<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux.git/drivers/acpi/internal.h, branch v3.13</title>
<subtitle>Linux kernel source tree</subtitle>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/'/>
<entry>
<title>Merge branch 'acpi-hotplug'</title>
<updated>2013-11-07T18:31:15+00:00</updated>
<author>
<name>Rafael J. Wysocki</name>
<email>rafael.j.wysocki@intel.com</email>
</author>
<published>2013-11-07T18:31:15+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=63ff4d0765a4e30afa659edbf09006987fc62499'/>
<id>63ff4d0765a4e30afa659edbf09006987fc62499</id>
<content type='text'>
* acpi-hotplug:
  ACPI / hotplug: Consolidate deferred execution of ACPI hotplug routines
  ACPI / hotplug: Do not execute "insert in progress" _OST
  ACPI / hotplug: Carry out PCI root eject directly
  ACPI / hotplug: Merge device hot-removal routines
  ACPI / hotplug: Make acpi_bus_hot_remove_device() internal
  ACPI / hotplug: Simplify device ejection routines
  ACPI / hotplug: Fix handle_root_bridge_removal()
  ACPI / hotplug: Refuse to hot-remove all objects with disabled hotplug
  ACPI / scan: Start matching drivers after trying scan handlers
  ACPI: Remove acpi_pci_slot_init() headers from internal.h

Conflicts:
	include/acpi/acpiosxf.h (with the 'acpica' branch)
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
* acpi-hotplug:
  ACPI / hotplug: Consolidate deferred execution of ACPI hotplug routines
  ACPI / hotplug: Do not execute "insert in progress" _OST
  ACPI / hotplug: Carry out PCI root eject directly
  ACPI / hotplug: Merge device hot-removal routines
  ACPI / hotplug: Make acpi_bus_hot_remove_device() internal
  ACPI / hotplug: Simplify device ejection routines
  ACPI / hotplug: Fix handle_root_bridge_removal()
  ACPI / hotplug: Refuse to hot-remove all objects with disabled hotplug
  ACPI / scan: Start matching drivers after trying scan handlers
  ACPI: Remove acpi_pci_slot_init() headers from internal.h

Conflicts:
	include/acpi/acpiosxf.h (with the 'acpica' branch)
</pre>
</div>
</content>
</entry>
<entry>
<title>ACPI / hotplug: Consolidate deferred execution of ACPI hotplug routines</title>
<updated>2013-11-07T18:28:48+00:00</updated>
<author>
<name>Rafael J. Wysocki</name>
<email>rafael.j.wysocki@intel.com</email>
</author>
<published>2013-11-07T00:45:40+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=7b98118aaa5d75644c48f41fc5d0cc181e478383'/>
<id>7b98118aaa5d75644c48f41fc5d0cc181e478383</id>
<content type='text'>
There are two different interfaces for queuing up work items on the
ACPI hotplug workqueue, alloc_acpi_hp_work() used by PCI and PCI host
bridge hotplug code and acpi_os_hotplug_execute() used by the common
ACPI hotplug code and docking stations.  They both are somewhat
cumbersome to use and work slightly differently.

The users of alloc_acpi_hp_work() have to submit a work function that
will extract the necessary data items from a struct acpi_hp_work
object allocated by alloc_acpi_hp_work() and then will free that
object, while it would be more straightforward to simply use a work
function with one more argument and let the interface take care of
the execution details.

The users of acpi_os_hotplug_execute() also have to deal with the
fact that it takes only one argument in addition to the work function
pointer, although acpi_os_execute_deferred() actually takes care of
the allocation and freeing of memory, so it would have been able to
pass more arguments to the work function if it hadn't been
constrained by the connection with acpi_os_execute().

Moreover, while alloc_acpi_hp_work() makes GFP_KERNEL memory
allocations, which is correct, because hotplug work items are
always queued up from process context, acpi_os_hotplug_execute()
uses GFP_ATOMIC, as that is needed by acpi_os_execute().  Also,
acpi_os_execute_deferred() queued up by it waits for the ACPI event
workqueues to flush before executing the work function, whereas
alloc_acpi_hp_work() can't do anything similar.  That leads to
somewhat arbitrary differences in behavior between various ACPI
hotplug code paths and has to be straightened up.

For this reason, replace both alloc_acpi_hp_work() and
acpi_os_hotplug_execute() with a single interface,
acpi_hotplug_execute(), combining their behavior and being more
friendly to its users than any of the two.

Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
Tested-by: Mika Westerberg &lt;mika.westerberg@linux.intel.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
There are two different interfaces for queuing up work items on the
ACPI hotplug workqueue, alloc_acpi_hp_work() used by PCI and PCI host
bridge hotplug code and acpi_os_hotplug_execute() used by the common
ACPI hotplug code and docking stations.  They both are somewhat
cumbersome to use and work slightly differently.

The users of alloc_acpi_hp_work() have to submit a work function that
will extract the necessary data items from a struct acpi_hp_work
object allocated by alloc_acpi_hp_work() and then will free that
object, while it would be more straightforward to simply use a work
function with one more argument and let the interface take care of
the execution details.

The users of acpi_os_hotplug_execute() also have to deal with the
fact that it takes only one argument in addition to the work function
pointer, although acpi_os_execute_deferred() actually takes care of
the allocation and freeing of memory, so it would have been able to
pass more arguments to the work function if it hadn't been
constrained by the connection with acpi_os_execute().

Moreover, while alloc_acpi_hp_work() makes GFP_KERNEL memory
allocations, which is correct, because hotplug work items are
always queued up from process context, acpi_os_hotplug_execute()
uses GFP_ATOMIC, as that is needed by acpi_os_execute().  Also,
acpi_os_execute_deferred() queued up by it waits for the ACPI event
workqueues to flush before executing the work function, whereas
alloc_acpi_hp_work() can't do anything similar.  That leads to
somewhat arbitrary differences in behavior between various ACPI
hotplug code paths and has to be straightened up.

For this reason, replace both alloc_acpi_hp_work() and
acpi_os_hotplug_execute() with a single interface,
acpi_hotplug_execute(), combining their behavior and being more
friendly to its users than any of the two.

Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
Tested-by: Mika Westerberg &lt;mika.westerberg@linux.intel.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ACPI / hotplug: Carry out PCI root eject directly</title>
<updated>2013-11-07T00:42:09+00:00</updated>
<author>
<name>Rafael J. Wysocki</name>
<email>rafael.j.wysocki@intel.com</email>
</author>
<published>2013-11-07T00:42:09+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=43d388832bd3e413e9b5e6f3caef4b0844b901af'/>
<id>43d388832bd3e413e9b5e6f3caef4b0844b901af</id>
<content type='text'>
Since _handle_hotplug_event_root() is run from the ACPI hotplug
workqueue, it doesn't need to queue up a work item to eject a PCI
host bridge on the same workqueue.  Instead, it can just carry out
the eject by calling acpi_bus_device_eject() directly, so make that
happen.

Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Since _handle_hotplug_event_root() is run from the ACPI hotplug
workqueue, it doesn't need to queue up a work item to eject a PCI
host bridge on the same workqueue.  Instead, it can just carry out
the eject by calling acpi_bus_device_eject() directly, so make that
happen.

Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ACPI / hotplug: Make acpi_bus_hot_remove_device() internal</title>
<updated>2013-11-07T00:41:48+00:00</updated>
<author>
<name>Rafael J. Wysocki</name>
<email>rafael.j.wysocki@intel.com</email>
</author>
<published>2013-11-07T00:41:48+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=ace8238b00eafd493b8dbcc7db813ed72b8b6e87'/>
<id>ace8238b00eafd493b8dbcc7db813ed72b8b6e87</id>
<content type='text'>
Notice that handle_root_bridge_removal() is the only user of
acpi_bus_hot_remove_device(), so it doesn't have to be exported
any more and can be made internal to the ACPI core.

Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
Acked-by: Toshi Kani &lt;toshi.kani@hp.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Notice that handle_root_bridge_removal() is the only user of
acpi_bus_hot_remove_device(), so it doesn't have to be exported
any more and can be made internal to the ACPI core.

Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
Acked-by: Toshi Kani &lt;toshi.kani@hp.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ACPI: Remove acpi_pci_slot_init() headers from internal.h</title>
<updated>2013-11-07T00:40:50+00:00</updated>
<author>
<name>Rafael J. Wysocki</name>
<email>rafael.j.wysocki@intel.com</email>
</author>
<published>2013-11-07T00:40:50+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=71bba8fafac8975dbb684df4098d2dd6baac1fda'/>
<id>71bba8fafac8975dbb684df4098d2dd6baac1fda</id>
<content type='text'>
Since acpi_pci_slot_init() is now called from acpi_pci_init()
and pci-acpi.h contains its header, remove that header (and the
empty definition of that function for CONFIG_ACPI_PCI_SLOT unset)
from internal.h as it doesn't have to be there any more.  That also
avoids a build warning about duplicate function definitions for
CONFIG_ACPI_PCI_SLOT unset.

Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Since acpi_pci_slot_init() is now called from acpi_pci_init()
and pci-acpi.h contains its header, remove that header (and the
empty definition of that function for CONFIG_ACPI_PCI_SLOT unset)
from internal.h as it doesn't have to be there any more.  That also
avoids a build warning about duplicate function definitions for
CONFIG_ACPI_PCI_SLOT unset.

Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ACPI / video: Do not register backlight if win8 and native interface exists</title>
<updated>2013-10-15T23:16:04+00:00</updated>
<author>
<name>Aaron Lu</name>
<email>aaron.lu@intel.com</email>
</author>
<published>2013-10-11T13:27:45+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=fbc9fe1b4f222a7c575e3bd8e9defe59c6190a04'/>
<id>fbc9fe1b4f222a7c575e3bd8e9defe59c6190a04</id>
<content type='text'>
According to Matthew Garrett, "Windows 8 leaves backlight control up
to individual graphics drivers rather than making ACPI calls itself.
There's plenty of evidence to suggest that the Intel driver for
Windows [8] doesn't use the ACPI interface, including the fact that
it's broken on a bunch of machines when the OS claims to support
Windows 8.  The simplest thing to do appears to be to disable the
ACPI backlight interface on these systems".

So for Win8 systems, if there is native backlight control interface
registered by GPU driver, ACPI video does not need to register its own.
Since there are systems that don't work well with this approach, a
parameter for video module named use_native_backlight is introduced and
has the value of false by default. For users who have a broken ACPI
video backlight interface, video.use_native_backlight=1 is needed in
kernel cmdline.

Signed-off-by: Aaron Lu &lt;aaron.lu@intel.com&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
According to Matthew Garrett, "Windows 8 leaves backlight control up
to individual graphics drivers rather than making ACPI calls itself.
There's plenty of evidence to suggest that the Intel driver for
Windows [8] doesn't use the ACPI interface, including the fact that
it's broken on a bunch of machines when the OS claims to support
Windows 8.  The simplest thing to do appears to be to disable the
ACPI backlight interface on these systems".

So for Win8 systems, if there is native backlight control interface
registered by GPU driver, ACPI video does not need to register its own.
Since there are systems that don't work well with this approach, a
parameter for video module named use_native_backlight is introduced and
has the value of false by default. For users who have a broken ACPI
video backlight interface, video.use_native_backlight=1 is needed in
kernel cmdline.

Signed-off-by: Aaron Lu &lt;aaron.lu@intel.com&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>Merge back earlier 'acpi-assorted' material</title>
<updated>2013-08-14T21:22:45+00:00</updated>
<author>
<name>Rafael J. Wysocki</name>
<email>rafael.j.wysocki@intel.com</email>
</author>
<published>2013-08-14T21:22:45+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=f3ce717e60572421f56d89c9a85ac42e634d16e7'/>
<id>f3ce717e60572421f56d89c9a85ac42e634d16e7</id>
<content type='text'>
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
</pre>
</div>
</content>
</entry>
<entry>
<title>Revert "ACPI / video / i915: No ACPI backlight if firmware expects Windows 8"</title>
<updated>2013-07-26T12:59:20+00:00</updated>
<author>
<name>Rafael J. Wysocki</name>
<email>rafael.j.wysocki@intel.com</email>
</author>
<published>2013-07-25T19:43:39+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=8e5c2b776ae4c35f54547c017e0a943429f5748a'/>
<id>8e5c2b776ae4c35f54547c017e0a943429f5748a</id>
<content type='text'>
We attempted to address a regression introduced by commit a57f7f9
(ACPICA: Add Windows8/Server2012 string for _OSI method.) after which
ACPI video backlight support doesn't work on a number of systems,
because the relevant AML methods in the ACPI tables in their BIOSes
become useless after the BIOS has been told that the OS is compatible
with Windows 8.  That problem is tracked by the bug entry at:

https://bugzilla.kernel.org/show_bug.cgi?id=51231

Commit 8c5bd7a (ACPI / video / i915: No ACPI backlight if firmware
expects Windows 8) introduced for this purpose essentially prevented
the ACPI backlight support from being used if the BIOS had been told
that the OS was compatible with Windows 8 and the i915 driver was
loaded, in which case the backlight would always be handled by i915.
Unfortunately, however, that turned out to cause problems with
backlight to appear on multiple systems with symptoms indicating that
i915 was unable to control the backlight on those systems as
expected.

For this reason, revert commit 8c5bd7a, but leave the function
acpi_video_backlight_quirks() introduced by it, because another
commit on top of it uses that function.

References: https://lkml.org/lkml/2013/7/21/119
References: https://lkml.org/lkml/2013/7/22/261
References: https://lkml.org/lkml/2013/7/23/429
References: https://lkml.org/lkml/2013/7/23/459
References: https://lkml.org/lkml/2013/7/23/81
References: https://lkml.org/lkml/2013/7/24/27
Reported-and-tested-by: James Hogan &lt;james@albanarts.com&gt;
Reported-and-tested-by: Kamal Mostafa &lt;kamal@canonical.com&gt;
Reported-and-tested-by: Jörg Otte &lt;jrg.otte@gmail.com&gt;
Reported-and-tested-by: Steven Newbury &lt;steve@snewbury.org.uk&gt;
Reported-by: Martin Steigerwald &lt;Martin@lichtvoll.de&gt;
Reported-by: Kalle Valo &lt;kvalo@adurom.com&gt;
Tested-by: Joerg Platte &lt;jplatte@naasa.net&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
We attempted to address a regression introduced by commit a57f7f9
(ACPICA: Add Windows8/Server2012 string for _OSI method.) after which
ACPI video backlight support doesn't work on a number of systems,
because the relevant AML methods in the ACPI tables in their BIOSes
become useless after the BIOS has been told that the OS is compatible
with Windows 8.  That problem is tracked by the bug entry at:

https://bugzilla.kernel.org/show_bug.cgi?id=51231

Commit 8c5bd7a (ACPI / video / i915: No ACPI backlight if firmware
expects Windows 8) introduced for this purpose essentially prevented
the ACPI backlight support from being used if the BIOS had been told
that the OS was compatible with Windows 8 and the i915 driver was
loaded, in which case the backlight would always be handled by i915.
Unfortunately, however, that turned out to cause problems with
backlight to appear on multiple systems with symptoms indicating that
i915 was unable to control the backlight on those systems as
expected.

For this reason, revert commit 8c5bd7a, but leave the function
acpi_video_backlight_quirks() introduced by it, because another
commit on top of it uses that function.

References: https://lkml.org/lkml/2013/7/21/119
References: https://lkml.org/lkml/2013/7/22/261
References: https://lkml.org/lkml/2013/7/23/429
References: https://lkml.org/lkml/2013/7/23/459
References: https://lkml.org/lkml/2013/7/23/81
References: https://lkml.org/lkml/2013/7/24/27
Reported-and-tested-by: James Hogan &lt;james@albanarts.com&gt;
Reported-and-tested-by: Kamal Mostafa &lt;kamal@canonical.com&gt;
Reported-and-tested-by: Jörg Otte &lt;jrg.otte@gmail.com&gt;
Reported-and-tested-by: Steven Newbury &lt;steve@snewbury.org.uk&gt;
Reported-by: Martin Steigerwald &lt;Martin@lichtvoll.de&gt;
Reported-by: Kalle Valo &lt;kvalo@adurom.com&gt;
Tested-by: Joerg Platte &lt;jplatte@naasa.net&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ACPI: Cleanup sparse warning on acpi_os_initialize1()</title>
<updated>2013-07-25T22:36:00+00:00</updated>
<author>
<name>Lv Zheng</name>
<email>lv.zheng@intel.com</email>
</author>
<published>2013-07-23T08:11:55+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=1129c92faa069581bf3acf34cae92477bd6161d8'/>
<id>1129c92faa069581bf3acf34cae92477bd6161d8</id>
<content type='text'>
This patch cleans up the following sparse warning:

# make C=2 drivers/acpi/osl.o
...
drivers/acpi/osl.c:1775:20: warning: symbol 'acpi_os_initialize1' was not declared. Should it be static?
...
  CC      drivers/acpi/osl.o

Signed-off-by: Lv Zheng &lt;lv.zheng@intel.com&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
This patch cleans up the following sparse warning:

# make C=2 drivers/acpi/osl.o
...
drivers/acpi/osl.c:1775:20: warning: symbol 'acpi_os_initialize1' was not declared. Should it be static?
...
  CC      drivers/acpi/osl.o

Signed-off-by: Lv Zheng &lt;lv.zheng@intel.com&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>ACPI / video / i915: No ACPI backlight if firmware expects Windows 8</title>
<updated>2013-07-18T00:08:06+00:00</updated>
<author>
<name>Rafael J. Wysocki</name>
<email>rafael.j.wysocki@intel.com</email>
</author>
<published>2013-07-18T00:08:06+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=8c5bd7adb2ce47e6aa39d17b2375f69b0c0aa255'/>
<id>8c5bd7adb2ce47e6aa39d17b2375f69b0c0aa255</id>
<content type='text'>
According to Matthew Garrett, "Windows 8 leaves backlight control up
to individual graphics drivers rather than making ACPI calls itself.
There's plenty of evidence to suggest that the Intel driver for
Windows [8] doesn't use the ACPI interface, including the fact that
it's broken on a bunch of machines when the OS claims to support
Windows 8.  The simplest thing to do appears to be to disable the
ACPI backlight interface on these systems".

There's a problem with that approach, however, because simply
avoiding to register the ACPI backlight interface if the firmware
calls _OSI for Windows 8 may not work in the following situations:
 (1) The ACPI backlight interface actually works on the given system
     and the i915 driver is not loaded (e.g. another graphics driver
     is used).
 (2) The ACPI backlight interface doesn't work on the given system,
     but there is a vendor platform driver that will register its
     own, equally broken, backlight interface if not prevented from
     doing so by the ACPI subsystem.
Therefore we need to allow the ACPI backlight interface to be
registered until the i915 driver is loaded which then will unregister
it if the firmware has called _OSI for Windows 8 (or will register
the ACPI video driver without backlight support if not already
present).

For this reason, introduce an alternative function for registering
ACPI video, acpi_video_register_with_quirks(), that will check
whether or not the ACPI video driver has already been registered
and whether or not the backlight Windows 8 quirk has to be applied.
If the quirk has to be applied, it will block the ACPI backlight
support and either unregister the backlight interface if the ACPI
video driver has already been registered, or register the ACPI
video driver without the backlight interface otherwise.  Make
the i915 driver use acpi_video_register_with_quirks() instead of
acpi_video_register() in i915_driver_load().

This change is based on earlier patches from Matthew Garrett,
Chun-Yi Lee and Seth Forshee and includes a fix from Aaron Lu's.

References: https://bugzilla.kernel.org/show_bug.cgi?id=51231
Tested-by: Aaron Lu &lt;aaron.lu@intel.com&gt;
Tested-by: Igor Gnatenko &lt;i.gnatenko.brain@gmail.com&gt;
Tested-by: Yves-Alexis Perez &lt;corsac@debian.org&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
Reviewed-by: Aaron Lu &lt;aaron.lu@intel.com&gt;
Acked-by: Matthew Garrett &lt;matthew.garrett@nebula.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
According to Matthew Garrett, "Windows 8 leaves backlight control up
to individual graphics drivers rather than making ACPI calls itself.
There's plenty of evidence to suggest that the Intel driver for
Windows [8] doesn't use the ACPI interface, including the fact that
it's broken on a bunch of machines when the OS claims to support
Windows 8.  The simplest thing to do appears to be to disable the
ACPI backlight interface on these systems".

There's a problem with that approach, however, because simply
avoiding to register the ACPI backlight interface if the firmware
calls _OSI for Windows 8 may not work in the following situations:
 (1) The ACPI backlight interface actually works on the given system
     and the i915 driver is not loaded (e.g. another graphics driver
     is used).
 (2) The ACPI backlight interface doesn't work on the given system,
     but there is a vendor platform driver that will register its
     own, equally broken, backlight interface if not prevented from
     doing so by the ACPI subsystem.
Therefore we need to allow the ACPI backlight interface to be
registered until the i915 driver is loaded which then will unregister
it if the firmware has called _OSI for Windows 8 (or will register
the ACPI video driver without backlight support if not already
present).

For this reason, introduce an alternative function for registering
ACPI video, acpi_video_register_with_quirks(), that will check
whether or not the ACPI video driver has already been registered
and whether or not the backlight Windows 8 quirk has to be applied.
If the quirk has to be applied, it will block the ACPI backlight
support and either unregister the backlight interface if the ACPI
video driver has already been registered, or register the ACPI
video driver without the backlight interface otherwise.  Make
the i915 driver use acpi_video_register_with_quirks() instead of
acpi_video_register() in i915_driver_load().

This change is based on earlier patches from Matthew Garrett,
Chun-Yi Lee and Seth Forshee and includes a fix from Aaron Lu's.

References: https://bugzilla.kernel.org/show_bug.cgi?id=51231
Tested-by: Aaron Lu &lt;aaron.lu@intel.com&gt;
Tested-by: Igor Gnatenko &lt;i.gnatenko.brain@gmail.com&gt;
Tested-by: Yves-Alexis Perez &lt;corsac@debian.org&gt;
Signed-off-by: Rafael J. Wysocki &lt;rafael.j.wysocki@intel.com&gt;
Reviewed-by: Aaron Lu &lt;aaron.lu@intel.com&gt;
Acked-by: Matthew Garrett &lt;matthew.garrett@nebula.com&gt;
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