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PCI/MSI: Document pci_alloc_irq_vectors(), deprecate pci_enable_msi()

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Document pci_alloc_irq_vectors() instead of the deprecated pci_enable_msi()
and pci_enable_msix() APIs.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
This commit is contained in:
Christoph Hellwig 2017-02-15 08:58:22 +01:00 committed by Bjorn Helgaas
parent 948b7620c1
commit c3cf2c61dd
1 changed files with 11 additions and 11 deletions
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22
Documentation/PCI/pci.txt
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@ -382,18 +382,18 @@ The fundamental difference between MSI and MSI-X is how multiple
"vectors" get allocated. MSI requires contiguous blocks of vectors
while MSI-X can allocate several individual ones.
MSI capability can be enabled by calling pci_enable_msi() or
pci_enable_msix() before calling request_irq(). This causes
the PCI support to program CPU vector data into the PCI device
capability registers.
MSI capability can be enabled by calling pci_alloc_irq_vectors() with the
PCI_IRQ_MSI and/or PCI_IRQ_MSIX flags before calling request_irq(). This
causes the PCI support to program CPU vector data into the PCI device
capability registers. Many architectures, chip-sets, or BIOSes do NOT
support MSI or MSI-X and a call to pci_alloc_irq_vectors with just
the PCI_IRQ_MSI and PCI_IRQ_MSIX flags will fail, so try to always
specify PCI_IRQ_LEGACY as well.
If your PCI device supports both, try to enable MSI-X first.
Only one can be enabled at a time. Many architectures, chip-sets,
or BIOSes do NOT support MSI or MSI-X and the call to pci_enable_msi/msix
will fail. This is important to note since many drivers have
two (or more) interrupt handlers: one for MSI/MSI-X and another for IRQs.
They choose which handler to register with request_irq() based on the
return value from pci_enable_msi/msix().
Drivers that have different interrupt handlers for MSI/MSI-X and
legacy INTx should chose the right one based on the msi_enabled
and msix_enabled flags in the pci_dev structure after calling
pci_alloc_irq_vectors.
There are (at least) two really good reasons for using MSI:
1) MSI is an exclusive interrupt vector by definition.