linux-kernel - Re: [Patch v3] apple-gmux: lock iGP IO to protect from vgaarb changes

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Date:	Mon, 1 Jun 2015 19:31:58 +0200
From:	Darren Hart <dvhart@...radead.org>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	Michael Marineau <michael.marineau@...eos.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	platform-driver-x86@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Petri Hodju <petrihodju@...oo.com>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [Patch v3] apple-gmux: lock iGP IO to protect from vgaarb changes

On Mon, Jun 01, 2015 at 08:22:27AM +0200, Bruno Prémont wrote:
> On Fri, 29 May 2015 18:36:50 +0200 Darren Hart wrote:
> > > Making sure to lock only the intel GPU when present and especially protecting
> > > against nvidia driver will be hard if legacy-IO is being processed by a hidden
> > > device!
> > 
> > Ugh indeed. Worst case we can special case via dmi strings. Is this Apple device
> > significantly different from others? Bruno, what are you testing on?
> 
> I only own a pretty old MacBook Air with just NVIDIA IGP and had to
> rely on BUG reports and testing from affected users.
> 
> Not doing anything on apple-gmux when only a single GPU is visible
> should be easy, but denying any vgaarb operation when Intel IGP is
> hidden and just discrete GPU present is much harder (if one does not
> want to risk opening the next can of worms).
> 
> DMI based special-casing would work but will it uncover the next issue
> with the same device configured differently?

No, we would need a combination. I presume "configured differently" would mean
the Intel GPU present - which would be detectable.

DMI + Nvidia = do A
DMI + Intel = do B

-- 
Darren Hart
Intel Open Source Technology Center
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