pwm: Let pwm_set_waveform_might_sleep() fail for exact but impossible requests

Up to now pwm_set_waveform_might_sleep() returned 1 for exact requests
that couldn't be served exactly. In contrast to
pwm_round_waveform_might_sleep() and pwm_set_waveform_might_sleep() with
exact = false this is an error condition. So simplify handling for
callers of pwm_set_waveform_might_sleep() by returning -EDOM instead of
1 in this case.

Signed-off-by: Uwe Kleine-König <[email protected]>
Link: https://lore.kernel.org/r/20538a46719584dafd8a1395c886780a97dcdf79.1746010245.git.u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <[email protected]>

Author: ukleinek

drivers/pwm/core.c

@@ -404,15 +404,16 @@ static int __pwm_set_waveform(struct pwm_device *pwm,
  * Typically a requested waveform cannot be implemented exactly, e.g. because
  * you requested .period_length_ns = 100 ns, but the hardware can only set
  * periods that are a multiple of 8.5 ns. With that hardware passing @exact =
- * true results in pwm_set_waveform_might_sleep() failing and returning 1. If
- * @exact = false you get a period of 93.5 ns (i.e. the biggest period not bigger
- * than the requested value).
+ * true results in pwm_set_waveform_might_sleep() failing and returning -EDOM.
+ * If @exact = false you get a period of 93.5 ns (i.e. the biggest period not
+ * bigger than the requested value).
  * Note that even with @exact = true, some rounding by less than 1 ns is
  * possible/needed. In the above example requesting .period_length_ns = 94 and
  * @exact = true, you get the hardware configured with period = 93.5 ns.
  *
- * Returns: 0 on success, 1 if was rounded up (if !@exact) or no perfect match was
- * possible (if @exact), or a negative errno
+ * Returns: 0 on success, 1 if was rounded up (if !@exact), -EDOM if setting
+ * failed due to the exact waveform not being possible (if @exact), or a
+ * different negative errno on failure.
  * Context: May sleep.
  */
 int pwm_set_waveform_might_sleep(struct pwm_device *pwm,
@@ -440,6 +441,16 @@ int pwm_set_waveform_might_sleep(struct pwm_device *pwm,
 		err = __pwm_set_waveform(pwm, wf, exact);
 	}
 
+	/*
+	 * map err == 1 to -EDOM for exact requests. Also make sure that -EDOM is
+	 * only returned in exactly that case. Note that __pwm_set_waveform()
+	 * should never return -EDOM which justifies the unlikely().
+	 */
+	if (unlikely(err == -EDOM))
+		err = -EINVAL;
+	else if (exact && err == 1)
+		err = -EDOM;
+
 	return err;
 }
 EXPORT_SYMBOL_GPL(pwm_set_waveform_might_sleep);