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

["Jaggi, Manish" <Manish.Jaggi@xxxxxxxxxx>]

Hi,

>On 16/12/2016 15:49, Julien Grall wrote:
>> On 14/12/16 08:00, Jiandi An wrote:
>>> 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?
>
>I thought a bit more about it and I realized we need to be cautious on 
>how to proceed here.
>
>DOM0 will have a mix of real devices and emulated devices (e.g some part 
>of the GIC). For the emulated devices, DOM0 should not call 
>XENMEM_add_to_physmap_range. However, DOM0 is not aware what is emulated 
>or not, so even the current approach (hooking up in platform device) 
>seems fragile. We rely on Xen to say "this region cannot be mapped".
>
 Why not add support for parsing ACPI tables in Xen, from linux,  as we parse 
dt.

-manish


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