pwm: Ensure callbacks exist before calling them

If one of the waveform functions is called for a chip that only supports
.apply(), we want that an error code is returned and not a NULL pointer
exception.

Fixes: 6c5126c ("pwm: Provide new consumer API functions for waveforms")
Cc: stable@vger.kernel.org
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Tested-by: Trevor Gamblin <tgamblin@baylibre.com>
Link: https://lore.kernel.org/r/20250123172709.391349-2-u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

drivers/pwm/core.c

@@ -242,6 +242,9 @@ int pwm_round_waveform_might_sleep(struct pwm_device *pwm, struct pwm_waveform *
 
 	BUG_ON(WFHWSIZE < ops->sizeof_wfhw);
 
+	if (!pwmchip_supports_waveform(chip))
+		return -EOPNOTSUPP;
+
 	if (!pwm_wf_valid(wf))
 		return -EINVAL;
 
@@ -294,6 +297,9 @@ int pwm_get_waveform_might_sleep(struct pwm_device *pwm, struct pwm_waveform *wf
 
 	BUG_ON(WFHWSIZE < ops->sizeof_wfhw);
 
+	if (!pwmchip_supports_waveform(chip) || !ops->read_waveform)
+		return -EOPNOTSUPP;
+
 	guard(pwmchip)(chip);
 
 	if (!chip->operational)
@@ -320,6 +326,9 @@ static int __pwm_set_waveform(struct pwm_device *pwm,
 
 	BUG_ON(WFHWSIZE < ops->sizeof_wfhw);
 
+	if (!pwmchip_supports_waveform(chip))
+		return -EOPNOTSUPP;
+
 	if (!pwm_wf_valid(wf))
 		return -EINVAL;
 
@@ -592,7 +601,7 @@ static int __pwm_apply(struct pwm_device *pwm, const struct pwm_state *state)
 	    state->usage_power == pwm->state.usage_power)
 		return 0;
 
-	if (ops->write_waveform) {
+	if (pwmchip_supports_waveform(chip)) {
 		struct pwm_waveform wf;
 		char wfhw[WFHWSIZE];
 
@@ -746,7 +755,7 @@ int pwm_get_state_hw(struct pwm_device *pwm, struct pwm_state *state)
 	if (!chip->operational)
 		return -ENODEV;
 
-	if (ops->read_waveform) {
+	if (pwmchip_supports_waveform(chip) && ops->read_waveform) {
 		char wfhw[WFHWSIZE];
 		struct pwm_waveform wf;
 

include/linux/pwm.h

@@ -347,6 +347,23 @@ struct pwm_chip {
 	struct pwm_device pwms[] __counted_by(npwm);
 };
 
+/**
+ * pwmchip_supports_waveform() - checks if the given chip supports waveform callbacks
+ * @chip: The pwm_chip to test
+ *
+ * Returns true iff the pwm chip support the waveform functions like
+ * pwm_set_waveform_might_sleep() and pwm_round_waveform_might_sleep()
+ */
+static inline bool pwmchip_supports_waveform(struct pwm_chip *chip)
+{
+	/*
+	 * only check for .write_waveform(). If that is available,
+	 * .round_waveform_tohw() and .round_waveform_fromhw() asserted to be
+	 * available, too, in pwmchip_add().
+	 */
+	return chip->ops->write_waveform != NULL;
+}
+
 static inline struct device *pwmchip_parent(const struct pwm_chip *chip)
 {
 	return chip->dev.parent;