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Subject: Re: [PATCH 2/4] x86/amd_nb: add support for newer PCI topologies
From: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>, "Woods, Brian" <Brian.Woods@amd.com>,
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Date: Wed, 07 Nov 2018 15:30:52 -0800
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[...]

> Sure, you can't *force* OEMs to supply a given ACPI device, but you
> can certainly say "if you want this functionality, supply INT3401
> devices."  That's what you do with PNP0A03 (PCI host bridges), for
> example.  If an OEM doesn't supply PNP0A03 devices, the system can
> boot just fine as long as you don't need PCI.
> 
> This model of using the PCI IDs forces OS vendors to release updates
> for every new platform.  I guess you must have considered that and
> decided whatever benefit you're getting was worth the cost.

Not worth cost. This is a pain. Every release we end up adding a single
line change to many drivers adding a PCI device id. 
Since there is no unique class_mask for PCI device for these devices,
we need to add device_id for each generation even if there is no
change.
Instead if we have some feature to say don't enumerate for PCI device
id < X and a black list, it will save lot of work.

Thanks,
Srinivas