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PCI MSI: Add example request loop to MSI-HOWTO.txt

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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>
This commit is contained in:
Michael Ellerman 2009-03-20 15:22:12 +11:00 committed by Jesse Barnes
parent 5546d6f568
commit fafad5bf06
1 changed files with 22 additions and 1 deletions
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23
Documentation/PCI/MSI-HOWTO.txt
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@ -176,7 +176,8 @@ request_irq() for each 'vector' that it decides to use.
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 @@ free them again later.
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)