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Date: Mon, 18 Mar 2024 19:16:14 +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 v9 2/3] pwm: sifive: change the PWM algorithm
Message-ID: <f5ukvah2ujko2iht3pd5jxq5kaukbs5z3pn5s7qwcnx4aqr3yv@mwtbwkcfa44a>
References: <20240222081231.213406-1-nylon.chen@sifive.com>
 <20240222081231.213406-3-nylon.chen@sifive.com>
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On Thu, Feb 22, 2024 at 04:12:30PM +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.
>=20
> 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]
>=20
> 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 | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>=20
> diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> index eabddb7c7820..a586cfe4191b 100644
> --- a/drivers/pwm/pwm-sifive.c
> +++ b/drivers/pwm/pwm-sifive.c
> @@ -110,9 +110,10 @@ static int pwm_sifive_get_state(struct pwm_chip *chi=
p, struct pwm_device *pwm,
>  				struct pwm_state *state)
>  {
>  	struct pwm_sifive_ddata *ddata =3D pwm_sifive_chip_to_ddata(chip);
> -	u32 duty, val;
> +	u32 duty, val, inactive;
> =20
> -	duty =3D readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
> +	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
> @@ -123,7 +124,7 @@ static int pwm_sifive_get_state(struct pwm_chip *chip=
, 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;
>  }
> @@ -139,7 +140,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, st=
ruct pwm_device *pwm,
>  	int ret =3D 0;
>  	u32 frac;
> =20
> -	if (state->polarity !=3D PWM_POLARITY_INVERSED)
> +	if (state->polarity !=3D PWM_POLARITY_NORMAL)
>  		return -EINVAL;
> =20
>  	cur_state =3D pwm->state;
> @@ -159,6 +160,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, st=
ruct pwm_device *pwm,
>  	frac =3D DIV64_U64_ROUND_CLOSEST(num, state->period);
>  	/* The hardware cannot generate a 100% duty cycle */

Is this still true now that we know that PWM_SIFIVE_PWMCMP is the
inactive time in a period? If you fix that, the same claim in the header
of the driver needs adaption, too.

>  	frac =3D min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
> +	frac =3D (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;

I like the additional variable in pwm_sifive_get_state(). Can you please
add one here, too?

>  	mutex_lock(&ddata->lock);
>  	if (state->period !=3D ddata->approx_period) {

Best regards
Uwe

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

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