PCI: Provide sensible IRQ vector alloc/free routines

Add a function to allocate and free a range of interrupt vectors, using
MSI-X, MSI or legacy vectors (in that order) based on the capabilities of
the underlying device and PCIe complex.

Additionally a new helper is provided to get the Linux IRQ number for given
device-relative vector so that the drivers don't need to allocate their own
arrays to keep track of the vectors for the multi vector MSI-X case.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alexander Gordeev <agordeev@redhat.com>

drivers/pci/msi.c

@@ -4,6 +4,7 @@
  *
  * Copyright (C) 2003-2004 Intel
  * Copyright (C) Tom Long Nguyen (tom.l.nguyen@intel.com)
+ * Copyright (C) 2016 Christoph Hellwig.
  */
 
 #include <linux/err.h>
@@ -1121,6 +1122,94 @@ int pci_enable_msix_range(struct pci_dev *dev, struct msix_entry *entries,
 }
 EXPORT_SYMBOL(pci_enable_msix_range);
 
+/**
+ * pci_alloc_irq_vectors - allocate multiple IRQs for a device
+ * @dev:		PCI device to operate on
+ * @min_vecs:		minimum number of vectors required (must be >= 1)
+ * @max_vecs:		maximum (desired) number of vectors
+ * @flags:		flags or quirks for the allocation
+ *
+ * Allocate up to @max_vecs interrupt vectors for @dev, using MSI-X or MSI
+ * vectors if available, and fall back to a single legacy vector
+ * if neither is available.  Return the number of vectors allocated,
+ * (which might be smaller than @max_vecs) if successful, or a negative
+ * error code on error. If less than @min_vecs interrupt vectors are
+ * available for @dev the function will fail with -ENOSPC.
+ *
+ * To get the Linux IRQ number used for a vector that can be passed to
+ * request_irq() use the pci_irq_vector() helper.
+ */
+int pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
+		unsigned int max_vecs, unsigned int flags)
+{
+	int vecs = -ENOSPC;
+
+	if (!(flags & PCI_IRQ_NOMSIX)) {
+		vecs = pci_enable_msix_range(dev, NULL, min_vecs, max_vecs);
+		if (vecs > 0)
+			return vecs;
+	}
+
+	if (!(flags & PCI_IRQ_NOMSI)) {
+		vecs = pci_enable_msi_range(dev, min_vecs, max_vecs);
+		if (vecs > 0)
+			return vecs;
+	}
+
+	/* use legacy irq if allowed */
+	if (!(flags & PCI_IRQ_NOLEGACY) && min_vecs == 1)
+		return 1;
+	return vecs;
+}
+EXPORT_SYMBOL(pci_alloc_irq_vectors);
+
+/**
+ * pci_free_irq_vectors - free previously allocated IRQs for a device
+ * @dev:		PCI device to operate on
+ *
+ * Undoes the allocations and enabling in pci_alloc_irq_vectors().
+ */
+void pci_free_irq_vectors(struct pci_dev *dev)
+{
+	pci_disable_msix(dev);
+	pci_disable_msi(dev);
+}
+EXPORT_SYMBOL(pci_free_irq_vectors);
+
+/**
+ * pci_irq_vector - return Linux IRQ number of a device vector
+ * @dev: PCI device to operate on
+ * @nr: device-relative interrupt vector index (0-based).
+ */
+int pci_irq_vector(struct pci_dev *dev, unsigned int nr)
+{
+	if (dev->msix_enabled) {
+		struct msi_desc *entry;
+		int i = 0;
+
+		for_each_pci_msi_entry(entry, dev) {
+			if (i == nr)
+				return entry->irq;
+			i++;
+		}
+		WARN_ON_ONCE(1);
+		return -EINVAL;
+	}
+
+	if (dev->msi_enabled) {
+		struct msi_desc *entry = first_pci_msi_entry(dev);
+
+		if (WARN_ON_ONCE(nr >= entry->nvec_used))
+			return -EINVAL;
+	} else {
+		if (WARN_ON_ONCE(nr > 0))
+			return -EINVAL;
+	}
+
+	return dev->irq + nr;
+}
+EXPORT_SYMBOL(pci_irq_vector);
+
 struct pci_dev *msi_desc_to_pci_dev(struct msi_desc *desc)
 {
 	return to_pci_dev(desc->dev);

include/linux/pci.h

@@ -1237,6 +1237,10 @@ resource_size_t pcibios_iov_resource_alignment(struct pci_dev *dev, int resno);
 int pci_set_vga_state(struct pci_dev *pdev, bool decode,
 		      unsigned int command_bits, u32 flags);
 
+#define PCI_IRQ_NOLEGACY	(1 << 0) /* don't use legacy interrupts */
+#define PCI_IRQ_NOMSI		(1 << 1) /* don't use MSI interrupts */
+#define PCI_IRQ_NOMSIX		(1 << 2) /* don't use MSI-X interrupts */
+
 /* kmem_cache style wrapper around pci_alloc_consistent() */
 
 #include <linux/pci-dma.h>
@@ -1284,6 +1288,11 @@ static inline int pci_enable_msix_exact(struct pci_dev *dev,
 		return rc;
 	return 0;
 }
+int pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
+		unsigned int max_vecs, unsigned int flags);
+void pci_free_irq_vectors(struct pci_dev *dev);
+int pci_irq_vector(struct pci_dev *dev, unsigned int nr);
+
 #else
 static inline int pci_msi_vec_count(struct pci_dev *dev) { return -ENOSYS; }
 static inline void pci_msi_shutdown(struct pci_dev *dev) { }
@@ -1307,6 +1316,24 @@ static inline int pci_enable_msix_range(struct pci_dev *dev,
 static inline int pci_enable_msix_exact(struct pci_dev *dev,
 		      struct msix_entry *entries, int nvec)
 { return -ENOSYS; }
+static inline int pci_alloc_irq_vectors(struct pci_dev *dev,
+		unsigned int min_vecs, unsigned int max_vecs,
+		unsigned int flags)
+{
+	if (min_vecs > 1)
+		return -EINVAL;
+	return 1;
+}
+static inline void pci_free_irq_vectors(struct pci_dev *dev)
+{
+}
+
+static inline int pci_irq_vector(struct pci_dev *dev, unsigned int nr)
+{
+	if (WARN_ON_ONCE(nr > 0))
+		return -EINVAL;
+	return dev->irq;
+}
 #endif
 
 #ifdef CONFIG_PCIEPORTBUS