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Subject: Re: [PATCH v2 0/4] Add extra pci roots support for Arm
To: Ard Biesheuvel <ard.biesheuvel@arm.com>, Jiahui Cen
 <cenjiahui@huawei.com>, devel@edk2.groups.io
Cc: jordan.l.justen@intel.com, leif@nuviainc.com, xieyingtai@huawei.com,
 miaoyubo@huawei.com
References: <20201109130511.5946-1-cenjiahui@huawei.com>
 <bb4c43a9-455d-aaba-37f4-a6874eb5ac51@arm.com>
From: "Laszlo Ersek" <lersek@redhat.com>
Message-ID: <286c4d14-82f4-6238-2fb1-15e6072fad07@redhat.com>
Date: Fri, 13 Nov 2020 20:44:16 +0100
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On 11/12/20 09:49, Ard Biesheuvel wrote:
> On 11/9/20 2:05 PM, Jiahui Cen wrote:
>> Changes with v1
>> v1->v2:
>> Separated into four patches.
>> Factor the same logic parts into a new library.
>>
>> v1: https://edk2.groups.io/g/devel/topic/72723351#56901
>> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3059
>> QEMU:
>> https://lore.kernel.org/qemu-devel/20201103120157.2286-1-cenjiahui@huawei.com/
>>
>>
>> This patch series adds support for extra pci roots for ARM.
>>
> 
> Why?

I don't know Jiahui Cen's particular reasons; on x86, pxb-pcie is useful
for associating PCIe hierarchies with particular NUMA nodes. See
"docs/pci_expander_bridge.txt" in the QEMU tree.

Also, in Jiahui Cen's QEMU blurb linked above, the following is included:

> Currently pxb-pcie is not supported by arm,
> the reason for it is pxb-pcie is not described in DSDT table
> and only one main host bridge is described in acpi tables,
> which means it is not impossible to present different io numas
> for different devices.

So I guess this work aims to extend the same PCI(e)<->NUMA association
feature, from x86 to ARM.

Thanks,
Laszlo