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    Subject[PATCH v3 0/4] introduce External Connector Class (extcon)
    For external connectors, which may have different types of cables attached
    (USB, TA, HDMI, Analog A/V, and others), we often have seperated device
    drivers that detect the state changes at the port and device drivers that
    do something according to the state changes.

    For example, when MAX8997-MUIC detects a Charger cable insertion, another
    device driver (such as MAX8903 charger, MAX8997 charger, Charger Manager,
    or board file) needs to set charger current limit accordingly and when
    MAX8997-MUIC detects a HDMI cable insertion, multimedia device drivers
    need to do some operations accordingly.

    This patchset supports the usage of notifier for passing such information
    between device drivers.

    Another issue is that at a single switch port, there might be multiple
    and heterogeneous cables attached at the same time. Besides the state
    (Attached or Detached) of each cable may alter independently. Such extcon
    devices that support simultaneous mult-cable attachment include, bot not
    limited to, docks, cradles, and 30-pin-like ports (like that of NURI board
    in linux/arch/arm/mach-exynos, which resembles Samsung Galaxy Tab series).
    For example, the 30-pin port of NURI board may be used to connect analog
    audio cables, analog video cable, and a USB or a charger. Because such
    cables coonnect part of the 30 pins to external devices/cables, the
    possible combinations of external devices/cables vary significantly and
    users may fabricate their own design; e.g., an 30-pin adaptor connecting
    USB, AC-DC adaptor, HDMI, analog audio, analog video, USB-host, SD-card,
    and so on.

    In order to address such issues, Android kernel's "Switch" class seems to
    be a good basis and we have implemented "Multistate Switch Class" based on
    it. The "Switch" class code of Android kernel is GPL as well.

    Summary of changes from v2 patchset
    - Support to express mutually exclusive set of cables
    - Revised device/class/sysfs-entries add/removal methods
    - Added sysfs entries
    - Revised documentation and comments
    - Some bugfixes
    - Compatible with Android (for extcon devices with "use_class_name_switch" set)

    Summary of changes from RFC
    - ABI documentation added
    - Notifees may get notified for a state change of a specific cable, not
    every cable of the corresponding extcon.
    - Added kerneldoc comments
    - Moved to /drivers/extcon/
    - Added helper functions
    - Some bugfixes

    Donggeun Kim (1):
    Extcon: support notification based on the state changes.

    MyungJoo Ham (3):
    Extcon (external connector): import Android's switch class and
    Extcon: support multiple states at a device.
    Extcon: support mutually exclusive relation between cables.

    Documentation/ABI/testing/sysfs-class-extcon | 75 +++
    drivers/Kconfig | 2 +
    drivers/Makefile | 1 +
    drivers/extcon/Kconfig | 22 +
    drivers/extcon/Makefile | 6 +
    drivers/extcon/extcon_class.c | 641 ++++++++++++++++++++++++++
    drivers/extcon/extcon_gpio.c | 173 +++++++
    include/linux/extcon.h | 305 ++++++++++++
    8 files changed, 1225 insertions(+), 0 deletions(-)
    create mode 100644 Documentation/ABI/testing/sysfs-class-extcon
    create mode 100644 drivers/extcon/Kconfig
    create mode 100644 drivers/extcon/Makefile
    create mode 100644 drivers/extcon/extcon_class.c
    create mode 100644 drivers/extcon/extcon_gpio.c
    create mode 100644 include/linux/extcon.h


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