linux-kernel - Re: [PATCH V4 2/2] PCI: vmd: Override ASPM on TGL/ADL VMD devices

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Message-ID: <YcLYz0x5oawOEHnI@infradead.org>
Date:   Tue, 21 Dec 2021 23:50:39 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     "David E. Box" <david.e.box@...ux.intel.com>
Cc:     Rajat Jain <rajatja@...gle.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        francisco.munoz.ruiz@...ux.intel.com, nirmal.patel@...ux.intel.com,
        jonathan.derrick@...ux.dev, lorenzo.pieralisi@....com,
        hch@...radead.org, kw@...ux.com, robh@...nel.org,
        bhelgaas@...gle.com, michael.a.bottini@...ux.intel.com,
        rafael@...nel.org, me@...ityamohan.in, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 2/2] PCI: vmd: Override ASPM on TGL/ADL VMD devices

On Tue, Dec 21, 2021 at 01:11:26PM -0800, David E. Box wrote:
> The reason why BIOS is not programming these values is because when VMD is
> enabled the ports are not visible to BIOS. This would apply to any BIOS
> including those used by ChromeOS.
> And because BIOS doesn't see these ports ...

Isn't VMD enabled by the BIOS?  The bios should be able see them the
same way as Linux does.  But given that the whole point of VMD is to hide 
these ports from Windows it obviously doesn't.  For Linux and thus for
ChromeOS VMD is completely pointless, so give that the ChromeOS people
aren't as dumb as some people at Intel I'm pretty sure they won't enable
it and just use the ports as normal one and avoid this whole
self-inflicted pain.

If only Intel could give the OS a way to disable VMD at runtime and
discover the actual ports, then we would not have this whole nightmare
of having to support it.