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-Linux NFC subsystem
-===================
-
-The Near Field Communication (NFC) subsystem is required to standardize the
-NFC device drivers development and to create an unified userspace interface.
-
-This document covers the architecture overview, the device driver interface
-description and the userspace interface description.
-
-Architecture overview
----------------------
-
-The NFC subsystem is responsible for:
- - NFC adapters management;
- - Polling for targets;
- - Low-level data exchange;
-
-The subsystem is divided in some parts. The 'core' is responsible for
-providing the device driver interface. On the other side, it is also
-responsible for providing an interface to control operations and low-level
-data exchange.
-
-The control operations are available to userspace via generic netlink.
-
-The low-level data exchange interface is provided by the new socket family
-PF_NFC. The NFC_SOCKPROTO_RAW performs raw communication with NFC targets.
-
-
- +--------------------------------------+
- | USER SPACE |
- +--------------------------------------+
- ^ ^
- | low-level | control
- | data exchange | operations
- | |
- | v
- | +-----------+
- | AF_NFC | netlink |
- | socket +-----------+
- | raw ^
- | |
- v v
- +---------+ +-----------+
- | rawsock | <--------> | core |
- +---------+ +-----------+
- ^
- |
- v
- +-----------+
- | driver |
- +-----------+
-
-Device Driver Interface
------------------------
-
-When registering on the NFC subsystem, the device driver must inform the core
-of the set of supported NFC protocols and the set of ops callbacks. The ops
-callbacks that must be implemented are the following:
-
-* start_poll - setup the device to poll for targets
-* stop_poll - stop on progress polling operation
-* activate_target - select and initialize one of the targets found
-* deactivate_target - deselect and deinitialize the selected target
-* data_exchange - send data and receive the response (transceive operation)
-
-Userspace interface
---------------------
-
-The userspace interface is divided in control operations and low-level data
-exchange operation.
-
-CONTROL OPERATIONS:
-
-Generic netlink is used to implement the interface to the control operations.
-The operations are composed by commands and events, all listed below:
-
-* NFC_CMD_GET_DEVICE - get specific device info or dump the device list
-* NFC_CMD_START_POLL - setup a specific device to polling for targets
-* NFC_CMD_STOP_POLL - stop the polling operation in a specific device
-* NFC_CMD_GET_TARGET - dump the list of targets found by a specific device
-
-* NFC_EVENT_DEVICE_ADDED - reports an NFC device addition
-* NFC_EVENT_DEVICE_REMOVED - reports an NFC device removal
-* NFC_EVENT_TARGETS_FOUND - reports START_POLL results when 1 or more targets
-are found
-
-The user must call START_POLL to poll for NFC targets, passing the desired NFC
-protocols through NFC_ATTR_PROTOCOLS attribute. The device remains in polling
-state until it finds any target. However, the user can stop the polling
-operation by calling STOP_POLL command. In this case, it will be checked if
-the requester of STOP_POLL is the same of START_POLL.
-
-If the polling operation finds one or more targets, the event TARGETS_FOUND is
-sent (including the device id). The user must call GET_TARGET to get the list of
-all targets found by such device. Each reply message has target attributes with
-relevant information such as the supported NFC protocols.
-
-All polling operations requested through one netlink socket are stopped when
-it's closed.
-
-LOW-LEVEL DATA EXCHANGE:
-
-The userspace must use PF_NFC sockets to perform any data communication with
-targets. All NFC sockets use AF_NFC:
-
-struct sockaddr_nfc {
- sa_family_t sa_family;
- __u32 dev_idx;
- __u32 target_idx;
- __u32 nfc_protocol;
-};
-
-To establish a connection with one target, the user must create an
-NFC_SOCKPROTO_RAW socket and call the 'connect' syscall with the sockaddr_nfc
-struct correctly filled. All information comes from NFC_EVENT_TARGETS_FOUND
-netlink event. As a target can support more than one NFC protocol, the user
-must inform which protocol it wants to use.
-
-Internally, 'connect' will result in an activate_target call to the driver.
-When the socket is closed, the target is deactivated.
-
-The data format exchanged through the sockets is NFC protocol dependent. For
-instance, when communicating with MIFARE tags, the data exchanged are MIFARE
-commands and their responses.
-
-The first received package is the response to the first sent package and so
-on. In order to allow valid "empty" responses, every data received has a NULL
-header of 1 byte.