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

Thierry Reding
2015-07-20T08:59:40Z

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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 <boris.brezillon@free-electrons.com>
> ---
> 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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