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

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Message-ID: <20250304152614.GA1785630@yaz-khff2.amd.com>
Date: Tue, 4 Mar 2025 10:26:14 -0500
From: Yazen Ghannam <yazen.ghannam@....com>
To: Rostyslav Khudolii <ros@...c.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

On Tue, Mar 04, 2025 at 08:39:29AM +0100, Rostyslav Khudolii wrote:
> 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.
> 

Thanks Rostyslav for confirming.

This seems to be the commit:
55027a7772b1 ("x86: Align x86_64 PCI_MMCONFIG with 32-bit variant")

Before this, PCI_MMCONFIG was default 'y' on 32-bit and no default on
64-bit.

It has been default 'y' on 32-bit since the beginning of history.
1da177e4c3f4 ("Linux-2.6.12-rc2")

Thanks,
Yazen