Re: [Xen-devel] [PATCH] AMD IOMMU: Support IOAPIC IDs larger than 128

[Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>]

Hi Jan,

On 12/01/2016 06:58 PM, Jan Beulich wrote:
> > > > On 01.12.16 at 12:04, <suravee.suthikulpanit@xxxxxxx> wrote:
> > Currently, the driver uses the APIC ID to index into the ioapic_sbdf array.
> > The current MAX_IO_APICS is 128, which causes the driver initialization
> > to fail on the system with IOAPIC ID >= 128.
> >
> > Instead, this patch adds APIC ID in the struct ioapic_sbdf,
> > which is used to match the entry when searching through the array.
> Wouldn't it have been a lot simpler to just bump the array size to
> 256? I'll comment on the rest of the patch anyway ...
Yes, it would, and that's what I originally tried. However, I was 
thinking that it would be unnecessarily waste of space since that would 
affect serveral structures i.e.
    * mp_ioapic_routing[MAX_IO_APICS]
    * mp_ioapics[MAX_IO_APICS]
    * nr_ioapic_entries[MAX_IO_APICS]
    * vector_map[MAX_IO_APICS]
    * ioapic_sbdf[MAX_IO_APICS]

If you think this is a reasonable change, I can simplify the patch. The 
number 256 should be reasonable for x1APIC since it only supports 8-bit 
APIC ID. However, this might be an issue later on with 32-bit APIC ID w/ 
x2APIC.
Thanks,
Suravee

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