firmware: arm_scmi: Track number of inflight SCMI transfers

Add a new debug counter, `XFERS_INFLIGHT`, to track the number of
currently active in-flight SCMI message transfers. This helps in
understanding system behavior and diagnosing potential issues with
pending or stuck messages.

The counter is incremented when a transfer is registered as in-flight,
and decremented when it completes and is released.

It is automatically added to debugfs for visibility through SCMI debugfs.

Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Philip Radford <philip.radford@arm.com>
Message-Id: <20250630105544.531723-3-philip.radford@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

Author: philAndTedsExcellentAdventure

drivers/firmware/arm_scmi/common.h

@@ -305,6 +305,7 @@ enum debug_counters {
 	ERR_MSG_INVALID,
 	ERR_MSG_NOMEM,
 	ERR_PROTOCOL,
+	XFERS_INFLIGHT,
 	SCMI_DEBUG_COUNTERS_LAST
 };
 

drivers/firmware/arm_scmi/driver.c

@@ -190,6 +190,7 @@ struct scmi_info {
 };
 
 #define handle_to_scmi_info(h)	container_of(h, struct scmi_info, handle)
+#define tx_minfo_to_scmi_info(h) container_of(h, struct scmi_info, tx_minfo)
 #define bus_nb_to_scmi_info(nb)	container_of(nb, struct scmi_info, bus_nb)
 #define req_nb_to_scmi_info(nb)	container_of(nb, struct scmi_info, dev_req_nb)
 
@@ -603,9 +604,14 @@ static inline void
 scmi_xfer_inflight_register_unlocked(struct scmi_xfer *xfer,
 				     struct scmi_xfers_info *minfo)
 {
+	/* In this context minfo will be tx_minfo due to the xfer pending */
+	struct scmi_info *info = tx_minfo_to_scmi_info(minfo);
+
 	/* Set in-flight */
 	set_bit(xfer->hdr.seq, minfo->xfer_alloc_table);
 	hash_add(minfo->pending_xfers, &xfer->node, xfer->hdr.seq);
+	scmi_inc_count(info->dbg->counters, XFERS_INFLIGHT);
+
 	xfer->pending = true;
 }
 
@@ -807,9 +813,13 @@ __scmi_xfer_put(struct scmi_xfers_info *minfo, struct scmi_xfer *xfer)
 	spin_lock_irqsave(&minfo->xfer_lock, flags);
 	if (refcount_dec_and_test(&xfer->users)) {
 		if (xfer->pending) {
+			struct scmi_info *info = tx_minfo_to_scmi_info(minfo);
+
 			scmi_xfer_token_clear(minfo, xfer);
 			hash_del(&xfer->node);
 			xfer->pending = false;
+
+			scmi_dec_count(info->dbg->counters, XFERS_INFLIGHT);
 		}
 		hlist_add_head(&xfer->node, &minfo->free_xfers);
 	}
@@ -2912,6 +2922,7 @@ static const char * const dbg_counter_strs[] = {
 	"err_msg_invalid",
 	"err_msg_nomem",
 	"err_protocol",
+	"xfers_inflight",
 };
 
 static ssize_t reset_all_on_write(struct file *filp, const char __user *buf,