PCI MSI: Add example request loop to MSI-HOWTO.txt
Encourage driver writers to think about supporting a variable number
of MSI-X interrupts, and give an example of how to do such a
request.
Acked-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
index 9494f6d..dcf7acc 100644
--- a/Documentation/PCI/MSI-HOWTO.txt
+++ b/Documentation/PCI/MSI-HOWTO.txt
@@ -176,7 +176,8 @@
If this function returns a negative number, it indicates an error and
the driver should not attempt to allocate any more MSI-X interrupts for
this device. If it returns a positive number, it indicates the maximum
-number of interrupt vectors that could have been allocated.
+number of interrupt vectors that could have been allocated. See example
+below.
This function, in contrast with pci_enable_msi(), does not adjust
dev->irq. The device will not generate interrupts for this interrupt
@@ -187,6 +188,26 @@
Device drivers should normally call this function once per device
during the initialization phase.
+It is ideal if drivers can cope with a variable number of MSI-X interrupts,
+there are many reasons why the platform may not be able to provide the
+exact number a driver asks for.
+
+A request loop to achieve that might look like:
+
+static int foo_driver_enable_msix(struct foo_adapter *adapter, int nvec)
+{
+ while (nvec >= FOO_DRIVER_MINIMUM_NVEC) {
+ rc = pci_enable_msix(adapter->pdev,
+ adapter->msix_entries, nvec);
+ if (rc > 0)
+ nvec = rc;
+ else
+ return rc;
+ }
+
+ return -ENOSPC;
+}
+
4.3.2 pci_disable_msix
void pci_disable_msix(struct pci_dev *dev)
