Re: [PATCH] rename CONFIG_PCI_USE_VECTOR to CONFIG_PCI_MSI

[Roland Dreier <roland@topspin.com>]

    Bjorn> Rename CONFIG_PCI_USE_VECTOR to CONFIG_PCI_MSI.  The
    Bjorn> "vector" terminology is architecture-dependent.  The PCI
    Bjorn> MSI interface actually deals with Linux IRQ numbers (i.e.,
    Bjorn> things you can pass to request_irq()), and we shouldn't
    Bjorn> confuse things by calling them "vectors" just because we're
    Bjorn> using MSI rather than an IOSAPIC.

Seems reasonable... however CONFIG_PCI_USE_VECTOR really has two
overloaded meanings (at least on i386).  First of all, as you say, it
does enable drivers to request MSI/MSI-X.  However, on i386
CONFIG_PCI_USE_VECTOR also changes how the APIC is setup (the most
visible effect of which is different interrupt numbers).

I would propose the following course of action:

 1) Merge Long's latest MSI/MSI-X patches (updated patches in
    http://gmane.linux.kernel/218830).  Without the new semantics of
    pci_disable_msi()/pci_disable_msix(), it's very difficult to use
    MSI/MSI-X in a device driver.
 2) Split the config options so we have an i386-specific
    CONFIG_PCI_USE_VECTOR and a generic CONFIG_PCI_MSI (with
    CONFIG_PCI_MSI depending on something like !I386 || CONFIG_PCI_USE_VECTOR)
    This would be an updated version of your patch.
 3) Make the code in drivers/pci/msi.c less Intel-specific -- instead
    of hard-coding Intel-specific addresses for vectors have the
    computation call into arch code.  This would be a fair amount of
    work and depends documentation for non-Intel platforms that
    implement MSI/MSI-X -- should be easier as PCI Express comes out.

 - Roland