Index: sys/dev/pci/pci.c
===================================================================
--- sys/dev/pci/pci.c
+++ sys/dev/pci/pci.c
@@ -1670,6 +1670,10 @@
 
 	KASSERT(msix->msix_msgnum > index, ("bogus index"));
 	offset = msix->msix_table_offset + index * 16 + 12;
+	/*
+	 * Some devices (eg Samsung PM961) cannot handle RMW on this register for
+	 * all its vectors write the values we need directly.
+	 */
 	bus_write_4(msix->msix_table_res, offset, PCIM_MSIX_VCTRL_MASK);
 }
 
@@ -1682,6 +1686,10 @@
 
 	KASSERT(msix->msix_table_len > index, ("bogus index"));
 	offset = msix->msix_table_offset + index * 16 + 12;
+	/*
+	 * Some devices (eg Samsung PM961) cannot handle RMW on this register for
+	 * all its vectors write the values we need directly.
+	 */
 	bus_write_4(msix->msix_table_res, offset, 0);
 }