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    SubjectRe: Multiple MSI
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    On Mon, 2008-07-07 at 10:17 -0600, Grant Grundler wrote:
    > On Thu, Jul 03, 2008 at 01:24:29PM +1000, Benjamin Herrenschmidt wrote:
    > ...
    > > > Next, MSI requires that you assign a block of interrupts that is a power
    > > > of two in size (between 2^0 and 2^5), and aligned to at least that power
    > > > of two.
    > ...
    > > > One thing I do want to be clear in the API is that the driver can ask
    > > > for any number of irqs, the pci layer will round up to the next power of
    > > > two if necessary.
    > >
    > > Well, that's where I'm not happy. The API shouldn't expose the
    > > "power-of-two" thing. The numbers shown to drivers aren't in the same
    > > space as the source numbers as seen by the HW on many architectures and
    > > thus don't need to have the same constraints.
    >
    > The drivers have to deal with the limitations of the HW spec.
    > In this case it means they have to know they are getting power of 2
    > number of interrupts. I think exposing this in the API is a requirement
    > and not optional.

    I don't think it's quite that strong. If a driver asked for 6 interrupts
    the MSI code could setup 8 and have 2 just hooked to nothing. I'm not
    sure that's a good idea, but it's possible.

    cheers

    --
    Michael Ellerman
    OzLabs, IBM Australia Development Lab

    email: michaele@au.ibm.com
    stime: ellerman@au1.ibm.com
    notes: Michael Ellerman/Australia/IBM
    phone: +61 2 6212 1183 (tie line 70 21183)

    We do not inherit the earth from our ancestors,
    we borrow it from our children. - S.M.A.R.T Person



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