linux-kernel - Re: [PATCH] ACPI: Disable ASPM if the platform won't provide

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Message-Id: <201006222042.14774.rjw@sisk.pl>
Date:	Tue, 22 Jun 2010 20:42:14 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Matthew Garrett <mjg@...hat.com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI: Disable ASPM if the platform won't provide _OSC control for PCIe

On Tuesday, June 22, 2010, Jesse Barnes wrote:
> On Tue, 22 Jun 2010 20:17:29 +0200
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > On Tuesday, June 22, 2010, Matthew Garrett wrote:
> > > The PCI SIG documentation for the _OSC OS/firmware handshaking interface
> > > states:
> > > 
> > > "If the _OSC control method is absent from the scope of a host bridge
> > > device, then the operating system must not enable or attempt to use any
> > > features defined in this section for the hierarchy originated by the host
> > > bridge."
> > > 
> > > The obvious interpretation of this is that the OS should not attempt to use
> > > PCIe hotplug, PME or AER - however, the specification also notes that an
> > > _OSC method is *required* for PCIe hierarchies, and experimental validation
> > > with An Alternative OS indicates that it doesn't use any PCIe functionality
> > > if the _OSC method is missing. That arguably means we shouldn't be using
> > > MSI or extended config space, but right now our problems seem to be limited
> > > to vendors being surprised when ASPM gets enabled on machines when other
> > > OSs refuse to do so. So, for now, let's just disable ASPM if the _OSC
> > > method doesn't exist or refuses to hand over PCIe capability control.
> > > 
> > > Signed-off-by: Matthew Garrett <mjg@...hat.com>
> > 
> > Acked-by: Rafael J. Wysocki <rjw@...k.pl>
> 
> Applied to my linux-next branch, thanks.

I think it's 2.6.35 (and probably -stable) material, these problems aleady
happen in the field.

Matthew, what do you think?

Rafael
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