cxl: Rework error message for incompatible slots

Improve the error message shown if a capi adapter is plugged on a
capi-incompatible slot directly under the PHB (no intermediate switch).

Fixes: 56328743 ("cxl: Add support for POWER9 DD2")
Cc: stable@vger.kernel.org # 4.14+
Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200407115601.25453-1-fbarrat@linux.ibm.com

drivers/misc/cxl/pci.c

@@ -393,8 +393,8 @@ int cxl_calc_capp_routing(struct pci_dev *dev, u64 *chipid,
 	*capp_unit_id = get_capp_unit_id(np, *phb_index);
 	of_node_put(np);
 	if (!*capp_unit_id) {
-		pr_err("cxl: invalid capp unit id (phb_index: %d)\n",
-		       *phb_index);
+		pr_err("cxl: No capp unit found for PHB[%lld,%d]. Make sure the adapter is on a capi-compatible slot\n",
+		       *chipid, *phb_index);
 		return -ENODEV;
 	}