linux-kernel - Re: [PATCH] pwm: stm32: Implement .get

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Message-ID: <ZLY_gER7FeEB07cw@orome>
Date:   Tue, 18 Jul 2023 09:30:08 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Fabrice Gasnier <fabrice.gasnier@...s.st.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        linux-pwm@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pwm: stm32: Implement .get_state()

On Thu, Jun 08, 2023 at 04:06:02PM +0200, Philipp Zabel wrote:
> Stop stm32_pwm_detect_channels() from disabling all channels and count
> the number of enabled PWMs to keep the clock running. Implement the
> &pwm_ops->get_state callback so drivers can inherit PWM state set by
> the bootloader.
> 
> Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
> ---
> Make the necessary changes to allow inheriting PWM state set by the
> bootloader, for example to avoid flickering with a pre-enabled PWM
> backlight.
> ---
>  drivers/pwm/pwm-stm32.c | 75 ++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 59 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c
> index 62e397aeb9aa..e0677c954bdf 100644
> --- a/drivers/pwm/pwm-stm32.c
> +++ b/drivers/pwm/pwm-stm32.c
> @@ -52,6 +52,21 @@ static u32 active_channels(struct stm32_pwm *dev)
>  	return ccer & TIM_CCER_CCXE;
>  }
>  
> +static int read_ccrx(struct stm32_pwm *dev, int ch, u32 *value)
> +{
> +	switch (ch) {
> +	case 0:
> +		return regmap_read(dev->regmap, TIM_CCR1, value);
> +	case 1:
> +		return regmap_read(dev->regmap, TIM_CCR2, value);
> +	case 2:
> +		return regmap_read(dev->regmap, TIM_CCR3, value);
> +	case 3:
> +		return regmap_read(dev->regmap, TIM_CCR4, value);
> +	}
> +	return -EINVAL;
> +}

Looking at the register definitions we should be able to replace this
with a single line and parameterize based on channel.

I realize you probably just copied from write_ccrx(), but might as well
improve this while at it. Could be a separate patch, though.

Also, ch should be unsigned int since it comes from pwm->hwpwm.

> +
>  static int write_ccrx(struct stm32_pwm *dev, int ch, u32 value)
>  {
>  	switch (ch) {
> @@ -486,9 +501,40 @@ static int stm32_pwm_apply_locked(struct pwm_chip *chip, struct pwm_device *pwm,
>  	return ret;
>  }
>  
> +static int stm32_pwm_get_state(struct pwm_chip *chip,
> +			       struct pwm_device *pwm, struct pwm_state *state)
> +{
> +	struct stm32_pwm *priv = to_stm32_pwm_dev(chip);
> +	int ch = pwm->hwpwm;

This should reflect the type of pwm->hwpwm.

> +	unsigned long rate;
> +	u32 ccer, psc, arr, ccr;
> +	u64 dty, prd;
> +	int ret;
> +
> +	ret = regmap_read(priv->regmap, TIM_CCER, &ccer);
> +	if (ret)
> +		return ret;
> +
> +	state->enabled = ccer & (TIM_CCER_CC1E << (ch * 4));
> +	state->polarity = (ccer & (TIM_CCER_CC1P << (ch * 4))) ?
> +			  PWM_POLARITY_INVERSED : PWM_POLARITY_NORMAL;
> +	regmap_read(priv->regmap, TIM_PSC, &psc);
> +	regmap_read(priv->regmap, TIM_ARR, &arr);

We should probably check regmap_read() consistently here.

> +	read_ccrx(priv, ch, &ccr);
> +	rate = clk_get_rate(priv->clk);
> +
> +	prd = (u64)NSEC_PER_SEC * (psc + 1) * (arr + 1);
> +	state->period = DIV_ROUND_UP_ULL(prd, rate);
> +	dty = (u64)NSEC_PER_SEC * (psc + 1) * ccr;
> +	state->duty_cycle = DIV_ROUND_UP_ULL(dty, rate);
> +
> +	return ret;
> +}
> +
>  static const struct pwm_ops stm32pwm_ops = {
>  	.owner = THIS_MODULE,
>  	.apply = stm32_pwm_apply_locked,
> +	.get_state = stm32_pwm_get_state,
>  	.capture = IS_ENABLED(CONFIG_DMA_ENGINE) ? stm32_pwm_capture : NULL,
>  };
>  
> @@ -579,30 +625,22 @@ static void stm32_pwm_detect_complementary(struct stm32_pwm *priv)
>  	priv->have_complementary_output = (ccer != 0);
>  }
>  
> -static int stm32_pwm_detect_channels(struct stm32_pwm *priv)
> +static int stm32_pwm_detect_channels(struct stm32_pwm *priv, int *n_enabled)

unsigned int * for n_enabled.

>  {
> -	u32 ccer;
> -	int npwm = 0;
> +	u32 ccer, ccer_backup;
> +	int npwm;

Also make this and the return value unsigned int while at it. These can
never be negative.

Thierry

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