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authorChristoph Hellwig <hch@lst.de>2017-02-15 08:58:22 +0100
committerBjorn Helgaas <bhelgaas@google.com>2017-02-15 10:32:57 -0600
commitc3cf2c61ddc1410424da0ea87717edf16fc296c5 (patch)
treefe2a895e44148f40772eb392ff94a64e62e0469e /Documentation/PCI
parent948b7620c15411444167a62cfc14cdd4b0e44682 (diff)
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PCI/MSI: Document pci_alloc_irq_vectors(), deprecate pci_enable_msi()
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>
Diffstat (limited to 'Documentation/PCI')
-rw-r--r--Documentation/PCI/pci.txt24
1 files changed, 12 insertions, 12 deletions
diff --git a/Documentation/PCI/pci.txt b/Documentation/PCI/pci.txt
index 77f49dc5be23..611a75e4366e 100644
--- a/Documentation/PCI/pci.txt
+++ b/Documentation/PCI/pci.txt
@@ -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.
-
-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().
+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.
+
+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.