Re: [Xen-devel] [PATCH][HVM] fix PCI interrupt routing via ACPI

["Dave Lively" <dave.lively@xxxxxxxxx>]

I like the simplification.

What about PIC mode support?  OSes expecting just a PIC may
rely on being able to choose the 4 PCI IRQs.  But I don't know
this for sure.  In fact, I remember Win2003 with the ACPI PIC HAL
was successfully working around this problem (by leaving the PCI
IRQ assignments unchanged), though it complained in the event
log.  I'm not sure whether we can rely on this or not ...

Also, I worry in general about deviating too much from emulation
of existing chipsets (at least for anything required at guest OS 
install time).  Surprising a guest with (perfectly legitimate) combinations
of hardware it hasn't seen before can be dangerous.

Dave

On 10/14/06, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:

Or, could we simply:
 1. throw away the PCI-ISA bridge device (from qemu and from the ACPI DSDT)
 2. throw away the legacy '$PIR' routing table in rombios.c
 3. initialise the IRQ field of each PCI device config space to sane unique values
 4. Make ACPI PRTP static and match the values chosen in (3).
 5. Also throw away all the LNK stuff from ACPI DSDT

If we're allowed to do this (programmable PCI-ISA bridge isn't part of MP or ACPI specs, for example) then this seems to involve throwing away a load of tedious code and thus removing an IRQ-mapping bottleneck. No drawbacks, unless I'm ignorant of some PC architectural detail (quite possible)?

 -- Keir

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