Index: b/drivers/pci/msi.c
===================================================================
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -532,7 +532,7 @@ static int populate_msi_sysfs(struct pci
 }
 
 static struct msi_desc *
-msi_setup_entry(struct pci_dev *dev, int nvec, const struct irq_affinity *affd)
+msi_setup_entry(struct pci_dev *dev, int nvec, struct irq_affinity *affd)
 {
 	struct irq_affinity_desc *masks = NULL;
 	struct msi_desc *entry;
@@ -597,7 +597,7 @@ static int msi_verify_entries(struct pci
  * which could have been allocated.
  */
 static int msi_capability_init(struct pci_dev *dev, int nvec,
-			       const struct irq_affinity *affd)
+			       struct irq_affinity *affd)
 {
 	struct msi_desc *entry;
 	int ret;
@@ -669,7 +669,7 @@ static void __iomem *msix_map_region(str
 
 static int msix_setup_entries(struct pci_dev *dev, void __iomem *base,
 			      struct msix_entry *entries, int nvec,
-			      const struct irq_affinity *affd)
+			      struct irq_affinity *affd)
 {
 	struct irq_affinity_desc *curmsk, *masks = NULL;
 	struct msi_desc *entry;
@@ -736,7 +736,7 @@ static void msix_program_entries(struct
  * requested MSI-X entries with allocated irqs or non-zero for otherwise.
  **/
 static int msix_capability_init(struct pci_dev *dev, struct msix_entry *entries,
-				int nvec, const struct irq_affinity *affd)
+				int nvec, struct irq_affinity *affd)
 {
 	int ret;
 	u16 control;
@@ -932,7 +932,7 @@ int pci_msix_vec_count(struct pci_dev *d
 EXPORT_SYMBOL(pci_msix_vec_count);
 
 static int __pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries,
-			     int nvec, const struct irq_affinity *affd)
+			     int nvec, struct irq_affinity *affd)
 {
 	int nr_entries;
 	int i, j;
@@ -1018,7 +1018,7 @@ int pci_msi_enabled(void)
 EXPORT_SYMBOL(pci_msi_enabled);
 
 static int __pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec,
-				  const struct irq_affinity *affd)
+				  struct irq_affinity *affd)
 {
 	int nvec;
 	int rc;
@@ -1086,7 +1086,7 @@ EXPORT_SYMBOL(pci_enable_msi);
 
 static int __pci_enable_msix_range(struct pci_dev *dev,
 				   struct msix_entry *entries, int minvec,
-				   int maxvec, const struct irq_affinity *affd)
+				   int maxvec, struct irq_affinity *affd)
 {
 	int rc, nvec = maxvec;
 
@@ -1165,9 +1165,9 @@ EXPORT_SYMBOL(pci_enable_msix_range);
  */
 int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 				   unsigned int max_vecs, unsigned int flags,
-				   const struct irq_affinity *affd)
+				   struct irq_affinity *affd)
 {
-	static const struct irq_affinity msi_default_affd;
+	struct irq_affinity msi_default_affd = {0};
 	int msix_vecs = -ENOSPC;
 	int msi_vecs = -ENOSPC;
 
@@ -1196,6 +1196,13 @@ int pci_alloc_irq_vectors_affinity(struc
 	/* use legacy irq if allowed */
 	if (flags & PCI_IRQ_LEGACY) {
 		if (min_vecs == 1 && dev->irq) {
+			/*
+			 * Invoke the affinity spreading logic to ensure that
+			 * the device driver can adjust queue configuration
+			 * for the single interrupt case.
+			 */
+			if (affd)
+				irq_create_affinity_masks(1, affd);
 			pci_intx(dev, 1);
 			return 1;
 		}
Index: b/drivers/scsi/be2iscsi/be_main.c
===================================================================
--- a/drivers/scsi/be2iscsi/be_main.c
+++ b/drivers/scsi/be2iscsi/be_main.c
@@ -3566,7 +3566,7 @@ static void be2iscsi_enable_msix(struct
 
 	/* if eqid_count == 1 fall back to INTX */
 	if (enable_msix && nvec > 1) {
-		const struct irq_affinity desc = { .post_vectors = 1 };
+		struct irq_affinity desc = { .post_vectors = 1 };
 
 		if (pci_alloc_irq_vectors_affinity(phba->pcidev, 2, nvec,
 				PCI_IRQ_MSIX | PCI_IRQ_AFFINITY, &desc) < 0) {
Index: b/include/linux/interrupt.h
===================================================================
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -252,12 +252,18 @@ struct irq_affinity_notify {
  * @nr_sets:		The number of interrupt sets for which affinity
  *			spreading is required
  * @set_size:		Array holding the size of each interrupt set
+ * @calc_sets:		Callback for calculating the number and size
+ *			of interrupt sets
+ * @priv:		Private data for usage by @calc_sets, usually a
+ *			pointer to driver/device specific data.
  */
 struct irq_affinity {
 	unsigned int	pre_vectors;
 	unsigned int	post_vectors;
 	unsigned int	nr_sets;
 	unsigned int	set_size[IRQ_AFFINITY_MAX_SETS];
+	void		(*calc_sets)(struct irq_affinity *, unsigned int nvecs);
+	void		*priv;
 };
 
 /**
@@ -317,7 +323,7 @@ extern int
 irq_set_affinity_notifier(unsigned int irq, struct irq_affinity_notify *notify);
 
 struct irq_affinity_desc *
-irq_create_affinity_masks(unsigned int nvec, const struct irq_affinity *affd);
+irq_create_affinity_masks(unsigned int nvec, struct irq_affinity *affd);
 
 unsigned int irq_calc_affinity_vectors(unsigned int minvec, unsigned int maxvec,
 				       const struct irq_affinity *affd);
@@ -354,7 +360,7 @@ irq_set_affinity_notifier(unsigned int i
 }
 
 static inline struct irq_affinity_desc *
-irq_create_affinity_masks(unsigned int nvec, const struct irq_affinity *affd)
+irq_create_affinity_masks(unsigned int nvec, struct irq_affinity *affd)
 {
 	return NULL;
 }
Index: b/include/linux/pci.h
===================================================================
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1393,7 +1393,7 @@ static inline int pci_enable_msix_exact(
 }
 int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 				   unsigned int max_vecs, unsigned int flags,
-				   const struct irq_affinity *affd);
+				   struct irq_affinity *affd);
 
 void pci_free_irq_vectors(struct pci_dev *dev);
 int pci_irq_vector(struct pci_dev *dev, unsigned int nr);
@@ -1419,7 +1419,7 @@ static inline int pci_enable_msix_exact(
 static inline int
 pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
 			       unsigned int max_vecs, unsigned int flags,
-			       const struct irq_affinity *aff_desc)
+			       struct irq_affinity *aff_desc)
 {
 	if ((flags & PCI_IRQ_LEGACY) && min_vecs == 1 && dev->irq)
 		return 1;
Index: b/kernel/irq/affinity.c
===================================================================
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -230,6 +230,12 @@ static int irq_build_affinity_masks(cons
 	return ret;
 }
 
+static void default_calc_sets(struct irq_affinity *affd, unsigned int affvecs)
+{
+	affd->nr_sets = 1;
+	affd->set_size[0] = affvecs;
+}
+
 /**
  * irq_create_affinity_masks - Create affinity masks for multiqueue spreading
  * @nvecs:	The total number of vectors
@@ -240,20 +246,46 @@ static int irq_build_affinity_masks(cons
 struct irq_affinity_desc *
 irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
 {
-	unsigned int affvecs, curvec, usedvecs, nr_sets, i;
-	unsigned int set_size[IRQ_AFFINITY_MAX_SETS];
+	unsigned int affvecs, curvec, usedvecs, i;
 	struct irq_affinity_desc *masks = NULL;
 
 	/*
-	 * If there aren't any vectors left after applying the pre/post
-	 * vectors don't bother with assigning affinity.
+	 * Determine the number of vectors which need interrupt affinities
+	 * assigned. If the pre/post request exhausts the available vectors
+	 * then nothing to do here except for invoking the calc_sets()
+	 * callback so the device driver can adjust to the situation. If there
+	 * is only a single vector, then managing the queue is pointless as
+	 * well.
 	 */
-	if (nvecs == affd->pre_vectors + affd->post_vectors)
-		return NULL;
+	if (nvecs > 1 && nvecs > affd->pre_vectors + affd->post_vectors)
+		affvecs = nvecs - affd->pre_vectors - affd->post_vectors;
+	else
+		affvecs = 0;
+
+	/*
+	 * Simple invocations do not provide a calc_sets() callback. Install
+	 * the generic one. The check for affd->nr_sets is a temporary
+	 * workaround and will be removed after the NVME driver is converted
+	 * over.
+	 */
+	if (!affd->nr_sets && !affd->calc_sets)
+		affd->calc_sets = default_calc_sets;
+
+	/*
+	 * If the device driver provided a calc_sets() callback let it
+	 * recalculate the number of sets and their size. The check will go
+	 * away once the NVME driver is converted over.
+	 */
+	if (affd->calc_sets)
+		affd->calc_sets(affd, affvecs);
 
 	if (WARN_ON_ONCE(affd->nr_sets > IRQ_AFFINITY_MAX_SETS))
 		return NULL;
 
+	/* Nothing to assign? */
+	if (!affvecs)
+		return NULL;
+
 	masks = kcalloc(nvecs, sizeof(*masks), GFP_KERNEL);
 	if (!masks)
 		return NULL;
@@ -261,21 +293,13 @@ irq_create_affinity_masks(unsigned int n
 	/* Fill out vectors at the beginning that don't need affinity */
 	for (curvec = 0; curvec < affd->pre_vectors; curvec++)
 		cpumask_copy(&masks[curvec].mask, irq_default_affinity);
+
 	/*
 	 * Spread on present CPUs starting from affd->pre_vectors. If we
 	 * have multiple sets, build each sets affinity mask separately.
 	 */
-	affvecs = nvecs - affd->pre_vectors - affd->post_vectors;
-	nr_sets = affd->nr_sets;
-	if (!nr_sets) {
-		nr_sets = 1;
-		set_size[0] = affvecs;
-	} else {
-		memcpy(set_size, affd->set_size, nr_sets * sizeof(unsigned int));
-	}
-
-	for (i = 0, usedvecs = 0; i < nr_sets; i++) {
-		unsigned int this_vecs = set_size[i];
+	for (i = 0, usedvecs = 0; i < affd->nr_sets; i++) {
+		unsigned int this_vecs = affd->set_size[i];
 		int ret;
 
 		ret = irq_build_affinity_masks(affd, curvec, this_vecs,
@@ -318,7 +342,9 @@ unsigned int irq_calc_affinity_vectors(u
 	if (resv > minvec)
 		return 0;
 
-	if (affd->nr_sets) {
+	if (affd->calc_sets) {
+		set_vecs = maxvec - resv;
+	} else if (affd->nr_sets) {
 		unsigned int i;
 
 		for (i = 0, set_vecs = 0;  i < affd->nr_sets; i++)
