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Re: [Xen-devel] RFC: [PATCH 1/3] Enhance platform support for PCI

>>> On 27.02.15 at 16:24, <ian.campbell@xxxxxxxxxx> wrote:
> On Fri, 2015-02-27 at 14:54 +0000, Stefano Stabellini wrote:
>> MMCFG is a Linux config option, not to be confused with
>> PHYSDEVOP_pci_mmcfg_reserved that is a Xen hypercall interface.  I don't
>> think that the way Linux (or FreeBSD) call PHYSDEVOP_pci_mmcfg_reserved
>> is relevant.
> My (possibly flawed) understanding was that pci_mmcfg_reserved was
> intended to propagate the result of dom0 parsing some firmware table or
> other to the hypevisor.

That's not flawed at all.

> In Linux dom0 we call it walking pci_mmcfg_list, which looking at
> arch/x86/pci/mmconfig-shared.c pci_parse_mcfg is populated by walking
> over a "struct acpi_table_mcfg" (there also appears to be a bunch of
> processor family derived entries, which I guess are "quirks" of some
> sort).

Right - this parses ACPI tables (plus applies some knowledge about
certain specific systems/chipsets/CPUs) and verifies that the space
needed for the MMCFG region is properly reserved either in E820 or
in the ACPI specified resources (only if so Linux decides to use
MMCFG and consequently also tells Xen that it may use it).


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