[PATCH v3] counter: microchip-tcb-capture: Add watch validation support

[PATCH v3] counter: microchip-tcb-capture: Add watch validation support

[Dharma Balasubiramani]

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>
---
Tested the code on target (sam9x60_curiosity) using the following commands

valid ones:
./counter_watch_events -d -wevt_change_of_state,chan=0
./counter_watch_events -d -wevt_ovf,chan=0
./counter_watch_events -d -wevt_capture,chan=0
./counter_watch_events -d -wevt_capture,chan=1
./counter_watch_events -d -wevt_threshold,chan=2

invalid ones:
./counter_watch_events -d -wevt_threshold,chan=0
./counter_watch_events -d -wevt_threshold,chan=1
Error adding watches[0]: Invalid argument
---
Changes in v3:
- Update commit description to not mention undefined behaviour as that is
  not the case.
- Use the early returns to avoid the else statements and code consistent with
  linux style.
- Link to v2: https://lore.kernel.org/r/20250520-counter-tcb-v2-1-a0617d2d220a@microchip.com

Changes in v2:
- Include COUNTER_MCHP_EVCHN_CV as well for the sake of completeness.
- Adjust the code to ensure channel limitations.
- Drop sorting in this patch, will be taken care seperately.
- Link to v1: https://lore.kernel.org/r/20250515-counter-tcb-v1-1-e547061ed80f@microchip.com
---
 drivers/counter/microchip-tcb-capture.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/counter/microchip-tcb-capture.c b/drivers/counter/microchip-tcb-capture.c
index 1de3c50b9804..1a299d1f350b 100644
--- 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 = {

---
base-commit: 8566fc3b96539e3235909d6bdda198e1282beaed
change-id: 20250515-counter-tcb-b6ae1945210b

Best regards,
-- 
Dharma Balasubiramani <dharma.b@microchip.com>

Re: [PATCH v3] counter: microchip-tcb-capture: Add watch validation support

[William Breathitt Gray]

On Tue, 20 May 2025 20:51:46 +0530, Dharma Balasubiramani wrote:
> 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
> 
> [...]

Applied, thanks!

[1/1] counter: microchip-tcb-capture: Add watch validation support
      commit: ae3392c0f12f179b969ce17856ed18bf8d69a35e

Best regards,
-- 
William Breathitt Gray <wbg@kernel.org>