v5: 1 Introduce video.use_native_backlight module parameter and set its value to false by default as suggested by Rafael. For Win8 systems which have broken ACPI video backlight control, the parameter can be set to 1 in kernel cmdline to skip registering ACPI video's backlight interface. Due to this change, the acpi_video_verify_backlight_support is moved from video_detect.c to video.c - patch 3/4; 2 Rename bd_list_head and bd_list_mutex in backlight.c to backlight_dev_list and backlight_dev_list_mutex as suggested by Rafael - patch 1/4.
v4: Remove decleration and stub for acpi_video_unregister_backlight in video.h of patch 2/4 since that function doesn't exist anymore in v3.
v3: 1 Add a new patch 4/4 to fix some problems in thinkpad-acpi module; 2 Remove unnecessary function acpi_video_unregister_backlight introduced in patch 2/4 as pointed out by Jani Nikula.
v2: v1 has the subject of "Rework ACPI video driver" and is posted here: http://lkml.org/lkml/2013/9/9/74 Since the objective is really to fix Win8 backlight issues, I changed the subject in this version, sorry about that.
This patchset has four patches, the first introduced a new API named backlight_device_registered in backlight layer that can be used for backlight interface provider module to check if a specific type backlight interface has been registered, see changelog for patch 1/4 for details. Then patch 2/4 does the cleanup to sepeate the backlight control and event delivery functionality in the ACPI video module and patch 3/4 solves some Win8 backlight control problems by avoiding register ACPI video's backlight interface if: 1 Kernel cmdline option acpi_backlight=video is not given; 2 This is a Win8 system; 3 Native backlight control interface exists. Patch 4/4 fixes some problems in thinkpad-acpi module.
Technically, patch 2/4 is not required to fix the issue here. So if you think it is not necessary, I can remove it from the series.
Aaron Lu (4): backlight: introduce backlight_device_registered ACPI / video: seperate backlight control and event interface ACPI / video: Do not register backlight if win8 and native interface exists thinkpad-acpi: fix handle locate for video and query of _BCL
drivers/acpi/internal.h | 4 +- drivers/acpi/video.c | 457 ++++++++++++++++++++--------------- drivers/acpi/video_detect.c | 4 +- drivers/platform/x86/thinkpad_acpi.c | 31 ++- drivers/video/backlight/backlight.c | 31 +++ include/linux/backlight.h | 4 + 6 files changed, 326 insertions(+), 205 deletions(-)