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

On Mon, 20 Jul 2015 10:59:40 +0200
Thierry Reding [off-list ref] wrote:

On Wed, Jul 01, 2015 at 10:21:57AM +0200, Boris Brezillon wrote:

quoted

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 <redacted>
---
 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;

Sure, I'll change that to make it more readable.

quoted

 	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()?

Yes, I'll fix all of them

[...]

quoted

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

There should be a space between the above two lines.

I'll add an empty line.

quoted

 
+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?

I'm not opposed to the addition of the pwm_set_state() function as long
as it's a private one: I don't want to let PMW drivers or users mess up
with the current PWM state.

quoted

+	} 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.

Yes, I'll fix that.
BTW, I remember that you were expecting another name for this function
(pwm_update IIRC).



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com