gutronix.de
Subject: Re: [PATCH v2 2/2] pwm:sunplus-pwm:Add Sunplus SoC PWM Driver

Uwe Kleine-König <u.kleine-koenig@...gutronix.de> 於 2022年3月7日 週一 下午9:10寫道：
>
> Hello,
>
> On Mon, Mar 07, 2022 at 08:50:10PM +0800, hammer hsieh wrote:
> > Uwe Kleine-König <u.kleine-koenig@...gutronix.de> 於 2022年3月5日 週六 上午2:57寫道：
> > > On Fri, Mar 04, 2022 at 02:20:12PM +0800, Hammer Hsieh wrote:
> > > > diff --git a/drivers/pwm/pwm-sunplus.c b/drivers/pwm/pwm-sunplus.c
> > > > new file mode 100644
> > > > index 0000000..170534f
> > > > --- /dev/null
> > > > +++ b/drivers/pwm/pwm-sunplus.c
> > > > @@ -0,0 +1,229 @@
> > > > +// SPDX-License-Identifier: GPL-2.0
> > > > +/*
> > > > + * PWM device driver for SUNPLUS SoCs
> > >
> > > Is there a public manual available for this hardware? If yes, please add
> > > a link here.
> >
> > yes, will add links as below
> > https://sunplus-tibbo.atlassian.net/wiki/spaces/doc/overview
> > https://sunplus.atlassian.net/wiki/spaces/doc/pages/461144198/12.+Pulse+Width+Modulation+PWM
> >
> > > > + *
> > > > + * Limitations:
> > > > + * - Only supports normal polarity.
> > >
> > > How does the HW behave when it's disabled? Usual candidates are:
> > >  - It freezes at where it currently is
> > >  - It outputs low
> > >  - It becomes tristate
> > >
> > > Please note this in the Limitations section, too.
> > >
> > > Another thing to mention is if running periods are completed when the
> > > parameters change.
> > >
> >
> > ok, will add note as below
> >   Limitations:
> >   - Only supports normal polarity.
> >   - It output low when PWM channel disabled.
> >   - When the parameters change, current running period will not be completed
> >       and run new settings immediately.
>
> Sounds good.
>
> Other thing that might maybe happen: in .apply() you write the register
> for period first and then the one for duty_cycle. Can it happen, that
> for a moment the output is defined by new period and old duty_cycle?
> That would be another thing to note.
>

ok, i will add note for it.
  - In .apply() PWM output need to write register FREQ and DUTY. When
first write FREQ
      done and not yet write DUTY, it has short timing gap use new
FREQ and old DUTY.

> > > > +struct sunplus_pwm {
> > > > +     struct pwm_chip chip;
> > > > +     void __iomem *base;
> > > > +     struct clk *clk;
> > > > +     u32 approx_period[PWM_SUP_NUM];
> > > > +     u32 approx_duty_cycle[PWM_SUP_NUM];
> > > > +};
> > > > +
> > > > +static inline struct sunplus_pwm *to_sunplus_pwm(struct pwm_chip *chip)
> > > > +{
> > > > +     return container_of(chip, struct sunplus_pwm, chip);
> > > > +}
> > > > +
> > > > +static void sunplus_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> > > > +{
> > > > +     struct sunplus_pwm *priv = to_sunplus_pwm(chip);
> > > > +     u32 value;
> > > > +
> > > > +     /* disable pwm channel output */
> > > > +     value = readl(priv->base + PWM_SUP_CONTROL0);
> > > > +     value &= ~BIT(pwm->hwpwm);
> > > > +     writel(value, priv->base + PWM_SUP_CONTROL0);
> > > > +     /* disable pwm channel clk source */
> > > > +     value = readl(priv->base + PWM_SUP_CONTROL1);
> > > > +     value &= ~BIT(pwm->hwpwm);
> > > > +     writel(value, priv->base + PWM_SUP_CONTROL1);
> > >
> > > the .free callback isn't supposed to modify the hardware.
> >
> > But how to turn pwm channel off ?
> > I add .free function for turn it off.
> > In user space
> >   cd /sys/class/pwm/pwmchip0
> >   echo 0 > export
> >   cd pwm0
> >   echo 20000000 > period
> >   echo 1000000 > duty_cycle
> >   echo 1 > enable
> >   cd ..
> >   echo 0 > unexport ; turn off pwm will call .free function
>
> unexport should just keep the PWM configured as is. To turn it of, don't
> unexport but echo 0 > enable.
>

ok, i will remove .free function.

> > > > +     u32 tmp, rate;
> > > > +     u64 max_period, period_ns, duty_ns, clk_rate;
> > > > +
> > > > +     if (state->polarity != pwm->state.polarity)
> > > > +             return -EINVAL;
> > > > +
> > > > +     if (!state->enabled) {
> > > > +             /* disable pwm channel output */
> > > > +             value = readl(priv->base + PWM_SUP_CONTROL0);
> > > > +             value &= ~BIT(pwm->hwpwm);
> > >
> > > I'd give this one a name. Something like:
> > >
> > >         #define PWM_SUP_CONTROL_EN(ch)  BIT(ch)
> > >
> > > (Pick the right name from the manual.)
> >
> > That means it need to implement
> > PWM_SUP_CONTROL_EN(ch) and PWM_SUP_CONTROL_DIS(ch) ?
>
> PWM_SUP_CONTROL_EN(ch) should be enough, PWM_SUP_CONTROL_DIS(ch) would
> just be 0 which doens't make much sense.
>

ok , i will add #define PWM_SP7021_CONTROL_EN(ch) BIT(ch).
value &= ~BIT(pwm->hwpwm); should be change to
value &= ~PWM_SP7021_CONTROL_EN(pwm->hwpwm);

> >
> > > > +             writel(value, priv->base + PWM_SUP_CONTROL0);
> > > > +             /* disable pwm channel clk source */
> > > > +             value = readl(priv->base + PWM_SUP_CONTROL1);
> > > > +             value &= ~BIT(pwm->hwpwm);
> > > > +             writel(value, priv->base + PWM_SUP_CONTROL1);
> > > > +             return 0;
> > > > +     }
> > > > +
> > > > +     clk_rate = clk_get_rate(priv->clk);
> > > > +     rate = (u32)clk_rate / 100000;
> > >
> > > This cast doesn't change anything, does it?
> >
> > yes, clk_rate should be 202.5MHz, to prevent overflow use 2025 to calculate.
>
> I only talked about the cast, so
>
>         rate = clk_rate / 100000;
>
> should have the same effect and is a tad nicer.
>

since i use mul_u64_u64_div_u64(a,b,c)
max_period = mul_u64_u64_div_u64(PWM_SP7021_FREQ_MAX,
(u64)PWM_SP7021_FREQ_SCALER
  * NSEC_PER_SEC, clk_rate);
seems not necessary for "rate = clk_rate / 100000".

> > > > +     max_period = PWM_SUP_FREQ_MAX * (PWM_SUP_FREQ_SCALER * 10000 / rate);
> > >
> > > Here you have rounding issues. Consider rate = 3329. Then you get
> > > max_period = 0xffff * (2560000 / 3329) = 0xffff * 768 = 50330880.
> > >
> > > However the actual result is 50396395.31...
> > >
> > > Also dividing by the result of a division looses precision.
> > >
> >
> > I am not sure how to fix the rounding issue.(thinking...)
>
> the mul_u64_u64_div_u64 I suggested should be good.
>

it works.
 dd_freq = mul_u64_u64_div_u64(clk_rate, period_ns, (u64)PWM_SP7021_FREQ_SCALER
                 * NSEC_PER_SEC);

> > > > +     if (dd_freq == 0)
> > > > +             return -EINVAL;
> > > > +
> > > > +     if (dd_freq > PWM_SUP_FREQ_MAX)
> > > > +             dd_freq = PWM_SUP_FREQ_MAX;
> > > > +
> > > > +     writel(dd_freq, priv->base + PWM_SUP_FREQ(pwm->hwpwm));
> > > > +
> > > > +     /* cal and set pwm duty */
> > > > +     value = readl(priv->base + PWM_SUP_CONTROL0);
> > > > +     value |= BIT(pwm->hwpwm);
> > > > +     value1 = readl(priv->base + PWM_SUP_CONTROL1);
> > > > +     value1 |= BIT(pwm->hwpwm);
> > > > +     if (duty_ns == period_ns) {
> > > > +             value |= BIT(pwm->hwpwm + PWM_BYPASS_BIT_SHIFT);
> > > > +             duty = PWM_SUP_DUTY_MAX;
> > > > +     } else {
> > > > +             value &= ~BIT(pwm->hwpwm + PWM_BYPASS_BIT_SHIFT);
> > > > +             tmp = priv->approx_duty_cycle[pwm->hwpwm] * PWM_SUP_FREQ_SCALER;
> > > > +             tmp /= priv->approx_period[pwm->hwpwm];
> > >
> > > Please use the exact values available.
> >
> > The same reason, in case of enable PWM_DEBUG.
> > first call .apply , then it will call .get_state for verify the calculation.
>
> The overall goal is not to please PWM_DEBUG, but to use exact
> calculations and if you did that, PWM_DEBUG should be happy, too.
>

sure, will remove approx_xxxx code.

> > > > +             duty = (u32)tmp;
> > > > +             duty |= (pwm->hwpwm << PWM_DD_SEL_BIT_SHIFT);
> > > > +     }
> > > > +     writel(duty, priv->base + PWM_SUP_DUTY(pwm->hwpwm));
> > > > +     writel(value1, priv->base + PWM_SUP_CONTROL1);
> > > > +     writel(value, priv->base + PWM_SUP_CONTROL0);
> > >
> > > What is the difference between CONTROL1 and CONTROL0?
> >
> > PWM CONTROL0 for PWM channel switch.
> > PWM CONTROL1 for PWM clock source switch.
> > Actually PWM supports 8 channels , but clock source only 4 sets.
> > For easy control(now submit), I just support 4 PWM channels, and one
> > clock source for one pwm channel.
> > For complicated control(not now), 8 PWM channels 4 clock source , need
> > to manage clock source / pwm channel enable or not
> > while request/free pwm channel.
>
> So you can use (say) clk 2 to "drive" PWM channel 6? Where is that
> mapping defined. Only implementing 4 channels with a 1:1 mapping is ok,
> but you might want to ensure the mapping is indeed 1:1.
>

PWM CONTROL0 REG[7:0] for PWM channel on/off
PWM CONTROL1 REG[3:0] for PWM clock source on/off
PWM FREQ REG[15:0] freq = 1/clk_rate *256 * FREQ REG[15:0]
PWM DUTY REG[7:0] for duty,  REG[9:8] for clock source select.
  duty |= (pwm->hwpwm << PWM_DD_SEL_BIT_SHIFT); can make sure
clock source 0 for pwm0
clock source 1 for pwm1
clock source 2 for pwm2
clock source 3 for pwm3

> > > > +     return 0;
> > > > +}
> > > > +
> > > > +static void sunplus_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> > > > +                               struct pwm_state *state)
> > > > +{
> > > > +     struct sunplus_pwm *priv = to_sunplus_pwm(chip);
> > > > +     u32 value, freq, duty, rate, freq_tmp, duty_tmp;
> > > > +     u64 tmp, clk_rate;
> > > > +
> > > > +     value = readl(priv->base + PWM_SUP_CONTROL0);
> > > > +
> > > > +     if (value & BIT(pwm->hwpwm)) {
> > > > +             clk_rate = clk_get_rate(priv->clk);
> > > > +             rate = (u32)clk_rate / 100000;
> > > > +             freq = readl(priv->base + PWM_SUP_FREQ(pwm->hwpwm));
> > > > +             duty = readl(priv->base + PWM_SUP_DUTY(pwm->hwpwm));
> > > > +             duty &= ~GENMASK(9, 8);
> > > > +
> > > > +             freq_tmp = rate * priv->approx_period[pwm->hwpwm] / (PWM_SUP_FREQ_SCALER * 100);
> > > > +             duty_tmp = priv->approx_duty_cycle[pwm->hwpwm] * PWM_SUP_FREQ_SCALER /
> > > > +                             priv->approx_period[pwm->hwpwm];
> > > > +
> > > > +             if (freq == freq_tmp && duty == duty_tmp) {
> > > > +                     state->period = priv->approx_period[pwm->hwpwm] * 100;
> > > > +                     state->duty_cycle = priv->approx_duty_cycle[pwm->hwpwm] * 100;
> > > > +             } else {
> > > > +                     tmp = (u64)freq * PWM_SUP_FREQ_SCALER * 10000;
> > > > +                     state->period = div64_u64(tmp, rate);
> > > > +                     tmp = (u64)freq * (u64)duty * 10000;
> > > > +                     state->duty_cycle = div64_u64(tmp, rate);
> > > > +             }
> > > > +             state->enabled = true;
> > > > +     } else {
> > > > +             state->enabled = false;
> > > > +     }
> > > > +
> > > > +     state->polarity = PWM_POLARITY_NORMAL;
> > > > +}
> > >
> > > When .get_state() is first called, .apply wasn't called yet. Then
> > > priv->approx_period[pwm->hwpwm] is zero and the returned result is
> > > wrong. Please read the register values and calculate the implemented
> > > output without caching.
> >
> > The same reason, in case of enable PWM_DEBUG.
> > first call .apply , then it will call .get_state for verify the calculation.
> >
> > In get_state, I thought about that.
> > first called .get_state, read register value to calculate period and duty_cycle.
> > after calling .apply , caching data approx_period / approx_duty_cycle
> > will not zero.
> > then get_state will use caching data to do PWM_DEBUG self verification.
> > I will think about how to solve the PWM_DEBUG ".apply is not idempotent" issue.
>
> I'd say: Don't cache anything. In .get_state() just read the registers and
> determine .duty_cycle and .period from them, and in .apply() do the
> inverse.
>

got it.
i will modify code like below, and it works.
        state->period = mul_u64_u64_div_u64((u64)freq,
(u64)PWM_SP7021_FREQ_SCALER
                                        * NSEC_PER_SEC, clk_rate) + 1UL;
        state->duty_cycle = mul_u64_u64_div_u64((u64)freq, (u64)duty *
NSEC_PER_SEC,
                                        clk_rate) + 1UL;
seems like i need to plus 1 for it, or ".apply is not idempotent" will happen.

> > > > +     priv->clk = devm_clk_get_optional(dev, NULL);
> > > > +     if (IS_ERR(priv->clk))
> > , > > +             return dev_err_probe(dev, PTR_ERR(priv->clk),
> > > > +                                  "get pwm clock failed\n");
> > >
> > > If priv->clk is the dummy clk, clk_get_rate returns 0. This is bad as
> > > (at lease up to now) you divide by rate in .apply().
> > >
> >
> > I check many pwm drivers , they are called devm_clk_get_optional( ) or
> > devm_clk_get( ).
> > Could you tell me how to do it in a probe ?
>
> You can only sensibly use devm_clk_get_optional() if you don't rely on
> the rate of the clk. So the way to go here is to just use
> devm_clk_get().
>

ok, will modify it, change to devm_clk_get().

> > > > +     ret = devm_add_action_or_reset(dev,
> > > > +                                    (void(*)(void *))clk_disable_unprepare,
> > >
> > > Without checking my C book I'm unsure if this is save on all platforms.
> > > I'd implement a oneline function for this.
> >
> > ok, will implement it in one line.
> > static void sunplus_pwm_clk_release(*data)
> > {
> >    struct clk *clk = data;
> >    clk_disable_unprepare(clk);
> > }
> >  ret = devm_add_action_or_reset(dev, sunplus_pwm_clk_release, priv->clk);
> >
>
> *nod*
>
> > > > +                                    priv->clk);
> > > > +     if (ret)
> > >
> > > missing error message
> > >
> >
> > I didn't see another driver add an error message, is it necessary?
>
> IMHO yes. (Though the most likely error -ENOMEM, in this case no error
> message should be emitted.)
>

 ok, will add error message like below.
        if (ret < 0) {
                dev_err(dev, "failed to release clock: %d\n", ret);
                return ret;
        }
or should i modify like
        if (ret < 0) {
                dev_err(dev, "failed to release clock: %d\n", ret);
                return ERR_PTR(ret);
        }
i didn't find reference code for it, not sure which one is better?

thank you.

> Best regards
> Uwe
>
> --
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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