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 <dharma.b@microchip.com>
Link: https://lore.kernel.org/r/20250520-counter-tcb-v3-1-4631e2aff7ed@microchip.com
Signed-off-by: William Breathitt Gray <wbg@kernel.org>

diff --git a/drivers/counter/microchip-tcb-capture.c b/drivers/counter/microchip-tcb-capture.c
index 1de3c50b98043897b92a91c9cd78ec77e925326e..1a299d1f350b840dae1417571739ee07c6fb2659 100644 (file)
--- a/drivers/counter/microchip-tcb-capture.c
+++ 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 = {