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

William Breathitt Gray
2025-05-18T07:41:39Z

[-- Attachment #1: Type: text/plain, Size: 3540 bytes --]

On Thu, May 15, 2025 at 10:28:25AM +0530, Dharma Balasubiramani wrote:
> Introduce a watch validation callback to restrict supported event and
> channel combinations. This allows userspace to receive notifications only
> for valid event types and sources. Specifically, enable the following
> supported events on channels RA, RB, and RC:
>
> - COUNTER_EVENT_CAPTURE
> - COUNTER_EVENT_CHANGE_OF_STATE
> - COUNTER_EVENT_OVERFLOW
> - COUNTER_EVENT_THRESHOLD
>
> Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>
> ---
> drivers/counter/microchip-tcb-capture.c | 28 +++++++++++++++++++++++++---
> 1 file changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/counter/microchip-tcb-capture.c b/drivers/counter/microchip-tcb-capture.c
> index 1de3c50b9804..179ff5595143 100644
> --- a/drivers/counter/microchip-tcb-capture.c
> +++ b/drivers/counter/microchip-tcb-capture.c
> @@ -337,6 +337,27 @@ 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)
> +{
> + switch (watch->channel) {
> + case COUNTER_MCHP_EVCHN_RA:
> + case COUNTER_MCHP_EVCHN_RB:
> + case COUNTER_MCHP_EVCHN_RC:

Hello Dharma,

Include COUNTER_MCHP_EVCHN_CV as well for the sake of completeness. I
know COUNTER_MCHP_EVCHN_CV and COUNTER_MCHP_EVCHN_RA have the same
underlying channel id, but we're abstracting this fact so it's good to
maintain the consistency of the abstraction across all callbacks.

> + switch (watch->event) {
> + case COUNTER_EVENT_CAPTURE:
> + case COUNTER_EVENT_CHANGE_OF_STATE:
> + case COUNTER_EVENT_OVERFLOW:
> + case COUNTER_EVENT_THRESHOLD:
> + return 0;

The watch_validate callback is used to ensure that the requested watch
configuration is valid: i.e. the watch event is appropriate for the
watch channel.

Looking at include/uapi/linux/counter/microchip-tcb-capture.h:

* Channel 0:
* - CV register changed
* - CV overflowed
* - RA captured
* Channel 1:
* - RB captured
* Channel 2:
* - RC compare triggered

If I'm understanding correctly, channel 0 supports only the
CHANGE_OF_STATE, OVERFLOW, and CAPTURE events; channel 1 supports only
CAPTURE events; and channel 2 supports only THRESHOLD events.

Adjust the code to ensure those limitations.

> + default:
> + return -EINVAL;
> + }
> + default:
> + return -EINVAL;
> + }
> +}
> +
> static struct counter_count mchp_tc_counts[] = {
> {
> .id = 0,
> @@ -351,12 +372,13 @@ static struct counter_count mchp_tc_counts[] = {
> };
>
> static const struct counter_ops mchp_tc_ops = {
> - .signal_read = mchp_tc_count_signal_read,
> + .action_read = mchp_tc_count_action_read,
> + .action_write = mchp_tc_count_action_write,
> .count_read = mchp_tc_count_read,
> .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
> + .signal_read = mchp_tc_count_signal_read,

It's nice to alphabetize the counter_ops callbacks, but it's also
unrelated to the watch_validate implementation. Move the alphabetization
cleanup to a separate patch so that this patch remains dedicated to
just watch_validate changes.

Thanks,

William Breathitt Gray

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]