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

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Date:	Wed, 18 Mar 2015 20:46:18 -0700
From:	Darren Hart <dvhart@...radead.org>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	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 Wed, Mar 11, 2015 at 10:34:45PM +0100, Bruno Prémont wrote:
> As GMUX depends on IO for iGP to be enabled and active, lock the IO at
> vgaarb level. This should prevent GPU driver for dGPU to disable IO for
> iGP while it tries to own legacy VGA IO.
> 
> This fixes usage of backlight control combined with closed nvidia
> driver on some Apple dual-GPU (intel/nvidia) systems.
> 
> On those systems loading nvidia driver disables intel IO decoding,
> disabling the gmux backlight controls as a side effect.
> Prior to commits moving boot_vga from (optional) efifb to less optional
> vgaarb this mis-behavior could be avoided by using right kernel config
> (efifb enabled but vgaarb disabled).
> 
> This patch explicitly does not try to trigger vgaarb changes in order
> to avoid confusing already running graphics drivers. If IO has been
> mis-configured by vgaarb gmux will thus fail to probe.
> It is expected to load/probe gmux prior to graphics drivers.
> 
> Fixes: ce027dac592c0ada241ce0f95ae65856828ac450 # nvidia interaction
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=86121
> Reported-by: Petri Hodju <petrihodju@...oo.com>
> Tested-by: Petri Hodju <petrihodju@...oo.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Matthew Garrett <matthew.garrett@...ula.com>
> Signed-off-by: Bruno Prémont <bonbons@...ux-vserver.org>
> ---
> Resending v2 in the hope Darren won't hit quoted-printable.
> Also adding linux-pci on CC by Bjorn's request in bugzilla.

Much better, thanks. Queued.

-- 
Darren Hart
Intel Open Source Technology Center
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