PCI ECAM requirements

[jonmasters]

ECAM must be preserved in the face of OS re-enumeration of the PCI fabric. It should be noted that an OS/other SEE software may renumber downstream buses. When this happens, in an implementation composed from multiple independent root ports, it is necessary to ensure that the correct underlying fabric routing is preserved.

[mdchitale]

Could you please provide more background on this requirement, especially the part about multiple independent root ports?

[mdchitale]

Is this requirement similar to what is implemented in the linux kernel: https://elixir.bootlin.com/linux/latest/source/drivers/acpi/pci_root.c#L929

[jonmasters]

Alas, no. Linux has support for a platform to request that the configuration provided by firmware be preserved, but that cannot always be used, and other OSes require that the OS re-enumerate the PCI topology. Re-enumeration in the presence of disparate root port IP causes many integration challenges, such as needing to reconfigure the fabric underneath for routing. You'll want to have a comprehensive set of documentation covering all of these challenges.

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On Fri, Mar 25, 2022 at 12:18 AM mdchitale ***@***.***> wrote: Is this requirement similar to what is implemented in the linux kernel: https://elixir.bootlin.com/linux/latest/source/drivers/acpi/pci_root.c#L929 — Reply to this email directly, view it on GitHub <#81 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAATOZKSU56KAYWZ4CKE3ZTVBU5DFANCNFSM5Q7VWCXQ> . You are receiving this because you authored the thread.Message ID: ***@***.***>

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[kumarsankaran]

Merged. Thanks.