Return-path: Received: from mail-yx0-f174.google.com ([209.85.213.174]:56988 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754301Ab1FTRwK (ORCPT ); Mon, 20 Jun 2011 13:52:10 -0400 Received: by mail-yx0-f174.google.com with SMTP id 11so2178645yxi.19 for ; Mon, 20 Jun 2011 10:52:10 -0700 (PDT) From: Aloisio Almeida Jr To: linville@tuxdriver.com Cc: linux-wireless@vger.kernel.org, sameo@linux.intel.com, johannes@sipsolutions.net, lauro.venancio@openbossa.org, marcio.macedo@openbossa.org, Waldemar.Rymarkiewicz@tieto.com, Aloisio Almeida Jr Subject: [RFC][PATCH v2 7/7] NFC: add Documentation/networking/nfc.txt Date: Mon, 20 Jun 2011 14:50:12 -0300 Message-Id: <1308592212-5755-8-git-send-email-aloisio.almeida@openbossa.org> (sfid-20110620_195216_070424_47AD24EE) In-Reply-To: <1308592212-5755-1-git-send-email-aloisio.almeida@openbossa.org> References: <1308592212-5755-1-git-send-email-aloisio.almeida@openbossa.org> Sender: linux-wireless-owner@vger.kernel.org List-ID: Signed-off-by: Aloisio Almeida Jr Signed-off-by: Lauro Ramos Venancio --- Documentation/networking/nfc.txt | 127 ++++++++++++++++++++++++++++++++++++++ 1 files changed, 127 insertions(+), 0 deletions(-) create mode 100644 Documentation/networking/nfc.txt diff --git a/Documentation/networking/nfc.txt b/Documentation/networking/nfc.txt new file mode 100644 index 0000000..23cf411 --- /dev/null +++ b/Documentation/networking/nfc.txt @@ -0,0 +1,127 @@ +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 exchage 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 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 was 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 an 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 specifc device + +* NFC_EVENT_DEVICE_ADDED - reports a NFC device addition +* NFC_EVENT_DEVICE_REMOVED - reports a 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. The event attributes have relevant information about the target, such as +the supported NFC protocols. The TARGETS_FOUND event has the list of all +targets found by a specific device. + +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 a +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 a 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. -- 1.7.4.1