From 65f6ae66a6fb44f614a1226c398fcb38e94b3c59 Mon Sep 17 00:00:00 2001 From: Alexander Gordeev Date: Mon, 13 May 2013 11:05:48 +0200 Subject: 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 Signed-off-by: Bjorn Helgaas --- include/linux/msi.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/msi.h') diff --git a/include/linux/msi.h b/include/linux/msi.h index 20c2d6dd5d25..ee66f3a12fb6 100644 --- a/include/linux/msi.h +++ b/include/linux/msi.h @@ -35,6 +35,7 @@ struct msi_desc { u32 masked; /* mask bits */ unsigned int irq; + unsigned int nvec_used; /* number of messages */ struct list_head list; union { -- cgit v1.2.3-59-g8ed1b