Re: [PATCH v3] pwm: bcm2835: Support apply function for atomic configuration

[Uwe Kleine-König]

Hello Lino,

On Tue, Dec 08, 2020 at 11:01:45PM +0100, Lino Sanfilippo wrote:
> Use the newer .apply function of pwm_ops instead of .config, .enable,
> .disable and .set_polarity. This guarantees atomic changes of the pwm
> controller configuration. It also reduces the size of the driver.
> 
> Since now period is a 64 bit value, add an extra check to reject periods
> that exceed the possible max value for the 32 bit register.
> 
> This has been tested on a Raspberry PI 4.

This looks right, just two small nitpicks below.

> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@xxxxxx>
> ---
> 
> v3: Check against period truncation (based on a review by Uwe Kleine-König)
> v2: Fix compiler error for 64 bit builds
> 
>  drivers/pwm/pwm-bcm2835.c | 72 +++++++++++++++++------------------------------
>  1 file changed, 26 insertions(+), 46 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c
> index 6841dcf..d339898 100644
> --- a/drivers/pwm/pwm-bcm2835.c
> +++ b/drivers/pwm/pwm-bcm2835.c
> @@ -58,13 +58,15 @@ static void bcm2835_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
>  	writel(value, pc->base + PWM_CONTROL);
>  }
>  
> -static int bcm2835_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> -			      int duty_ns, int period_ns)
> +static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			     const struct pwm_state *state)
>  {
> +
>  	struct bcm2835_pwm *pc = to_bcm2835_pwm(chip);
>  	unsigned long rate = clk_get_rate(pc->clk);
> +	unsigned long long period;
>  	unsigned long scaler;
> -	u32 period;
> +	u32 val;
>  
>  	if (!rate) {
>  		dev_err(pc->dev, "failed to get clock rate\n");
> @@ -72,65 +74,43 @@ static int bcm2835_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>  	}
>  
>  	scaler = DIV_ROUND_CLOSEST(NSEC_PER_SEC, rate);
> -	period = DIV_ROUND_CLOSEST(period_ns, scaler);
> +	/* set period */
> +	period = DIV_ROUND_CLOSEST_ULL(state->period, scaler);
>  
> -	if (period < PERIOD_MIN)
> +	/* dont accept a period that is too small or has been truncated */
> +	if ((period < PERIOD_MIN) || (period > U32_MAX))
>  		return -EINVAL;
>  
> -	writel(DIV_ROUND_CLOSEST(duty_ns, scaler),
> -	       pc->base + DUTY(pwm->hwpwm));
> -	writel(period, pc->base + PERIOD(pwm->hwpwm));
> -
> -	return 0;
> -}
> -
> -static int bcm2835_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> -{
> -	struct bcm2835_pwm *pc = to_bcm2835_pwm(chip);
> -	u32 value;
> -
> -	value = readl(pc->base + PWM_CONTROL);
> -	value |= PWM_ENABLE << PWM_CONTROL_SHIFT(pwm->hwpwm);
> -	writel(value, pc->base + PWM_CONTROL);
> -
> -	return 0;
> -}
> -
> -static void bcm2835_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> -{
> -	struct bcm2835_pwm *pc = to_bcm2835_pwm(chip);
> -	u32 value;
> +	writel((u32) period, pc->base + PERIOD(pwm->hwpwm));

This cast isn't necessary. (And if it was, I *think* the space between
"(u32)" and "period" is wrong. But my expectation that checkpatch warns
about this is wrong, so take this with a grain of salt.)

> -	value = readl(pc->base + PWM_CONTROL);
> -	value &= ~(PWM_ENABLE << PWM_CONTROL_SHIFT(pwm->hwpwm));
> -	writel(value, pc->base + PWM_CONTROL);
> -}
> +	/* set duty cycle */
> +	val = DIV_ROUND_CLOSEST_ULL(state->duty_cycle, scaler);
> +	writel(val, pc->base + DUTY(pwm->hwpwm));
>  
> -static int bcm2835_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
> -				enum pwm_polarity polarity)
> -{
> -	struct bcm2835_pwm *pc = to_bcm2835_pwm(chip);
> -	u32 value;
> +	/* set polarity */
> +	val = readl(pc->base + PWM_CONTROL);
>  
> -	value = readl(pc->base + PWM_CONTROL);
> +	if (state->polarity == PWM_POLARITY_NORMAL)
> +		val &= ~(PWM_POLARITY << PWM_CONTROL_SHIFT(pwm->hwpwm));
> +	else
> +		val |= PWM_POLARITY << PWM_CONTROL_SHIFT(pwm->hwpwm);
>  
> -	if (polarity == PWM_POLARITY_NORMAL)
> -		value &= ~(PWM_POLARITY << PWM_CONTROL_SHIFT(pwm->hwpwm));
> +	/* enable/disable */
> +	if (state->enabled)
> +		val |= PWM_ENABLE << PWM_CONTROL_SHIFT(pwm->hwpwm);
>  	else
> -		value |= PWM_POLARITY << PWM_CONTROL_SHIFT(pwm->hwpwm);
> +		val &= ~(PWM_ENABLE << PWM_CONTROL_SHIFT(pwm->hwpwm));
>  
> -	writel(value, pc->base + PWM_CONTROL);
> +	writel(val, pc->base + PWM_CONTROL);
>  
>  	return 0;
>  }
>  
> +

I wouldn't have added this empty line. But I guess that's subjective. Or
did you add this by mistake?

>  static const struct pwm_ops bcm2835_pwm_ops = {
>  	.request = bcm2835_pwm_request,
>  	.free = bcm2835_pwm_free,
> -	.config = bcm2835_pwm_config,
> -	.enable = bcm2835_pwm_enable,
> -	.disable = bcm2835_pwm_disable,
> -	.set_polarity = bcm2835_set_polarity,
> +	.apply = bcm2835_pwm_apply,
>  	.owner = THIS_MODULE,
>  };

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

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