linux-kernel - Re: [PATCH 1/2] x86/amd_node: Fix AMD root device caching

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Message-ID: <20251021142507.GA62725@yaz-khff2.amd.com>
Date: Tue, 21 Oct 2025 10:25:07 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Mario Limonciello <mario.limonciello@....com>,
	Filip Barczyk <filip.barczyk@...o.net>
Subject: Re: [PATCH 1/2] x86/amd_node: Fix AMD root device caching

On Tue, Oct 21, 2025 at 04:15:00PM +0200, Borislav Petkov wrote:
> On Tue, Oct 21, 2025 at 09:37:45AM -0400, Yazen Ghannam wrote:
> > It's correct that one of the root devices will be on bus 0x0. But that
> > device will be part of AMD node 0. So we still need to pick a root
> > device for the other, if any, AMD nodes in the system.
> > 
> > For example, a system with 2 AMD nodes could have this:
> > Node 0 : 0x00 0x07 0x0e 0x15
> > Node 1 : 0x1c 0x23 0x2a 0x31
> 
> Aha, so next question: isn't there a way to figure out which is the *first*
> PCI bus of a AMD node? My gut feeling tells me there should be some info
> somewhere which we can use...
> 

Yep, that was one of the goals of the recent rework. I thought the DF
register held that info, but I was mistaken.

I haven't been able to find anything else. We can keep looking, but I
wanted to send out this patch as a fix in the meantime.

Thanks,
Yazen