Subject: [RFC PATCH 11/15] pwm: add the core infrastructure to allow atomic update

From: [email-masked] (Thierry Reding)
Date: Mon, 20 Jul 2015 10:59:40 +0200

On Wed, Jul 01, 2015 at 10:21:57AM +0200, Boris Brezillon wrote:
> Add an ->apply() method to the pwm_ops struct to allow PWM drivers to
> implement atomic update.
> This method will be prefered over the ->enable(), ->disable() and
> ->config() methods if available.
> 
> Add the pwm_get_state(), pwm_get_default_state() and pwm_apply_state()
> functions for PWM users to be able to use the atomic update feature.
> 
> Note that the pwm_apply_state() does not guarantee the atomicity of the
> update operation, it all depends on the availability and implementation
> of the ->apply() method.
> 
> Signed-off-by: Boris Brezillon <[email-masked]>
> ---
>  drivers/pwm/core.c  | 110 ++++++++++++++++++++++++++++++++++++++++++++++------
>  include/linux/pwm.h |  26 +++++++++++++
>  2 files changed, 124 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 30631f5..6dafd8e 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -238,8 +238,9 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
>  	unsigned int i;
>  	int ret;
>  
> -	if (!chip || !chip->dev || !chip->ops || !chip->ops->config ||
> -	    !chip->ops->enable || !chip->ops->disable || !chip->npwm)
> +	if (!chip || !chip->dev || !chip->ops || (!chip->ops->apply &&
> +	    (!chip->ops->config || !chip->ops->enable ||
> +	     !chip->ops->disable)) || !chip->npwm)
>  		return -EINVAL;

This is becoming really unreadable, perhaps split it into two checks, or
even split out the sanity check on the ops into a separate function to
make the negations easier to read:

	static bool pwm_ops_check(const struct pwm_ops *ops)
	{
		/* driver supports legacy, non-atomic operation */
		if (ops->config && ops->enable && ops->disable)
			return true;

		/* driver supports atomic operation */
		if (ops->apply)
			return true;

		return false;
	}

and then use this:

	if (!chip || !chip->dev || !chip->ops || !chip->npwm)
		return -EINVAL;

	if (!pwm_ops_check(chip->ops))
		return -EINVAL;

>  	mutex_lock(&pwm_lock);
> @@ -430,7 +431,17 @@ int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
>  	if (!pwm || duty_ns < 0 || period_ns <= 0 || duty_ns > period_ns)
>  		return -EINVAL;
>  
> -	err = pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
> +	if (pwm->chip->ops->apply) {
> +		struct pwm_state state = pwm->state;

Shouldn't this use pwm_get_state()?

> +
> +		state.period = period_ns;
> +		state.duty_cycle = duty_ns;
> +
> +		err = pwm->chip->ops->apply(pwm->chip, pwm, &state);
> +	} else {
> +		err = pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
> +	}
> +
>  	if (err)
>  		return err;
>  
> @@ -455,6 +466,17 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
>  	if (!pwm || !pwm->chip->ops)
>  		return -EINVAL;
>  
> +	if (pwm->chip->ops->apply) {
> +		struct pwm_state state = pwm->state;

Same here.

> +
> +		state.polarity = polarity;
> +		err = pwm->chip->ops->apply(pwm->chip, pwm, &state);
> +		if (!err)
> +			pwm->state.polarity = polarity;
> +
> +		return err;
> +	}
> +
>  	if (!pwm->chip->ops->set_polarity)
>  		return -ENOSYS;
>  
> @@ -477,17 +499,27 @@ EXPORT_SYMBOL_GPL(pwm_set_polarity);
>   */
>  int pwm_enable(struct pwm_device *pwm)
>  {
> -	if (pwm && !pwm_is_enabled(pwm)) {
> -		int err;
> +	int err;
>  
> -		err = pwm->chip->ops->enable(pwm->chip, pwm);
> -		if (!err)
> -			pwm->state.enabled = true;
> +	if (!pwm)
> +		return -EINVAL;
>  
> -		return err;
> +	if (pwm_is_enabled(pwm))
> +		return 0;
> +
> +	if (pwm->chip->ops->apply) {
> +		struct pwm_state state = pwm->state;

And here.

> +
> +		state.enabled = true;
> +		err = pwm->chip->ops->apply(pwm->chip, pwm, &state);

There should be a space between the above two lines.

> +	} else {
> +		err = pwm->chip->ops->enable(pwm->chip, pwm);
>  	}
>  
> -	return pwm ? 0 : -EINVAL;
> +	if (!err)
> +		pwm->state.enabled = true;
> +
> +	return err;
>  }
>  EXPORT_SYMBOL_GPL(pwm_enable);
>  
> @@ -497,13 +529,67 @@ EXPORT_SYMBOL_GPL(pwm_enable);
>   */
>  void pwm_disable(struct pwm_device *pwm)
>  {
> -	if (pwm && pwm_is_enabled(pwm)) {
> +	if (!pwm || !pwm_is_enabled(pwm))
> +		return;
> +
> +	if (pwm->chip->ops->apply) {
> +		struct pwm_state state = pwm->state;
> +
> +		state.enabled = false;
> +		pwm->chip->ops->apply(pwm->chip, pwm, &state);
> +	} else {
>  		pwm->chip->ops->disable(pwm->chip, pwm);
> -		pwm->state.enabled = false;
>  	}
> +
> +	pwm->state.enabled = false;
>  }
>  EXPORT_SYMBOL_GPL(pwm_disable);

Same comments as for pwm_enable().

>  
> +int pwm_apply_state(struct pwm_device *pwm, const struct pwm_state *state)
> +{
> +	int err = 0;
> +
> +	if (!pwm)
> +		return -EINVAL;
> +
> +	if (!memcmp(state, &pwm->state, sizeof(*state)))
> +		return 0;
> +
> +	if (pwm->chip->ops->apply) {
> +		err = pwm->chip->ops->apply(pwm->chip, pwm, state);
> +		if (!err)
> +			pwm->state = *state;

Maybe we want pwm_set_state() for this?

> +	} else {
> +		/*
> +		 * FIXME: restore the initial state in case of error.
> +		 */
> +		if (state->polarity != pwm->state.polarity) {
> +			pwm_disable(pwm);
> +			err = pwm_set_polarity(pwm, state->polarity);
> +			if (err)
> +				goto out;
> +		}
> +
> +		if (state->period != pwm->state.period ||
> +		    state->duty_cycle != pwm->state.duty_cycle) {
> +			err = pwm_config(pwm, state->period, state->duty_cycle);
> +			if (err)
> +				goto out;
> +		}
> +
> +		if (state->enabled != pwm->state.enabled) {
> +			if (state->enabled)
> +				err = pwm_enable(pwm);
> +			else
> +				pwm_disable(pwm);
> +		}
> +	}
> +
> +out:
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(pwm_apply_state);
> +
>  static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
>  {
>  	struct pwm_chip *chip;
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index b47244a..7e99679 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -151,6 +151,29 @@ static inline enum pwm_polarity pwm_get_polarity(const struct pwm_device *pwm)
>  	return pwm ? pwm->state.polarity : PWM_POLARITY_NORMAL;
>  }
>  
> +/*
> + * pwm_apply_state - apply a new state to the PWM device
> + */
> +int pwm_apply_state(struct pwm_device *pwm, const struct pwm_state *state);

If you add kerneldoc, please add it properly. It should start with /**
and you need to list at least the parameters and return value.

Thierry
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