linux-kernel - Re: [PATCH v9 2/3] pwm: sifive: change the PWM algorithm

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Message-ID: <f5ukvah2ujko2iht3pd5jxq5kaukbs5z3pn5s7qwcnx4aqr3yv@mwtbwkcfa44a>
Date: Mon, 18 Mar 2024 19:16:14 +0100
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Nylon Chen <nylon.chen@...ive.com>
Cc: linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org, conor@...nel.org, robh+dt@...nel.org, 
	krzysztof.kozlowski+dt@...aro.org, palmer@...belt.com, paul.walmsley@...ive.com, 
	aou@...s.berkeley.edu, thierry.reding@...il.com, vincent.chen@...ive.com, 
	zong.li@...ive.com, nylon7717@...il.com
Subject: Re: [PATCH v9 2/3] pwm: sifive: change the PWM algorithm

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.
> 
> 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]
> 
> Co-developed-by: Zong Li <zong.li@...ive.com>
> Signed-off-by: Zong Li <zong.li@...ive.com>
> Co-developed-by: Vincent Chen <vincent.chen@...ive.com>
> Signed-off-by: Vincent Chen <vincent.chen@...ive.com>
> Signed-off-by: Nylon Chen <nylon.chen@...ive.com>
> ---
>  drivers/pwm/pwm-sifive.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> 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 *chip, struct pwm_device *pwm,
>  				struct pwm_state *state)
>  {
>  	struct pwm_sifive_ddata *ddata = pwm_sifive_chip_to_ddata(chip);
> -	u32 duty, val;
> +	u32 duty, val, inactive;
>  
> -	duty = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
> +	inactive = readl(ddata->regs + PWM_SIFIVE_PWMCMP(pwm->hwpwm));
> +	duty = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - inactive;
>  
>  	state->enabled = duty > 0;
>  
> @@ -123,7 +124,7 @@ 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;
>  }
> @@ -139,7 +140,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	int ret = 0;
>  	u32 frac;
>  
> -	if (state->polarity != PWM_POLARITY_INVERSED)
> +	if (state->polarity != PWM_POLARITY_NORMAL)
>  		return -EINVAL;
>  
>  	cur_state = pwm->state;
> @@ -159,6 +160,7 @@ 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 */

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 = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
> +	frac = (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 != ddata->approx_period) {

Best regards
Uwe

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

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