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                Video Output Switcher Control
                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                2006 luming.yu@intel.com

The output sysfs class driver provides an abstract video output layer that
can be used to hook platform specific methods to enable/disable video output
device through common sysfs interface. For example, on my IBM ThinkPad T42
laptop, The ACPI video driver registered its output devices and read/write
method for 'state' with output sysfs class. The user interface under sysfs is:

linux:/sys/class/video_output # tree .
.
|-- CRT0
|   |-- device -> ../../../devices/pci0000:00/0000:00:01.0
|   |-- state
|   |-- subsystem -> ../../../class/video_output
|   `-- uevent
|-- DVI0
|   |-- device -> ../../../devices/pci0000:00/0000:00:01.0
|   |-- state
|   |-- subsystem -> ../../../class/video_output
|   `-- uevent
|-- LCD0
|   |-- device -> ../../../devices/pci0000:00/0000:00:01.0
|   |-- state
|   |-- subsystem -> ../../../class/video_output
|   `-- uevent
`-- TV0
   |-- device -> ../../../devices/pci0000:00/0000:00:01.0
   |-- state
   |-- subsystem -> ../../../class/video_output
   `-- uevent