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authorAlexander Gordeev <agordeev@redhat.com>2013-05-13 09:05:48 (GMT)
committerBjorn Helgaas <bhelgaas@google.com>2013-05-28 17:31:16 (GMT)
commit65f6ae66a6fb44f614a1226c398fcb38e94b3c59 (patch)
tree15c6f443e875f85c6194936adb26959dfa6cf685 /COPYING
parentf722406faae2d073cc1d01063d1123c35425939e (diff)
downloadlinux-65f6ae66a6fb44f614a1226c398fcb38e94b3c59.tar.xz
PCI: Allocate only as many MSI vectors as requested by driver
Because of the encoding of the "Multiple Message Capable" and "Multiple Message Enable" fields, a device can only advertise that it's capable of a power-of-two number of vectors, and the OS can only enable a power-of-two number. For example, a device that's limited internally to using 18 vectors would have to advertise that it's capable of 32. The 14 extra vectors consume vector numbers and IRQ descriptors even though the device can't actually use them. This fix introduces a 'msi_desc::nvec_used' field to address this issue. When non-zero, it is the actual number of MSIs the device will send, as requested by the device driver. This value should be used by architectures to set up and tear down only as many interrupt resources as the device will actually use. Note, although the existing 'msi_desc::multiple' field might seem redundant, in fact it is not. The number of MSIs advertised need not be the smallest power-of-two larger than the number of MSIs the device will send. Thus, it is not always possible to derive the former from the latter, so we need to keep them both to handle this case. [bhelgaas: changelog, rename to "nvec_used"] Signed-off-by: Alexander Gordeev <agordeev@redhat.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
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