Re: [Xen-devel] Xen: ARM: Support for mapping ECAM PCIe Config Space Specified In Static ACPI Table

[Julien Grall <julien.grall@xxxxxxx>]

On 14/12/16 08:00, Jiandi An wrote:
> Hi Guys,
Hello Jiandi,

> Xen currently doesn't map ECAM space specified in static ACPI table.
> Seeking opinion on how this should be handled properly.
> Each root complex ECAM region takes up 64K 4K pages (256MB).
> For some platforms there might be multiple root complexes.
> Is the plan to map all at once?Julien has mentioned support
> for mapping ECAM may come when support for PCI passthrough is
> added, is that right? What mechanism will it be? Will Xen or
> dom0 be the one that parses the staic ACPI tables and map the ECAM space?

For performance reason, each ECAM region would need to be mapped at 
once, so the stage-2 page table could take advantage of superpage (it 
will mostly be 2MB).
Now, I don't think Xen should map the ECAM region in stage-2 before 
hand. All the regions may not be described in the MCFG and I would like 
to see a generic solution.
Looking at the code (see pci_create_ecam_create in drivers/pci/ecam.c), 
ioremap is used. I believe the problem is the same for the 2 other 
threads you sent ( [1] and [2]).
So it might be good to look at hooking up a call to 
XENMEM_add_to_physmap_range in ioremap.
Any opinions?

Cheers,

[1] 
https://lists.xenproject.org/archives/html/xen-devel/2016-12/msg01693.html
[2] 
https://lists.xenproject.org/archives/html/xen-devel/2016-12/msg01737.html
--
Julien Grall

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