Re: [Xen-devel] [PATCH 3/3] x86/AMD-Vi: Fix IVRS HPET special->handle override

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.09.13 at 01:26, Suravee Suthikulanit <suravee.suthikulpanit@xxxxxxx> 
>>> wrote:
> Ok, after looking into Intel HPET specification, I can see that the spec 
> allows a particular system
> to have multiple HPETs.  And Jan was correct that only one is required 
> to be listed in the APCI HPET table.
> The rest are listed in ACPI namespace.
> 
> I look at the "arch/x86/hpet.c" and saw that this supports discovery in 
> the ACPI HPET table.
> However, there is only one "hpet_address" and "hpet_blockid", which are 
> initialized in the
> "arch/x86/acpi/boot.c: acpi_parse_hpet()".  If the code were to support 
> more than one HPET,
> this would have to be changed also.  Do you expect these to change as well?

This second paragraph contradicts what you correctly describe in
the first: There's only one required to be listed in the ACPI HPET
table, and hence that code isn't expected to change.

> Also, I don't see the code that would walk the ACPI namespace anywhere.  
> Does it exist?

In Dom0, yes. But the information not getting passed down is of
no relevance here: All we care about is how to correctly find the
IOMMU for the one HPET we use, which ought to work no matter
how many HPETs there are in the system.

Jan


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