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

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Message-ID: <Z78uOaPESGXWN46M@gmail.com>
Date: Wed, 26 Feb 2025 16:07:37 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Rostyslav Khudolii <ros@...c.com>
Cc: Yazen Ghannam <yazen.ghannam@....com>, 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


* Rostyslav Khudolii <ros@...c.com> wrote:

> > My understanding, based on the above info, is that ACPI should be 
> > used. The direct register enablement is still possible for 
> > backwards compatibility, if needed.
> >
> > I think your observation proves a good point. The registers were 
> > moved starting in Zen. But this is not an issue on modern OSes 
> > since ACPI is used by default.
> 
> This is my understanding too. However, what is the desired behavior 
> on Zen if the CONFIG_ACPI_MCFG and CONFIG_PCI_MMCONFIG are both 
> disabled? ECS should not be possible since the registers were moved, 
> right? If that's the case then, at the very least, it would be great 
> to have a warning message.
>
> > For your specific issue, I think we should determine if there is a 
> > configuration or a firmware problem.
> 
> To give a bit more context: I am porting the kernel which works on 
> the AMD Ryzen™ Embedded V1000-based device. On that system, it seems 
> like the firmware doesn't disable IO access to ECS (which is wrong), 
> hence we have never experienced this issue before. Now, the 
> R2000-based device's firmware disables IO access to ECS (correctly) 
> and that's when the issue starts to happen.

[ Sorry about the late reply. ]

So what is the practical impact here? Do things start breaking 
unexpectedly if CONFIG_ACPI_MCFG and CONFIG_PCI_MMCONFIG are disabled? 
Then I'd suggest fixing that in the Kconfig space, either by adding a 
dependency on ACPI_MCFG && PCI_MMCONFIG, or by selecting those 
must-have pieces of infrastructure.

Thanks,

	Ingo