From: Nylon Chen <nylon.chen@sifive.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: aou@eecs.berkeley.edu, conor@kernel.org,
emil.renner.berthing@canonical.com, geert+renesas@glider.be,
heiko@sntech.de, krzysztof.kozlowski+dt@linaro.org,
palmer@dabbelt.com, paul.walmsley@sifive.com, robh+dt@kernel.org,
thierry.reding@gmail.com, devicetree@vger.kernel.org,
linux-pwm@vger.kernel.org, linux-riscv@lists.infradead.org,
linux-kernel@vger.kernel.org, nylon7717@gmail.com,
zong.li@sifive.com, greentime.hu@sifive.com
Subject: Re: [PATCH v2 2/2] pwm: sifive: change the PWM controlled LED algorithm
Date: Tue, 21 Feb 2023 13:54:29 +0800 [thread overview]
Message-ID: <CAHh=Yk-ejA5W=G2Z7L3pVZzUt6DCF+6moJSc4rg0OQWO2fLXZg@mail.gmail.com> (raw)
In-Reply-To: <CAHh=Yk85NHbm9eUKLm75GUP4gSP5eYFjVabTUXseyB6wHD4D=Q@mail.gmail.com>
Hi Uwe,
Nylon Chen <nylon.chen@sifive.com> 於 2023年2月3日 週五 下午4:06寫道:
>
> Hi Uwe,
>
> Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 於 2023年1月30日 週一 下午6:17寫道:
> >
> > On Mon, Jan 30, 2023 at 05:32:29PM +0800, Nylon Chen wrote:
> > > The `frac` variable represents the pulse inactive time, and the result of
> > > this algorithm is the pulse active time. Therefore, we must reverse the
> > > result.
> > >
> > > The reference is SiFive FU740-C000 Manual[0].
> > >
> > > [0]: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf
> > >
> > > Signed-off-by: Nylon Chen <nylon.chen@sifive.com>
> > > ---
> > > drivers/pwm/pwm-sifive.c | 1 +
> > > 1 file changed, 1 insertion(+)
> > >
> > > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> > > index 62b6acc6373d..a5eda165d071 100644
> > > --- a/drivers/pwm/pwm-sifive.c
> > > +++ b/drivers/pwm/pwm-sifive.c
> > > @@ -158,6 +158,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > > frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
> > > /* The hardware cannot generate a 100% duty cycle */
> > > frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
> > > + frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
> >
> > The same problem exists in pwm_sifive_get_state(), doesn't it?
> >
> > As fixing this is an interruptive change anyhow, this is the opportunity
> > to align the driver to the rules tested by PWM_DEBUG.
> >
> > The problems I see in the driver (only checked quickly, so I might be
> > wrong):
> >
>
> > - state->period != ddata->approx_period isn't necessarily a problem. If
> > state->period > ddata->real_period that's fine and the driver should
> > continue
> >
> > - frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
> > is wrong for two reasons:
> > it should round down and use the real period.
I have some results from my observations regarding the questions you raised.
I don't know if what we are thinking is the same thing.
If my assumptions are different from yours, please let me know. Thanks.
> are you mean state->period is a redundancy variable so we can use
> ddata->real_period directly?
>
> it seems reasonable, but I don't get your point, why do we need to
> change the algorithm to DIV_ROUND_DOWN_ULL() and change the if-else
> condition.
>
> frac = DIV_ROUND_DOWN_ULL(num, ddata->real_period);
> if (state->period < ddata->approx_period) {
> ...
> }
>
> >
> > Best regards
> > Uwe
> >
> > --
> > Pengutronix e.K. | Uwe Kleine-König |
> > Industrial Linux Solutions | https://www.pengutronix.de/ |
next prev parent reply other threads:[~2023-02-21 5:54 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-30 9:32 [PATCH v2 0/2] Change PWM-controlled LED pin active mode and algorithm Nylon Chen
2023-01-30 9:32 ` [PATCH v2 1/2] riscv: dts: sifive: unleashed/unmatched: Remove PWM controlled LED's active-low properties Nylon Chen
2023-01-31 18:31 ` Conor Dooley
2023-02-01 8:59 ` Nylon Chen
2023-01-30 9:32 ` [PATCH v2 2/2] pwm: sifive: change the PWM controlled LED algorithm Nylon Chen
2023-01-30 9:53 ` Geert Uytterhoeven
2023-02-01 8:51 ` Nylon Chen
2023-01-30 10:17 ` Uwe Kleine-König
2023-02-01 8:56 ` Nylon Chen
2023-03-01 9:20 ` Uwe Kleine-König
2023-03-02 10:41 ` Nylon Chen
2023-02-03 8:06 ` Nylon Chen
2023-02-21 5:54 ` Nylon Chen [this message]
2023-09-08 10:41 ` Nylon Chen
2023-09-08 14:49 ` Uwe Kleine-König
2023-09-10 13:16 ` Nylon Chen
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