bus: arm-ccn: Provide required event arguments

Since 688d4dfcdd "perf tools: Support
parsing parameterized events" the perf userspace tools understands
"argument=?" syntax in the events file, making sure that required
arguments are provided by the user and not defaulting to 0, causing
confusion.

This patch adds the required arguments lists for CCN events.

Signed-off-by: Pawel Moll <pawel.moll@arm.com>

drivers/bus/arm-ccn.c

@@ -340,6 +340,23 @@ static ssize_t arm_ccn_pmu_event_show(struct device *dev,
 	if (event->mask)
 		res += snprintf(buf + res, PAGE_SIZE - res, ",mask=0x%x",
 				event->mask);
+
+	/* Arguments required by an event */
+	switch (event->type) {
+	case CCN_TYPE_CYCLES:
+		break;
+	case CCN_TYPE_XP:
+		res += snprintf(buf + res, PAGE_SIZE - res,
+				",xp=?,port=?,vc=?,dir=?");
+		if (event->event == CCN_EVENT_WATCHPOINT)
+			res += snprintf(buf + res, PAGE_SIZE - res,
+					",cmp_l=?,cmp_h=?,mask=?");
+		break;
+	default:
+		res += snprintf(buf + res, PAGE_SIZE - res, ",node=?");
+		break;
+	}
+
 	res += snprintf(buf + res, PAGE_SIZE - res, "\n");
 
 	return res;