linux-kernel - Re: PCI IO ECS access is no longer possible for AMD family 17h

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Message-ID: <CAJDH93u+9KLBVSrFnQm3==9E4VaVohavq+FZT+UqWdRs9FHn-g@mail.gmail.com>
Date: Tue, 4 Mar 2025 08:39:29 +0100
From: Rostyslav Khudolii <ros@...c.com>
To: Yazen Ghannam <yazen.ghannam@....com>
Cc: Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, x86@...nel.org, 
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>, "tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: PCI IO ECS access is no longer possible for AMD family 17h

Hi Yazen,

>
> Ros,
> Is/was there a reason why you didn't have the MCFG/MMCONFIG options
> enabled in your kernel?
>
> Was this a side effect of trying to build a minimal kernel or similar?
>
> Thanks,
> Yazen
>
> P.S. Sorry for the late reply. My mailbox is missing Ros's reply to me.

I inherited a kernel config used here from a previous custom,
V1000-based solution. Most likely originally
it came from the x86_64_defconfig. Maybe MMCONFIG wasn't enabled by
default at that time.
We never had problems with this because our BIOS keeps the IO ECS
enabled (that's against the spec recommendation).
The kernel default for PCI_MMCONFIG is 'y' now, so it's unlikely that
people will run into this issue unless
they explicitly disable it.

Regards,
Rostyslav