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pwm: Add core infrastructure to allow atomic updates
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Add an ->apply() method to the pwm_ops struct to allow PWM drivers to
implement atomic updates. This method is preferred over the ->enable(),
->disable() and ->config() methods if available.

Add the pwm_apply_state() function to the PWM user API.

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.

pwm_enable/disable/set_polarity/config() are now implemented as wrappers
around the pwm_apply_state() function.

pwm_adjust_config() is allowing smooth handover between the bootloader
and the kernel. This function tries to adapt the current PWM state to
the PWM arguments coming from a PWM lookup table or a DT definition
without changing the duty_cycle/period proportion.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
[thierry.reding@gmail.com: fix a couple of typos]
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
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Boris Brezillon authored and Thierry Reding committed May 17, 2016
1 parent 15fa8a4 commit 5ec803e
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Showing 2 changed files with 303 additions and 153 deletions.
187 changes: 119 additions & 68 deletions drivers/pwm/core.c
Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,19 @@ void *pwm_get_chip_data(struct pwm_device *pwm)
}
EXPORT_SYMBOL_GPL(pwm_get_chip_data);

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;
}

/**
* pwmchip_add_with_polarity() - register a new PWM chip
* @chip: the PWM chip to add
Expand All @@ -244,8 +257,10 @@ 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->npwm)
return -EINVAL;

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

mutex_lock(&pwm_lock);
Expand Down Expand Up @@ -431,102 +446,138 @@ void pwm_free(struct pwm_device *pwm)
EXPORT_SYMBOL_GPL(pwm_free);

/**
* pwm_config() - change a PWM device configuration
* pwm_apply_state() - atomically apply a new state to a PWM device
* @pwm: PWM device
* @duty_ns: "on" time (in nanoseconds)
* @period_ns: duration (in nanoseconds) of one cycle
*
* Returns: 0 on success or a negative error code on failure.
* @state: new state to apply. This can be adjusted by the PWM driver
* if the requested config is not achievable, for example,
* ->duty_cycle and ->period might be approximated.
*/
int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state)
{
int err;

if (!pwm || duty_ns < 0 || period_ns <= 0 || duty_ns > period_ns)
if (!pwm)
return -EINVAL;

err = pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
if (err)
return err;

pwm->state.duty_cycle = duty_ns;
pwm->state.period = period_ns;

return 0;
}
EXPORT_SYMBOL_GPL(pwm_config);
if (!memcmp(state, &pwm->state, sizeof(*state)))
return 0;

/**
* pwm_set_polarity() - configure the polarity of a PWM signal
* @pwm: PWM device
* @polarity: new polarity of the PWM signal
*
* Note that the polarity cannot be configured while the PWM device is
* enabled.
*
* Returns: 0 on success or a negative error code on failure.
*/
int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
{
int err;
if (pwm->chip->ops->apply) {
err = pwm->chip->ops->apply(pwm->chip, pwm, state);
if (err)
return err;

if (!pwm || !pwm->chip->ops)
return -EINVAL;
pwm->state = *state;
} else {
/*
* FIXME: restore the initial state in case of error.
*/
if (state->polarity != pwm->state.polarity) {
if (!pwm->chip->ops->set_polarity)
return -ENOTSUPP;

/*
* Changing the polarity of a running PWM is
* only allowed when the PWM driver implements
* ->apply().
*/
if (pwm->state.enabled) {
pwm->chip->ops->disable(pwm->chip, pwm);
pwm->state.enabled = false;
}

err = pwm->chip->ops->set_polarity(pwm->chip, pwm,
state->polarity);
if (err)
return err;

pwm->state.polarity = state->polarity;
}

if (!pwm->chip->ops->set_polarity)
return -ENOSYS;
if (state->period != pwm->state.period ||
state->duty_cycle != pwm->state.duty_cycle) {
err = pwm->chip->ops->config(pwm->chip, pwm,
state->duty_cycle,
state->period);
if (err)
return err;

if (pwm_is_enabled(pwm))
return -EBUSY;
pwm->state.duty_cycle = state->duty_cycle;
pwm->state.period = state->period;
}

err = pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
if (err)
return err;
if (state->enabled != pwm->state.enabled) {
if (state->enabled) {
err = pwm->chip->ops->enable(pwm->chip, pwm);
if (err)
return err;
} else {
pwm->chip->ops->disable(pwm->chip, pwm);
}

pwm->state.polarity = polarity;
pwm->state.enabled = state->enabled;
}
}

return 0;
}
EXPORT_SYMBOL_GPL(pwm_set_polarity);
EXPORT_SYMBOL_GPL(pwm_apply_state);

/**
* pwm_enable() - start a PWM output toggling
* pwm_adjust_config() - adjust the current PWM config to the PWM arguments
* @pwm: PWM device
*
* Returns: 0 on success or a negative error code on failure.
* This function will adjust the PWM config to the PWM arguments provided
* by the DT or PWM lookup table. This is particularly useful to adapt
* the bootloader config to the Linux one.
*/
int pwm_enable(struct pwm_device *pwm)
int pwm_adjust_config(struct pwm_device *pwm)
{
int err = 0;
struct pwm_state state;
struct pwm_args pargs;

if (!pwm)
return -EINVAL;
pwm_get_args(pwm, &pargs);
pwm_get_state(pwm, &state);

/*
* If the current period is zero it means that either the PWM driver
* does not support initial state retrieval or the PWM has not yet
* been configured.
*
* In either case, we setup the new period and polarity, and assign a
* duty cycle of 0.
*/
if (!state.period) {
state.duty_cycle = 0;
state.period = pargs.period;
state.polarity = pargs.polarity;

if (!pwm_is_enabled(pwm)) {
err = pwm->chip->ops->enable(pwm->chip, pwm);
if (!err)
pwm->state.enabled = true;
return pwm_apply_state(pwm, &state);
}

return err;
}
EXPORT_SYMBOL_GPL(pwm_enable);
/*
* Adjust the PWM duty cycle/period based on the period value provided
* in PWM args.
*/
if (pargs.period != state.period) {
u64 dutycycle = (u64)state.duty_cycle * pargs.period;

/**
* pwm_disable() - stop a PWM output toggling
* @pwm: PWM device
*/
void pwm_disable(struct pwm_device *pwm)
{
if (!pwm)
return;
do_div(dutycycle, state.period);
state.duty_cycle = dutycycle;
state.period = pargs.period;
}

if (pwm_is_enabled(pwm)) {
pwm->chip->ops->disable(pwm->chip, pwm);
pwm->state.enabled = false;
/*
* If the polarity changed, we should also change the duty cycle.
*/
if (pargs.polarity != state.polarity) {
state.polarity = pargs.polarity;
state.duty_cycle = state.period - state.duty_cycle;
}

return pwm_apply_state(pwm, &state);
}
EXPORT_SYMBOL_GPL(pwm_disable);
EXPORT_SYMBOL_GPL(pwm_adjust_config);

static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
{
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