Re: [PATCH 5/7] I/OAT: Add support for MSI and MSI-X

[Roland Dreier]

 > Both igb (recently posted) and ixgbe (also recently posted) support both
 > MSI and MSI-X.  Right now when we try to request MSI-X vectors, if we
 > fail to acquire what we've asked for, we fall back to MSI support.  If
 > MSI fails to initialize, we fall back to legacy interrupts.  So it needs
 > to be there in case MSI-X allocation fails for the NIC driver.

Hmm, I see I don't understand what this driver is doing.  What is a
"struct ioatdma_device"?  Is this driver requesting interrupts that
come from the NIC or the IOAT DMA engine?

Anyway, if the NICs support MSI-X, is there any chance of failing to
get one MSI-X vectors but then succeeding in getting MSI enabled?
How could that happen?  I don't see what falling back to MSI buys you
beyond more code.

 - R.
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