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Date: Mon, 5 Feb 2024 19:07:13 +0100
From: Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To: Nylon Chen <nylon.chen@sifive.com>
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
Message-ID: <4kqkazromkzyhic2mgyyjrh4jlnp6djfuotu37btdfolqp5e2o@6jkbjnahvrbo>
References: <20240126074045.20159-1-nylon.chen@sifive.com>
 <20240126074045.20159-3-nylon.chen@sifive.com>
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Hello,

Regarding the Subject: The patch has nothing to do with an LED, has it?

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 th=
e result.

Please break lines at 75 columns in the commit log.

> The reference is SiFive FU740-C000 Manual[0]
>=20
> Link: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b=
16acba_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
">=3D?" 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?

> 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(-)
>=20
> 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;
> =20
>  	duty =3D readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
> +	duty =3D (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 =3D readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
	duty =3D (1U << PWM_SIFIVE_CMPWIDTH) - 1 - inactive;


> =20
>  	state->enabled =3D duty > 0;
> =20
> @@ -123,11 +124,10 @@ static int pwm_sifive_get_state(struct pwm_chip *ch=
ip, struct pwm_device *pwm,
>  	state->period =3D ddata->real_period;
>  	state->duty_cycle =3D
>  		(u64)duty * ddata->real_period >> PWM_SIFIVE_CMPWIDTH;
> -	state->polarity =3D PWM_POLARITY_INVERSED;
> +	state->polarity =3D PWM_POLARITY_NORMAL;
> =20
>  	return 0;
>  }
> -

Please keep this empty line between functions.

>  static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pw=
m,
>  			    const struct pwm_state *state)
>  {

Best regards
Uwe

--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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