backlight: introduce backlight_device_registered

Introduce a new API for modules to query if a specific type of backlight
device has been registered. This is useful for some backlight device
provider module (e.g. ACPI video) to know if a native control
interface(e.g. the interface created by i915) is available and then do
things accordingly (e.g. avoid registering its own on Win8 systems).

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / video: seperate backlight control and event interface

The backlight control and event delivery functionality provided by ACPI
video module is mixed together and registered all during video device
enumeration time. As a result, the two functionality are also removed
together on module unload time or by the acpi_video_unregister function.
The two functionalities are actually independent and one may be useful
while the other one may be broken, so it is desirable to seperate the
two functionalities such that it is clear and easy to disable one
functionality without affecting the other one.

APIs to selectively remove backlight control interface and/or event
delivery functionality can be easily added once needed.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / video: Do not register backlight if win8 and native interface exists

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 <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
thinkpad-acpi: fix handle locate for video and query of _BCL

The tpacpi_acpi_handle_locate function makes use of acpi_get_devices to
locate handle for ACPI video by HID, the problem is, ACPI video node
doesn't really have HID defined(i.e. no _HID control method is defined
for video device), so.. that function would fail. This can be solved by
enhancing the callback function for acpi_get_devices, where we can use
acpi_device_hid function to check if the ACPI node corresponds to a
video controller.

In addition to that, the _BCL control method only exists under a video
output device node, not a video controller device node. So to evaluate
_BCL, we need the handle of a video output device node, which is child
of the located video controller node from tpacpi_acpi_handle_locate.

The two fix are necessary for some Thinkpad models to emit notification
on backlight hotkey press as a result of evaluation of _BCL.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Tested-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Merge branch 'acpi-video-next' into bleeding-edge

* acpi-video-next:
  thinkpad-acpi: fix handle locate for video and query of _BCL
  ACPI / video: Do not register backlight if win8 and native interface exists
  ACPI / video: seperate backlight control and event interface
  backlight: introduce backlight_device_registered
ACPI / AC: Remove AC's proc directory.

AC's proc directory is not used and so remove it. Prepare for removing
/proc/acpi directory.

Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Merge branch 'acpi-conversion-next' into bleeding-edge

* acpi-conversion-next:
  ACPI / AC: Remove AC's proc directory.
ACPI / video: Add Lenovo IdeaPad Yoga 13 to acpi video detect blacklist

On the Yoga 13 the backlight control doesn't work via ACPI. (And doesn't
work either with the low-level platform driver ideapad_laptop; but
works correctly via the intel video driver).  This patch hence adds the
Yoga 13 to the ACPI video detect blacklist, to make sure the broken ACPI
backlight device is never exposed to userspace.

Note that this appears unrelated to the Windows 8 backlight issues tracked
here:

https://bugzilla.kernel.org/show_bug.cgi?id=51231
https://bugzilla.kernel.org/show_bug.cgi?id=60682

The Yoga's ACPI backlight controls work neither with nor without
acpi_osi="!Windows 2012" on the kernel command line. It appears that
backlight control via the EC simply is not available at all, regardless
whether done via ACPI or via the vendor driver.

Signed-off-by: Lennart Poettering <lennart@poettering.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Merge branch 'acpi-video-next' into bleeding-edge

* acpi-video-next:
  ACPI / video: Add Lenovo IdeaPad Yoga 13 to acpi video detect blacklist