counter: interrupt-cnt: Implement watch_validate callback

The interrupt-cnt counter driver only pushes one type of event on only
one channel: COUNTER_EVENT_CHANGE_OF_STATE on channel 0. The
interrupt_cnt_watch_validate() watch_valid callback is implemented to
ensure watch configurations are valid for this driver.

Cc: Oleksij Rempel <linux@rempel-privat.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Link: https://lore.kernel.org/r/20220815225058.144203-1-william.gray@linaro.org/Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Link: https://lore.kernel.org/r/c50b5eede7d3f523de8dc3937dc44680f2773e1d.1664318353.git.william.gray@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/counter/interrupt-cnt.c

@@ -139,12 +139,23 @@ static int interrupt_cnt_signal_read(struct counter_device *counter,
 	return 0;
 }
 
+static int interrupt_cnt_watch_validate(struct counter_device *counter,
+					const struct counter_watch *watch)
+{
+	if (watch->channel != 0 ||
+	    watch->event != COUNTER_EVENT_CHANGE_OF_STATE)
+		return -EINVAL;
+
+	return 0;
+}
+
 static const struct counter_ops interrupt_cnt_ops = {
 	.action_read = interrupt_cnt_action_read,
 	.count_read = interrupt_cnt_read,
 	.count_write = interrupt_cnt_write,
 	.function_read = interrupt_cnt_function_read,
 	.signal_read  = interrupt_cnt_signal_read,
+	.watch_validate  = interrupt_cnt_watch_validate,
 };
 
 static int interrupt_cnt_probe(struct platform_device *pdev)