cxl: Add checks to access_coordinate calculation to fail missing data

Jonathan noted that when the coordinates for host bridge and switches
can be 0s if no actual data are retrieved and the calculation continues.
The resulting number would be inaccurate. Add checks to ensure that the
calculation would complete only if the numbers are valid.

While not seen in the wild, issue may show up with a BIOS that reported
CXL root ports via Generic Ports (via a PCI handle in the SRAT entry).

Fixes: 14a6960 ("cxl: Add helper function that calculate performance data for downstream ports")
Reported-by: Jonathan Cameron <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Davidlohr Bueso <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dave Jiang <[email protected]>

Author: davejiang

drivers/cxl/core/port.c

@@ -2141,6 +2141,18 @@ static void add_latency(struct access_coordinate *c, long latency)
 	}
 }
 
+static bool coordinates_valid(struct access_coordinate *c)
+{
+	for (int i = 0; i < ACCESS_COORDINATE_MAX; i++) {
+		if (c[i].read_bandwidth && c[i].write_bandwidth &&
+		    c[i].read_latency && c[i].write_latency)
+			continue;
+		return false;
+	}
+
+	return true;
+}
+
 static void set_min_bandwidth(struct access_coordinate *c, unsigned int bw)
 {
 	for (int i = 0; i < ACCESS_COORDINATE_MAX; i++) {
@@ -2206,13 +2218,18 @@ int cxl_endpoint_get_perf_coordinates(struct cxl_port *port,
 		 * There's no valid access_coordinate for a root port since RPs do not
 		 * have CDAT and therefore needs to be skipped.
 		 */
-		if (!is_cxl_root)
+		if (!is_cxl_root) {
+			if (!coordinates_valid(dport->coord))
+				return -EINVAL;
 			cxl_coordinates_combine(c, c, dport->coord);
+		}
 		add_latency(c, dport->link_latency);
 	} while (!is_cxl_root);
 
 	dport = iter->parent_dport;
 	/* Retrieve HB coords */
+	if (!coordinates_valid(dport->coord))
+		return -EINVAL;
 	cxl_coordinates_combine(c, c, dport->coord);
 
 	/* Get the calculated PCI paths bandwidth */