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PCI/MSI: Add pci_msi_vec_count()

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Device drivers can use this interface to obtain the maximum number of MSI
interrupts the device supports and use that number, e.g., in a subsequent
call to pci_enable_msi_block().

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Alexander Gordeev
2013-12-30 08:28:13 +01:00
committed by Bjorn Helgaas
parent 52179dc9ed
commit d1ac1d2622
3 changed files with 54 additions and 8 deletions
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15
Documentation/PCI/MSI-HOWTO.txt
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@@ -169,6 +169,21 @@ on any interrupt for which it previously called request_irq().
Failure to do so results in a BUG_ON(), leaving the device with
MSI enabled and thus leaking its vector.
4.2.5 pci_msi_vec_count
int pci_msi_vec_count(struct pci_dev *dev)
This function could be used to retrieve the number of MSI vectors the
device requested (via the Multiple Message Capable register). The MSI
specification only allows the returned value to be a power of two,
up to a maximum of 2^5 (32).
If this function returns a negative number, it indicates the device is
not capable of sending MSIs.
If this function returns a positive number, it indicates the maximum
number of MSI interrupt vectors that could be allocated.
4.3 Using MSI-X
The MSI-X capability is much more flexible than the MSI capability.