[lkml]   [2008]   [Nov]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [PATCH 30 of 38] xen: implement io_apic_ops
    Eric W. Biederman wrote:
    > Jeremy Fitzhardinge <> writes:
    >> Ingo Molnar wrote:
    >>> * Jeremy Fitzhardinge <> wrote:
    >>>> Writes to the IO APIC are paravirtualized via hypercalls, so implement
    >>>> the appropriate operations.
    >>>> Signed-off-by: Jeremy Fitzhardinge <>
    >>>> ---
    >>>> arch/x86/xen/Makefile | 3 +-
    >>>> arch/x86/xen/apic.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++
    >>>> arch/x86/xen/enlighten.c | 2 +
    >>>> arch/x86/xen/xen-ops.h | 2 +
    >>>> 4 files changed, 72 insertions(+), 1 deletion(-)
    >>> hm, why is the ioapic used as the API here, and not an irqchip?
    >> In essence, the purpose of the series is to break the 1:1 relationship between
    >> Linux irqs and hardware GSIs.
    > Bad idea (I think). We have a 1:1 relationship between the linux irq number and
    > the GSI because it makes the code dramatically simpler, and it took significant
    > work to get there. The concept of an intermediate mapping layer sounds nasty.
    > But I haven't yet read the patch.

    The changes are spread over a number of patches, but the meat of it is
    in "xen: route hardware irqs via Xen". It turns out fairly simply, but
    perhaps its because I've made a number of simplifying assumptions:
    interrupts are always IOAPIC based, only using ACPI for routing, no MSI
    support yet.

    But it seems to me that the only time you really care that the irq isn't
    a gsi is when programming a vector into the ioapics - you need to do a
    irq -> ioapic/pin mapping anyway, so adding a irq -> gsi -> ioapic/pin
    map isn't all that complex. And conversely, when probing devices you
    need to map gsi->irq to see whether the interrupt is shared, though you
    could do that on a pure gsi level anyway.

    And of course the current code isn't purely irq == gsi anyway, since
    msis are allocated irqs as well, and there's no underlying gsi. In a
    sense you can think of the other Xen interrupt sources as being a bit
    like MSI, at least in as much as they're not sourced from a GSI (but
    they go further and are not sourced from an IOAPIC at all).


     \ /
      Last update: 2008-11-20 22:35    [W:0.023 / U:47.588 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site