Messages in this thread | | | Date | Thu, 1 Jul 2004 11:53:40 -0700 | From | Rajesh Shah <> | Subject | Re: MSI to memory? |
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On Thu, Jul 01, 2004 at 12:15:59PM -0600, Bjorn Helgaas wrote: > The conventional use of MSI is for a PCI adapter to generate processor > interrupts by writing to a local APIC. But I've seen some things
On Intel architecture at least, the MSI writes are targeted to the chipset (north bridge), not directly to a local APIC. The chipset knows the special MSI address and data values programmed into the PCI device and interprets the data written, e.g. for interrupt redirection hints.
> If so, is that a useful capability that should be exposed through > the Linux MSI interface?
With MSI, you get a single address/data pair. So MSI interrupts won't work unless this single entry is programmed to the special interrupt specific values that the chipset expects. With MSI-X, you get multiple address/data pairs but this is presumably because the device thinks it can benefit from multiple interrupts.
What type of usage model did you have in mind to have the device write to memory instead of using MSI for interrupts?
Rajesh
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