1 files changed, 40 insertions, 3 deletions

diff --git a/sys/dev/nvme/nvme_ctrlr.c b/sys/dev/nvme/nvme_ctrlr.c
index 22ba2a5..cf3b3b2 100644
--- a/sys/dev/nvme/nvme_ctrlr.c
+++ b/sys/dev/nvme/nvme_ctrlr.c
@@ -1075,8 +1075,8 @@ nvme_ctrlr_construct(struct nvme_controller *ctrlr, device_t dev)
 {
 	union cap_lo_register	cap_lo;
 	union cap_hi_register	cap_hi;
-	int			num_vectors, per_cpu_io_queues, status = 0;
-	int			timeout_period;
+	int			i, num_vectors, per_cpu_io_queues, rid;
+	int			status, timeout_period;
 
 	ctrlr->dev = dev;
 
@@ -1149,8 +1149,45 @@ nvme_ctrlr_construct(struct nvme_controller *ctrlr, device_t dev)
 		goto intx;
 	}
 
-	if (pci_alloc_msix(dev, &num_vectors) != 0)
+	if (pci_alloc_msix(dev, &num_vectors) != 0) {
 		ctrlr->msix_enabled = 0;
+		goto intx;
+	}
+
+	/*
+	 * On earlier FreeBSD releases, there are reports that
+	 *  pci_alloc_msix() can return successfully with all vectors
+	 *  requested, but a subsequent bus_alloc_resource_any()
+	 *  for one of those vectors fails.  This issue occurs more
+	 *  readily with multiple devices using per-CPU vectors.
+	 * To workaround this issue, try to allocate the resources now,
+	 *  and fall back to INTx if we cannot allocate all of them.
+	 *  This issue cannot be reproduced on more recent versions of
+	 *  FreeBSD which have increased the maximum number of MSI-X
+	 *  vectors, but adding the workaround makes it easier for
+	 *  vendors wishing to import this driver into kernels based on
+	 *  older versions of FreeBSD.
+	 */
+	for (i = 0; i < num_vectors; i++) {
+		rid = i + 1;
+		ctrlr->msi_res[i] = bus_alloc_resource_any(ctrlr->dev,
+		    SYS_RES_IRQ, &rid, RF_ACTIVE);
+
+		if (ctrlr->msi_res[i] == NULL) {
+			ctrlr->msix_enabled = 0;
+			while (i > 0) {
+				i--;
+				bus_release_resource(ctrlr->dev,
+				    SYS_RES_IRQ,
+				    rman_get_rid(ctrlr->msi_res[i]),
+				    ctrlr->msi_res[i]);
+			}
+			pci_release_msi(dev);
+			nvme_printf(ctrlr, "could not obtain all MSI-X "
+			    "resources, reverting to intx\n");
+			break;
+		}
+	}
 
 intx: