counter: microchip-tcb-capture: Add watch validation support

The Timer Counter Block (TCB) exposes several kinds of events to the
Counter framework, but not every event is meaningful on every hardware
channel. Add a `watch_validate()` callback so userspace may register only
the combinations actually supported:

* Channel 0 (COUNTER_MCHP_EVCHN_CV, COUNTER_MCHP_EVCHN_RA)
   - COUNTER_EVENT_CAPTURE
   - COUNTER_EVENT_CHANGE_OF_STATE
   - COUNTER_EVENT_OVERFLOW

* Channel 1 (COUNTER_MCHP_EVCHN_RB)
   - COUNTER_EVENT_CAPTURE

* Channel 2 (COUNTER_MCHP_EVCHN_RC)
   - COUNTER_EVENT_THRESHOLD

Any other request is rejected with `-EINVAL`.

Signed-off-by: Dharma Balasubiramani <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: William Breathitt Gray <[email protected]>

Author: Dharma-B

drivers/counter/microchip-tcb-capture.c

@@ -337,6 +337,28 @@ static struct counter_comp mchp_tc_count_ext[] = {
 	COUNTER_COMP_COMPARE(mchp_tc_count_compare_read, mchp_tc_count_compare_write),
 };
 
+static int mchp_tc_watch_validate(struct counter_device *counter,
+				  const struct counter_watch *watch)
+{
+	if (watch->channel == COUNTER_MCHP_EVCHN_CV || watch->channel == COUNTER_MCHP_EVCHN_RA)
+		switch (watch->event) {
+		case COUNTER_EVENT_CHANGE_OF_STATE:
+		case COUNTER_EVENT_OVERFLOW:
+		case COUNTER_EVENT_CAPTURE:
+			return 0;
+		default:
+			return -EINVAL;
+		}
+
+	if (watch->channel == COUNTER_MCHP_EVCHN_RB && watch->event == COUNTER_EVENT_CAPTURE)
+		return 0;
+
+	if (watch->channel == COUNTER_MCHP_EVCHN_RC && watch->event == COUNTER_EVENT_THRESHOLD)
+		return 0;
+
+	return -EINVAL;
+}
+
 static struct counter_count mchp_tc_counts[] = {
 	{
 		.id = 0,
@@ -356,7 +378,8 @@ static const struct counter_ops mchp_tc_ops = {
 	.function_read  = mchp_tc_count_function_read,
 	.function_write = mchp_tc_count_function_write,
 	.action_read    = mchp_tc_count_action_read,
-	.action_write   = mchp_tc_count_action_write
+	.action_write   = mchp_tc_count_action_write,
+	.watch_validate = mchp_tc_watch_validate,
 };
 
 static const struct atmel_tcb_config tcb_rm9200_config = {