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Lukas Wunner 598b21708e Revert "apple-gmux: lock iGP IO to protect from vgaarb changes" 
commit d6fa7588fd upstream.

Commit 4eebd5a4e7 ("apple-gmux: lock iGP IO to protect from vgaarb
changes") amended this driver's ->probe hook to lock decoding of normal
(non-legacy) I/O space accesses to the integrated GPU on dual-GPU
MacBook Pros.  The lock stays in place until the driver is unbound.

The change was made to work around an issue with the out-of-tree nvidia
graphics driver (available at http://www.nvidia.com/object/unix.html).
It contains the following sequence in nvidia/nv.c:

	#if defined(CONFIG_VGA_ARB) && !defined(NVCPU_PPC64LE)
	#if defined(VGA_DEFAULT_DEVICE)
	    vga_tryget(VGA_DEFAULT_DEVICE, VGA_RSRC_LEGACY_MASK);
	#endif
	    vga_set_legacy_decoding(dev, VGA_RSRC_NONE);
	#endif

This code was reported to cause deadlocks with VFIO already in 2013:
https://devtalk.nvidia.com/default/topic/545560

I've reported the issue to Nvidia developers once more in 2017:
https://www.spinics.net/lists/dri-devel/msg138754.html

On the MacBookPro10,1, this code apparently breaks backlight control
(which is handled by apple-gmux via an I/O region starting at 0x700),
as reported by Petri Hodju:
https://bugzilla.kernel.org/show_bug.cgi?id=86121

I tried to replicate Petri's observations on my MacBook9,1, which uses
the same Intel Ivy Bridge + Nvidia GeForce GT 650M architecture, to no
avail.  On my machine apple-gmux' I/O region remains accessible even
with the nvidia driver loaded and commit 4eebd5a4e7 reverted.
Petri reported that apple-gmux becomes accessible again after a
suspend/resume cycle because the BIOS changed the VGA routing on the
root port to the Nvidia GPU.  Perhaps this is a BIOS issue after all
that can be fixed with an update?

In any case, the change made by commit 4eebd5a4e7 has turned out to
cause two new issues:

* Wilfried Klaebe reports a deadlock when launching Xorg because it
  opens /dev/vga_arbiter and calls vga_get(), but apple-gmux is holding
  a lock on I/O space indefinitely.  It looks like apple-gmux' current
  behavior is an abuse of the vgaarb API as locks are not meant to be
  held for longer periods:
  https://bugzilla.kernel.org/show_bug.cgi?id=88861#c11
  https://bugzilla.kernel.org/attachment.cgi?id=217541

* On dual GPU MacBook Pros introduced since 2013, the integrated GPU is
  powergated on boot und thus becomes invisible to Linux unless a custom
  EFI protocol is used to leave it powered on.  (A patch exists but is
  not in mainline yet due to several negative side effects.)  On these
  machines, locking I/O to the integrated GPU (as done by 4eebd5a4e7)
  fails and backlight control is therefore broken:
  https://bugzilla.kernel.org/show_bug.cgi?id=105051

So let's revert commit 4eebd5a4e7 please.  Users experiencing the
issue with the proprietary nvidia driver can comment out the above-
quoted problematic code as a workaround (or try updating the BIOS).

Cc: Petri Hodju <petrihodju@yahoo.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Bruno Prémont <bonbons@linux-vserver.org>
Cc: Andy Ritger <aritger@nvidia.com>
Cc: Ronald Tschalär <ronald@innovation.ch>
Tested-by: Wilfried Klaebe <linux-kernel@lebenslange-mailadresse.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2018-02-22 15:42:26 +01:00
arch arm64: Add missing Falkor part number for branch predictor hardening 2018-02-22 15:42:25 +01:00
block blk-mq: quiesce queue before freeing queue 2018-02-16 20:23:09 +01:00
certs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
crypto kmemcheck: stop using GFP_NOTRACK and SLAB_NOTRACK 2018-02-22 15:42:23 +01:00
Documentation kmemcheck: rip it out 2018-02-22 15:42:24 +01:00
drivers Revert "apple-gmux: lock iGP IO to protect from vgaarb changes" 2018-02-22 15:42:26 +01:00
firmware License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs mbcache: initialize entry->e_referenced in mb_cache_entry_create() 2018-02-22 15:42:25 +01:00
include mlx5: fix mlx5_get_vector_affinity to start from completion vector 0 2018-02-22 15:42:26 +01:00
init kmemcheck: stop using GFP_NOTRACK and SLAB_NOTRACK 2018-02-22 15:42:23 +01:00
ipc License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
kernel kmemcheck: rip it out 2018-02-22 15:42:24 +01:00
lib kmemcheck: rip it out 2018-02-22 15:42:24 +01:00
mm kmemcheck: rip it out for real 2018-02-22 15:42:24 +01:00
net kmemcheck: remove annotations 2018-02-22 15:42:23 +01:00
samples samples/bpf: adjust rlimit RLIMIT_MEMLOCK for xdp1 2017-12-20 10:10:31 +01:00
scripts kmemcheck: rip it out 2018-02-22 15:42:24 +01:00
security ima/policy: fix parsing of fsuuid 2018-02-03 17:38:53 +01:00
sound ASoC: skl: Fix kernel warning due to zero NHTL entry 2018-02-16 20:23:04 +01:00
tools selftests/x86/mpx: Fix incorrect bounds with old _sigfault 2018-02-22 15:42:24 +01:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: arm/arm64: Handle CPU_PM_ENTER_FAILED 2018-02-16 20:23:03 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: rpm-pkg: keep spec file until make mrproper 2018-02-13 10:19:46 +01:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING [PATCH] update FSF address in COPYING 2005-09-10 10:06:29 -07:00
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS kmemcheck: rip it out 2018-02-22 15:42:24 +01:00
Makefile Linux 4.14.20 2018-02-16 20:23:12 +01:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.