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    SubjectRe: [PATCH] x86/sfi: fix ioapic gsi range
    On Tue, 08 Jun 2010 14:22:18 -0700 (Eric W. Biederman) wrote:

    > jacob pan <> writes:
    > > On Tue, 08 Jun 2010 12:41:45 -0700
    > > (Eric W. Biederman) wrote:
    > >
    > >
    > >> Even if sfi is never implemented on a platform where that kind of
    > >> hardware exists, the current sfi code is setup to coexist
    > >> simultaneously in the kernel with all of the infrastructure of
    > >> other platforms where those kinds of devices exist. Which means
    > >> there can be drivers compiled into your kernel that make
    > >> assumptions about special properties of the irqs 0-15.
    > >>
    > > SFI code can be compiled in with ACPI at the same time but at
    > > runtime there is only one used, ACPI take precedence. So there
    > > wouldn't be any additional conflict caused by SFI added APIC tables.
    > >
    > >> As for the question about using legacy_pic to detect the absence of
    > >> an irq controller that Peter raised. We can't do that because it
    > >> should be possible for an acpi system with all of the legacy
    > >> hardware to exist without needing to implement an i8259, or ever
    > >> run in the historical interrupt delivery mode of pcs.
    > > In your case, I don't understand how would it change the
    > > calculation of irq mapping. Even if you don't use i8259 on a x86 PC
    > > platform, you still have NR_LEGACY_IRQS=legacy_pic->nr_legacy_irqs.
    > >
    > > On the other side, use NR_LEGACY_IRQS breaks the existing code for
    > > Moorestown in terms of irq-gsi lookup and nr_irqs_gsi.
    > Is this code merged where I should have fixed it in my patchset?
    yes, merged.
    > We went through this with acpi having an identity mapping of irq to
    > gsi mapping and the result is that we (a) developed weird platform
    > specific hooks for things that should have been handled by generic
    > code, and on other systems we lost access to 16 irqs.
    > It took probably 10 years to sort the acpi irq handling out. What
    > I have learned along the way is:
    > - Sharing irq in software is madness, so a one to one mapping with
    > hardware irq is required.
    > - An identity mapping with gsis is nice but we can't count on the
    > hardware designers or the spec designers always doing sane and
    > reasonable things so not guaranteeing a particular mapping is
    > important.
    > If I have actually broken any sfi drivers because you assumed a
    > particular we are back where we were with ISA, and still haven't
    > completely escaped. The abstraction layer should provide all of
    > the mapping so drivers only see linux irq numbers.
    > Eric

    [jacob pan]

    In arch/x86/kernel/mrst.c we parse SFI MTMR table then
    add timer irqs to mp_irqs. what is broken by this patch is
    pin_2_irq() lookup for the legacy irq range since we want
    NR_IRQS_LEGACY to be 0 on Moorestown. We do have the assumption that
    mp_irqs from SFI is 1:1 mapped to IRQs.

    Doing this can fix the problem, but you mentioned you have to use
    NR_IRQS_LEGACY, which i still don't understand.

    --- a/arch/x86/kernel/apic/io_apic.c
    +++ b/arch/x86/kernel/apic/io_apic.c
    @@ -1032,7 +1032,7 @@ static int pin_2_irq(int idx, int apic, int pin)
    } else {
    u32 gsi = mp_gsi_routing[apic].gsi_base + pin;

    - if (gsi >= NR_IRQS_LEGACY)
    + if (gsi >= legacy_pic->nr_legacy_irqs)
    irq = gsi;

    The second problem is nr_irqs_gsi gets an extra 16 for Moorestown.
    Similarly, we need this in probe_nr_irqs_gsi:
    - nr = gsi_top + NR_IRQS_LEGACY;
    + nr = gsi_top + legacy_pic->nr_legacy_irqs;

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