On Mon, Jul 04, 2016 at 05:39:28PM +0900, Christoph Hellwig wrote:

Add a function to allocate a range of interrupt vectors, which will
transparently use MSI-X and MSI if available or fallback to legacy
vectors.  The interrupts are available in a core managed array in the
pci_dev structure, and can also be released using a similar function.
A new helper, __pci_enable_msix_range, is introduced to allow allocating
the array of msix descriptors in the core PCIe code at the exact number
of vectors supported by the PCI host complex, and to also help with the
automatic IRQ affinity assignment that will be added in the next commit.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 Documentation/PCI/MSI-HOWTO.txt | 437 ++++------------------------------------

[...]

+ pci_enable_msi, pci_enable_msi_range, pci_enable_msi_exact, pci_disable_msi,
+ pci_msi_vec_count, pci_enable_msix_range, pci_enable_msix_exact,
+ pci_disable_msix, pci_msix_vec_count

Description of these functions can be removed when all drivers migrated
to the new API. Also implementation descriptions + examples would still
be needed AFAICT.

[...]

This function's code almost matches the existing pci_enable_msix_range()
so pci_enable_msix_range() should be reworked instead IMHO.

I took a look at the existing code and the rework does not appear
necessary as __pci_enable_msix_range() could look like this:

static int __pci_enable_msix_range(struct pci_dev *dev, unsigned int min_vecs,
		unsigned int max_vecs)
{
	int ret, i;
	struct msix_entry *entries;

	entries = kmalloc_array(max_vecs, sizeof(entries[0]), GFP_KERNEL);
	if (!entries)
		return -ENOMEM;

	for (i = 0; i < max_vecs; i++)
		entries[i].entry = i;

	ret = pci_enable_msix_range(dev, entries, min_vecs, max_vecs);

	kfree(entries);

	return ret;
}


We do not need to keep msix_entry array, since it only needed for
pci_irq_vector() function. But the same info could be retrieved from
msi_desc::irq.

+/**
+ * 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;
+
+	if (!(flags & PCI_IRQ_NOMSIX)) {
+		vecs = __pci_enable_msix_range(dev, 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 (min_vecs == 1)
+		return 1;
+	return -ENOSPC;

The original error code (in vecs) would be overridden with -ENOSPC here.

As suggested above, it is not needed.

So here you could search with for_each_pci_msi_entry() instead.

+	WARN_ON_ONCE(!dev->msi_enabled && nr > 0);
+	return dev->irq + nr;

I think this function should check irq number existence and return the
vector number or -EINVAL;

In case CONFIG_PCI_MSI is unset min_vecs > 1 is -EINVAL;

+	return 1;
+}
+static inline void pci_free_irq_vectors(struct pci_dev *dev)
+{
+}
+
+static inline unsigned int pci_irq_vector(struct pci_dev *dev, unsigned int nr)
+{
+	WARN_ON_ONCE(nr > 0);

As suggested above, it would rather -EINVAL;

+	return dev->irq;
+}
 #endif
 
 #ifdef CONFIG_PCIEPORTBUS
-- 
2.1.4