From: Nylon Chen <nylon.chen@sifive.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: linux-riscv@lists.infradead.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org,
conor@kernel.org, robh+dt@kernel.org,
krzysztof.kozlowski+dt@linaro.org, palmer@dabbelt.com,
paul.walmsley@sifive.com, aou@eecs.berkeley.edu,
thierry.reding@gmail.com, vincent.chen@sifive.com,
zong.li@sifive.com, nylon7717@gmail.com
Subject: Re: [PATCH v8 2/3] pwm: sifive: change the PWM controlled LED algorithm
Date: Sat, 10 Feb 2024 11:09:05 +0800 [thread overview]
Message-ID: <CAHh=Yk8Zeuu7hyvF3f-27TOV+t1Pn3OpSFSQErV7maE1WQ6cqw@mail.gmail.com> (raw)
In-Reply-To: <4kqkazromkzyhic2mgyyjrh4jlnp6djfuotu37btdfolqp5e2o@6jkbjnahvrbo>
Uwe Kleine-König <u.kleine-koenig@pengutronix.de> 於 2024年2月6日 週二 上午2:07寫道：
>
> Hello,
Hi Uwe, thanks for your feedback.
>
> Regarding the Subject: The patch has nothing to do with an LED, has it?
I will correct this.
>
> On Fri, Jan 26, 2024 at 03:40:44PM +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.
>
> Please break lines at 75 columns in the commit log.
got it.
>
> > The reference is SiFive FU740-C000 Manual[0]
> >
> > Link: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf [0]
>
> I looked at Figure 29 in this document (version v1p6, pdf page 148). Not
> sure I understand that correctly, but I expect that the output of the
> ">=?" node below pwmcmp0 to become 1 if pwms has reached pwmcmp0, is
> that right? In that case this output is zero when pwmcount is zero and
> then pwmcmp0ip is zero, too. So a period starts with the inactive part
> and so it's inversed polarity.
>
> What made you think that the current driver implementation is wrong?
This is the process of my speculation.
This is a HiFive Unmatched/Unleashed LED-PWM layout
VDD
|
|
_____
\ / LED
\ /
---
|
|
|
______
| |
- |
^ --> |------ PWM
|___|___|
|
|
__
-
GND
- the waveform
e.g. duty=30s, period=100s, actvie-high = 30%, active-low = 70%
V
^
|
| ----------|
| |
| |
|______ |__________ > t
When VCC is high, the LED will be illuminated, which is an active-high
logic. This is why I want to remove "active-low".
For HW, we just focus on pwmcount/pwmcmp[0-3]
- pwmcount default is zero, that counter 0->1->0xffff
- Follow the origin algorithm the frac=0x0(on) / 0xffff(off) and when
the smaller the value of frac, the brighter the light.
-- E.g. pwmcmp = 0x2, pwmcount 0x0->0x1->...->0xffff
--- 0->0x2=low & 0x3->0xffff=high => 98%
-- E.g. pwmcmp = 0xffff, pwmcount 0x0->0x1->...->0xffff
--- 0->0xffff=low => 0%
- For SW, we reference the algorithm. (D=PW/T*100% D=duty_cycle,
T=period, PW=pulse width (pulse active time))
-- when we consider HW behavior
--- Direct writing SW frac into HW's pwmcmp is active low, so when
we want to get an active-high behavior that use a invert function.
If my understanding or deduction process is incorrect, please let me
know. Thank you.
>
> > Co-developed-by: Zong Li <zong.li@sifive.com>
> > Signed-off-by: Zong Li <zong.li@sifive.com>
> > Co-developed-by: Vincent Chen <vincent.chen@sifive.com>
> > Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
> > Signed-off-by: Nylon Chen <nylon.chen@sifive.com>
> > ---
> > drivers/pwm/pwm-sifive.c | 7 ++++---
> > 1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> > index eabddb7c7820..b07c8598bb21 100644
> > --- a/drivers/pwm/pwm-sifive.c
> > +++ b/drivers/pwm/pwm-sifive.c
> > @@ -113,6 +113,7 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> > u32 duty, val;
> >
> > duty = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
> > + duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - duty;
>
> I find it irritating that both values are assigned to duty. I'd spend
> another variable and make this:
>
> inactive = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
> duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - inactive;
got it.
>
>
> >
> > state->enabled = duty > 0;
> >
> > @@ -123,11 +124,10 @@ static int pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> > state->period = ddata->real_period;
> > state->duty_cycle =
> > (u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH;
> > - state->polarity = PWM_POLARITY_INVERSED;
> > + state->polarity = PWM_POLARITY_NORMAL;
> >
> > return 0;
> > }
> > -
>
> Please keep this empty line between functions.
got it.
>
> > static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > const struct pwm_state *state)
> > {
>
> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-König |
> Industrial Linux Solutions | https://www.pengutronix.de/ |
next prev parent reply other threads:[~2024-02-10 3:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-26 7:40 [PATCH v8 0/3] Change PWM-controlled LED pin active mode and algorithm Nylon Chen
2024-01-26 7:40 ` [PATCH v8 1/3] riscv: dts: sifive: unleashed/unmatched: Remove PWM controlled LED's active-low properties Nylon Chen
2024-01-29 18:23 ` Conor Dooley
2024-01-26 7:40 ` [PATCH v8 2/3] pwm: sifive: change the PWM controlled LED algorithm Nylon Chen
2024-02-05 18:07 ` Uwe Kleine-König
2024-02-10 3:09 ` Nylon Chen [this message]
2024-01-26 7:40 ` [PATCH v8 3/3] pwm: sifive: Fix the error in the idempotent test within the pwm_apply_state_debug function Nylon Chen
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