pwm: Make it possible to apply PWM changes in atomic context

Some PWM devices require sleeping, for example if the pwm device is
connected over I2C. However, many PWM devices could be used from atomic
context, e.g. memory mapped PWM. This is useful for, for example, the
pwm-ir-tx driver which requires precise timing. Sleeping causes havoc
with the generated IR signal.

Since not all PWM devices can support atomic context, we also add a
pwm_might_sleep() function to check if is not supported.

Signed-off-by: Sean Young <sean@mess.org>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

1 files changed, 51 insertions, 11 deletions

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index c6228843a1a7..f1ded8ce5ea4 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -433,24 +433,15 @@ static void pwm_apply_debug(struct pwm_device *pwm,
 }
 
 /**
- * pwm_apply_might_sleep() - atomically apply a new state to a PWM device
+ * __pwm_apply() - atomically apply a new state to a PWM device
  * @pwm: PWM device
  * @state: new state to apply
  */
-int pwm_apply_might_sleep(struct pwm_device *pwm, const struct pwm_state *state)
+static int __pwm_apply(struct pwm_device *pwm, const struct pwm_state *state)
 {
 	struct pwm_chip *chip;
 	int err;
 
-	/*
-	 * Some lowlevel driver's implementations of .apply() make use of
-	 * mutexes, also with some drivers only returning when the new
-	 * configuration is active calling pwm_apply_might_sleep() from atomic context
-	 * is a bad idea. So make it explicit that calling this function might
-	 * sleep.
-	 */
-	might_sleep();
-
 	if (!pwm || !state || !state->period ||
 	    state->duty_cycle > state->period)
 		return -EINVAL;
@@ -479,9 +470,58 @@ int pwm_apply_might_sleep(struct pwm_device *pwm, const struct pwm_state *state)
 
 	return 0;
 }
+
+/**
+ * pwm_apply_might_sleep() - atomically apply a new state to a PWM device
+ * Cannot be used in atomic context.
+ * @pwm: PWM device
+ * @state: new state to apply
+ */
+int pwm_apply_might_sleep(struct pwm_device *pwm, const struct pwm_state *state)
+{
+	int err;
+
+	/*
+	 * Some lowlevel driver's implementations of .apply() make use of
+	 * mutexes, also with some drivers only returning when the new
+	 * configuration is active calling pwm_apply_might_sleep() from atomic context
+	 * is a bad idea. So make it explicit that calling this function might
+	 * sleep.
+	 */
+	might_sleep();
+
+	if (IS_ENABLED(CONFIG_PWM_DEBUG) && pwm->chip->atomic) {
+		/*
+		 * Catch any drivers that have been marked as atomic but
+		 * that will sleep anyway.
+		 */
+		non_block_start();
+		err = __pwm_apply(pwm, state);
+		non_block_end();
+	} else {
+		err = __pwm_apply(pwm, state);
+	}
+
+	return err;
+}
 EXPORT_SYMBOL_GPL(pwm_apply_might_sleep);
 
 /**
+ * pwm_apply_atomic() - apply a new state to a PWM device from atomic context
+ * Not all PWM devices support this function, check with pwm_might_sleep().
+ * @pwm: PWM device
+ * @state: new state to apply
+ */
+int pwm_apply_atomic(struct pwm_device *pwm, const struct pwm_state *state)
+{
+	WARN_ONCE(!pwm->chip->atomic,
+		  "sleeping PWM driver used in atomic context\n");
+
+	return __pwm_apply(pwm, state);
+}
+EXPORT_SYMBOL_GPL(pwm_apply_atomic);
+
+/**
  * pwm_capture() - capture and report a PWM signal
  * @pwm: PWM device
  * @result: structure to fill with capture result