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    SubjectRe: PCI: MSI interrupts masked using prohibited method
    Date
    On Friday, July 25, 2008 9:56 am Matthew Wilcox wrote:
    > On Fri, Jul 25, 2008 at 05:37:49PM +0100, David Vrabel wrote:
    > > The spec says that system software should enable MSI before setting
    > > message address and data (PCI 3.0 section 6.8.3.1 MSI configuration).
    > > The kernel doesn't do this.
    >
    > I think you meant "disable"? I can't find anything in 6.8.3.1 of 3.0
    > that refers to this.
    >
    > > I really don't think we should be enabling/disabling MSI while
    > > interrupts might be being generated. There are cases where interrupts
    > > will be lost. Consider PCIe where we might end up with a situation
    > > where MSI is disabled and then enabled sufficiently quickly that no
    > > periodic line interrupt message is sent by the device.
    >
    > I don't think there's a difference here between PCIe and conventional
    > PCI. A device raising a line based interrupt is perfectly equivalent to
    > a device sending an INTx message.
    >
    > > The message address and data should only be modified while the vector is
    > > masked (to avoid the aforementioned 'tearing'). This means that setting
    > > IRQ affinity cannot be done on devices without per-vector mask bits. I
    > > don't think this is a problem.
    >
    > I agree. I think it's fine to have this limitation.
    >
    > > In vague psuedo-code, set_affinity() should be something like this:
    > >
    > > int did_mask = msi_mask_vector();
    > > if (!did_mask) {
    > > return -ENOTSUPP;
    > > }
    > > /* fiddle with address and mask now */
    > > msi_unmask_vector();
    >
    > Yes, something like that.

    Yeah, that reflects what we actually support...

    David, can you resend your "don't mask MSIs using the MSI enable bit" patch
    against the latest bits so I can apply it? Did you also want to hack up the
    above for the affinity code?

    Thanks,
    Jesse


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