[PATCH v4 20/24] pwm: add the core infrastructure to allow atomic update

Boris Brezillon
2015-11-16T08:57:34Z

Add an ->apply() method to the pwm_ops struct to allow PWM drivers to
implement atomic update.
This method will be preferred 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>
Tested-by: Heiko Stuebner <heiko@sntech.de>
---
drivers/pwm/core.c | 124 +++++++++++++++++++++++++++++++++++++++++++++++++---
include/linux/pwm.h | 27 ++++++++++++
2 files changed, 146 insertions(+), 5 deletions(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index ce8b373..fbc71d3 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -46,6 +46,12 @@ static struct pwm_device *pwm_to_device(unsigned int pwm)
return radix_tree_lookup(&pwm_tree, pwm);
}

+static void pwm_set_state(struct pwm_device *pwm,
+ const struct pwm_state *state)
+{
+ pwm->state = *state;
+}
+
static int alloc_pwms(int pwm, unsigned int count)
{
unsigned int from = 0;
@@ -226,6 +232,19 @@ 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
@@ -244,8 +263,10 @@ 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);
@@ -446,7 +467,19 @@ 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_get_state(pwm, &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;

@@ -474,6 +507,18 @@ 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_get_state(pwm, &state);
+ 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;

@@ -512,7 +557,17 @@ int pwm_enable(struct pwm_device *pwm)
mutex_lock(&pwm->lock);

if (!pwm_is_enabled(pwm)) {
- err = pwm->chip->ops->enable(pwm->chip, pwm);
+ if (pwm->chip->ops->apply) {
+ struct pwm_state state;
+
+ pwm_get_state(pwm, &state);
+ state.enabled = true;
+
+ err = pwm->chip->ops->apply(pwm->chip, pwm, &state);
+ } else {
+ err = pwm->chip->ops->enable(pwm->chip, pwm);
+ }
+
if (!err)
pwm->state.enabled = true;
}
@@ -535,7 +590,16 @@ void pwm_disable(struct pwm_device *pwm)
mutex_lock(&pwm->lock);

if (pwm_is_enabled(pwm)) {
- pwm->chip->ops->disable(pwm->chip, pwm);
+ if (pwm->chip->ops->apply) {
+ struct pwm_state state;
+
+ pwm_get_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;
}

@@ -543,6 +607,56 @@ void pwm_disable(struct pwm_device *pwm)
}
EXPORT_SYMBOL_GPL(pwm_disable);

+/**
+ * pwm_apply_state() - atomically apply a new state to a PWM device
+ * @pwm: PWM device
+ * @state: new state to apply
+ */
+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_set_state(pwm, state);
+ } 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 caa0ffe..5e7b378 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -174,6 +174,30 @@ static inline enum pwm_polarity pwm_get_polarity(const struct pwm_device *pwm)
return pwm ? pwm->state.polarity : PWM_POLARITY_NORMAL;
}

+int pwm_apply_state(struct pwm_device *pwm, const struct pwm_state *state);
+
+/**
+ * pwm_get_state() - retrieve the current PWM state
+ * @pwm: PWM device
+ * @state: state to fill with the current PWM state
+ */
+static inline void pwm_get_state(struct pwm_device *pwm,
+ struct pwm_state *state)
+{
+ *state = pwm->state;
+}
+
+/**
+ * pwm_get_default_state() - retrieve the default PWM state
+ * @pwm: PWM device
+ * @state: state to fill with the default PWM state
+ */
+static inline void pwm_get_default_state(struct pwm_device *pwm,
+ struct pwm_state *state)
+{
+ *state = pwm->default_state;
+}
+
/**
* struct pwm_ops - PWM controller operations
* @request: optional hook for requesting a PWM
@@ -182,6 +206,7 @@ static inline enum pwm_polarity pwm_get_polarity(const struct pwm_device *pwm)
* @set_polarity: configure the polarity of this PWM
* @enable: enable PWM output toggling
* @disable: disable PWM output toggling
+ * @apply: atomically apply a new PWM config
* @reset_state: reset the current PWM state (pwm->state) to the actual
* hardware state. This function is only called once per
* PWM device when the PWM chip is registered.
@@ -197,6 +222,8 @@ struct pwm_ops {
enum pwm_polarity polarity);
int (*enable)(struct pwm_chip *chip, struct pwm_device *pwm);
void (*disable)(struct pwm_chip *chip, struct pwm_device *pwm);
+ int (*apply)(struct pwm_chip *chip, struct pwm_device *pwm,
+ const struct pwm_state *state);
void (*reset_state)(struct pwm_chip *chip, struct pwm_device *pwm);
#ifdef CONFIG_DEBUG_FS
void (*dbg_show)(struct pwm_chip *chip, struct seq_file *s);
--
2.1.4