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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        David Vrabel <dvrabel@cantab.net>,
        Shannon Zhao <shannon.zhao@linaro.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        xen-devel <xen-devel@lists.xenproject.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [Xen-devel] [GIT PULL] xen: features and fixes for 4.8-rc0
Date: Thu, 28 Jul 2016 01:09:06 +0200
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On Wednesday, July 27, 2016 07:57:34 PM Andrew Cooper wrote:
> On 27/07/16 19:42, Linus Torvalds wrote:
> > On Wed, Jul 27, 2016 at 6:45 AM, David Vrabel <dvrabel@cantab.net> wrote:
> >> Shannon Zhao (16):
> >>       Xen: ACPI: Hide UART used by Xen
> > So this caused a trivial conflict. No biggie, it wasn't bad and the
> > patch was acked by Rafael. However, looking at it made me somewhat
> > unhappy.
> >
> > Should the device entry in ACPI really be hidden unconditionally? In
> > particular, if we are *not* running under virtualization, it sounds
> > wrong to hide it.
> >
> > Comments? Am I missing something?
> 
> The purpose of the ACPI STAO table (Status Override table, ratified in
> ACPI 6.0) is to list items elsewhere in the ACPI namespace which should
> be completely ignored.  It is used in cases where it is impossible or
> prohibitive to edit the system AML.
> 
> The patch itself only hides the UART if instructed to do so by the STAO
> table (last hunk).

Right.

The STAO definition document:

http://wiki.xenproject.org/mediawiki/images/0/02/Status-override-table.pdf

requires as to "operate as if that device does not exist", quite literally.

Thanks,
Rafael