docs: nfc: add it to the driver-api book

Most of the descriptions here are oriented to a Kernel developer.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

3 files changed, 0 insertions, 356 deletions

diff --git a/Documentation/nfc/index.rst b/Documentation/nfc/index.rst
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-:orphan:
-
-========================
-Near Field Communication
-========================
-
-.. toctree::
-   :maxdepth: 1
-
-   nfc-hci
-   nfc-pn544
diff --git a/Documentation/nfc/nfc-hci.rst b/Documentation/nfc/nfc-hci.rst
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index eb8a1a14e919..000000000000
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-========================
-HCI backend for NFC Core
-========================
-
-- Author: Eric Lapuyade, Samuel Ortiz
-- Contact: eric.lapuyade@intel.com, samuel.ortiz@intel.com
-
-General
--------
-
-The HCI layer implements much of the ETSI TS 102 622 V10.2.0 specification. It
-enables easy writing of HCI-based NFC drivers. The HCI layer runs as an NFC Core
-backend, implementing an abstract nfc device and translating NFC Core API
-to HCI commands and events.
-
-HCI
----
-
-HCI registers as an nfc device with NFC Core. Requests coming from userspace are
-routed through netlink sockets to NFC Core and then to HCI. From this point,
-they are translated in a sequence of HCI commands sent to the HCI layer in the
-host controller (the chip). Commands can be executed synchronously (the sending
-context blocks waiting for response) or asynchronously (the response is returned
-from HCI Rx context).
-HCI events can also be received from the host controller. They will be handled
-and a translation will be forwarded to NFC Core as needed. There are hooks to
-let the HCI driver handle proprietary events or override standard behavior.
-HCI uses 2 execution contexts:
-
-- one for executing commands : nfc_hci_msg_tx_work(). Only one command
-  can be executing at any given moment.
-- one for dispatching received events and commands : nfc_hci_msg_rx_work().
-
-HCI Session initialization
---------------------------
-
-The Session initialization is an HCI standard which must unfortunately
-support proprietary gates. This is the reason why the driver will pass a list
-of proprietary gates that must be part of the session. HCI will ensure all
-those gates have pipes connected when the hci device is set up.
-In case the chip supports pre-opened gates and pseudo-static pipes, the driver
-can pass that information to HCI core.
-
-HCI Gates and Pipes
--------------------
-
-A gate defines the 'port' where some service can be found. In order to access
-a service, one must create a pipe to that gate and open it. In this
-implementation, pipes are totally hidden. The public API only knows gates.
-This is consistent with the driver need to send commands to proprietary gates
-without knowing the pipe connected to it.
-
-Driver interface
-----------------
-
-A driver is generally written in two parts : the physical link management and
-the HCI management. This makes it easier to maintain a driver for a chip that
-can be connected using various phy (i2c, spi, ...)
-
-HCI Management
---------------
-
-A driver would normally register itself with HCI and provide the following
-entry points::
-
-  struct nfc_hci_ops {
-	int (*open)(struct nfc_hci_dev *hdev);
-	void (*close)(struct nfc_hci_dev *hdev);
-	int (*hci_ready) (struct nfc_hci_dev *hdev);
-	int (*xmit) (struct nfc_hci_dev *hdev, struct sk_buff *skb);
-	int (*start_poll) (struct nfc_hci_dev *hdev,
-			   u32 im_protocols, u32 tm_protocols);
-	int (*dep_link_up)(struct nfc_hci_dev *hdev, struct nfc_target *target,
-			   u8 comm_mode, u8 *gb, size_t gb_len);
-	int (*dep_link_down)(struct nfc_hci_dev *hdev);
-	int (*target_from_gate) (struct nfc_hci_dev *hdev, u8 gate,
-				 struct nfc_target *target);
-	int (*complete_target_discovered) (struct nfc_hci_dev *hdev, u8 gate,
-					   struct nfc_target *target);
-	int (*im_transceive) (struct nfc_hci_dev *hdev,
-			      struct nfc_target *target, struct sk_buff *skb,
-			      data_exchange_cb_t cb, void *cb_context);
-	int (*tm_send)(struct nfc_hci_dev *hdev, struct sk_buff *skb);
-	int (*check_presence)(struct nfc_hci_dev *hdev,
-			      struct nfc_target *target);
-	int (*event_received)(struct nfc_hci_dev *hdev, u8 gate, u8 event,
-			      struct sk_buff *skb);
-  };
-
-- open() and close() shall turn the hardware on and off.
-- hci_ready() is an optional entry point that is called right after the hci
-  session has been set up. The driver can use it to do additional initialization
-  that must be performed using HCI commands.
-- xmit() shall simply write a frame to the physical link.
-- start_poll() is an optional entrypoint that shall set the hardware in polling
-  mode. This must be implemented only if the hardware uses proprietary gates or a
-  mechanism slightly different from the HCI standard.
-- dep_link_up() is called after a p2p target has been detected, to finish
-  the p2p connection setup with hardware parameters that need to be passed back
-  to nfc core.
-- dep_link_down() is called to bring the p2p link down.
-- target_from_gate() is an optional entrypoint to return the nfc protocols
-  corresponding to a proprietary gate.
-- complete_target_discovered() is an optional entry point to let the driver
-  perform additional proprietary processing necessary to auto activate the
-  discovered target.
-- im_transceive() must be implemented by the driver if proprietary HCI commands
-  are required to send data to the tag. Some tag types will require custom
-  commands, others can be written to using the standard HCI commands. The driver
-  can check the tag type and either do proprietary processing, or return 1 to ask
-  for standard processing. The data exchange command itself must be sent
-  asynchronously.
-- tm_send() is called to send data in the case of a p2p connection
-- check_presence() is an optional entry point that will be called regularly
-  by the core to check that an activated tag is still in the field. If this is
-  not implemented, the core will not be able to push tag_lost events to the user
-  space
-- event_received() is called to handle an event coming from the chip. Driver
-  can handle the event or return 1 to let HCI attempt standard processing.
-
-On the rx path, the driver is responsible to push incoming HCP frames to HCI
-using nfc_hci_recv_frame(). HCI will take care of re-aggregation and handling
-This must be done from a context that can sleep.
-
-PHY Management
---------------
-
-The physical link (i2c, ...) management is defined by the following structure::
-
-  struct nfc_phy_ops {
-	int (*write)(void *dev_id, struct sk_buff *skb);
-	int (*enable)(void *dev_id);
-	void (*disable)(void *dev_id);
-  };
-
-enable():
-	turn the phy on (power on), make it ready to transfer data
-disable():
-	turn the phy off
-write():
-	Send a data frame to the chip. Note that to enable higher
-	layers such as an llc to store the frame for re-emission, this
-	function must not alter the skb. It must also not return a positive
-	result (return 0 for success, negative for failure).
-
-Data coming from the chip shall be sent directly to nfc_hci_recv_frame().
-
-LLC
----
-
-Communication between the CPU and the chip often requires some link layer
-protocol. Those are isolated as modules managed by the HCI layer. There are
-currently two modules : nop (raw transfert) and shdlc.
-A new llc must implement the following functions::
-
-  struct nfc_llc_ops {
-	void *(*init) (struct nfc_hci_dev *hdev, xmit_to_drv_t xmit_to_drv,
-		       rcv_to_hci_t rcv_to_hci, int tx_headroom,
-		       int tx_tailroom, int *rx_headroom, int *rx_tailroom,
-		       llc_failure_t llc_failure);
-	void (*deinit) (struct nfc_llc *llc);
-	int (*start) (struct nfc_llc *llc);
-	int (*stop) (struct nfc_llc *llc);
-	void (*rcv_from_drv) (struct nfc_llc *llc, struct sk_buff *skb);
-	int (*xmit_from_hci) (struct nfc_llc *llc, struct sk_buff *skb);
-  };
-
-init():
-	allocate and init your private storage
-deinit():
-	cleanup
-start():
-	establish the logical connection
-stop ():
-	terminate the logical connection
-rcv_from_drv():
-	handle data coming from the chip, going to HCI
-xmit_from_hci():
-	handle data sent by HCI, going to the chip
-
-The llc must be registered with nfc before it can be used. Do that by
-calling::
-
-	nfc_llc_register(const char *name, struct nfc_llc_ops *ops);
-
-Again, note that the llc does not handle the physical link. It is thus very
-easy to mix any physical link with any llc for a given chip driver.
-
-Included Drivers
-----------------
-
-An HCI based driver for an NXP PN544, connected through I2C bus, and using
-shdlc is included.
-
-Execution Contexts
-------------------
-
-The execution contexts are the following:
-- IRQ handler (IRQH):
-fast, cannot sleep. sends incoming frames to HCI where they are passed to
-the current llc. In case of shdlc, the frame is queued in shdlc rx queue.
-
-- SHDLC State Machine worker (SMW)
-
-  Only when llc_shdlc is used: handles shdlc rx & tx queues.
-
-  Dispatches HCI cmd responses.
-
-- HCI Tx Cmd worker (MSGTXWQ)
-
-  Serializes execution of HCI commands.
-
-  Completes execution in case of response timeout.
-
-- HCI Rx worker (MSGRXWQ)
-
-  Dispatches incoming HCI commands or events.
-
-- Syscall context from a userspace call (SYSCALL)
-
-  Any entrypoint in HCI called from NFC Core
-
-Workflow executing an HCI command (using shdlc)
------------------------------------------------
-
-Executing an HCI command can easily be performed synchronously using the
-following API::
-
-  int nfc_hci_send_cmd (struct nfc_hci_dev *hdev, u8 gate, u8 cmd,
-			const u8 *param, size_t param_len, struct sk_buff **skb)
-
-The API must be invoked from a context that can sleep. Most of the time, this
-will be the syscall context. skb will return the result that was received in
-the response.
-
-Internally, execution is asynchronous. So all this API does is to enqueue the
-HCI command, setup a local wait queue on stack, and wait_event() for completion.
-The wait is not interruptible because it is guaranteed that the command will
-complete after some short timeout anyway.
-
-MSGTXWQ context will then be scheduled and invoke nfc_hci_msg_tx_work().
-This function will dequeue the next pending command and send its HCP fragments
-to the lower layer which happens to be shdlc. It will then start a timer to be
-able to complete the command with a timeout error if no response arrive.
-
-SMW context gets scheduled and invokes nfc_shdlc_sm_work(). This function
-handles shdlc framing in and out. It uses the driver xmit to send frames and
-receives incoming frames in an skb queue filled from the driver IRQ handler.
-SHDLC I(nformation) frames payload are HCP fragments. They are aggregated to
-form complete HCI frames, which can be a response, command, or event.
-
-HCI Responses are dispatched immediately from this context to unblock
-waiting command execution. Response processing involves invoking the completion
-callback that was provided by nfc_hci_msg_tx_work() when it sent the command.
-The completion callback will then wake the syscall context.
-
-It is also possible to execute the command asynchronously using this API::
-
-  static int nfc_hci_execute_cmd_async(struct nfc_hci_dev *hdev, u8 pipe, u8 cmd,
-				       const u8 *param, size_t param_len,
-				       data_exchange_cb_t cb, void *cb_context)
-
-The workflow is the same, except that the API call returns immediately, and
-the callback will be called with the result from the SMW context.
-
-Workflow receiving an HCI event or command
-------------------------------------------
-
-HCI commands or events are not dispatched from SMW context. Instead, they are
-queued to HCI rx_queue and will be dispatched from HCI rx worker
-context (MSGRXWQ). This is done this way to allow a cmd or event handler
-to also execute other commands (for example, handling the
-NFC_HCI_EVT_TARGET_DISCOVERED event from PN544 requires to issue an
-ANY_GET_PARAMETER to the reader A gate to get information on the target
-that was discovered).
-
-Typically, such an event will be propagated to NFC Core from MSGRXWQ context.
-
-Error management
-----------------
-
-Errors that occur synchronously with the execution of an NFC Core request are
-simply returned as the execution result of the request. These are easy.
-
-Errors that occur asynchronously (e.g. in a background protocol handling thread)
-must be reported such that upper layers don't stay ignorant that something
-went wrong below and know that expected events will probably never happen.
-Handling of these errors is done as follows:
-
-- driver (pn544) fails to deliver an incoming frame: it stores the error such
-  that any subsequent call to the driver will result in this error. Then it
-  calls the standard nfc_shdlc_recv_frame() with a NULL argument to report the
-  problem above. shdlc stores a EREMOTEIO sticky status, which will trigger
-  SMW to report above in turn.
-
-- SMW is basically a background thread to handle incoming and outgoing shdlc
-  frames. This thread will also check the shdlc sticky status and report to HCI
-  when it discovers it is not able to run anymore because of an unrecoverable
-  error that happened within shdlc or below. If the problem occurs during shdlc
-  connection, the error is reported through the connect completion.
-
-- HCI: if an internal HCI error happens (frame is lost), or HCI is reported an
-  error from a lower layer, HCI will either complete the currently executing
-  command with that error, or notify NFC Core directly if no command is
-  executing.
-
-- NFC Core: when NFC Core is notified of an error from below and polling is
-  active, it will send a tag discovered event with an empty tag list to the user
-  space to let it know that the poll operation will never be able to detect a
-  tag. If polling is not active and the error was sticky, lower levels will
-  return it at next invocation.
diff --git a/Documentation/nfc/nfc-pn544.rst b/Documentation/nfc/nfc-pn544.rst
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-============================================================================
-Kernel driver for the NXP Semiconductors PN544 Near Field Communication chip
-============================================================================
-
-
-General
--------
-
-The PN544 is an integrated transmission module for contactless
-communication. The driver goes under drives/nfc/ and is compiled as a
-module named "pn544".
-
-Host Interfaces: I2C, SPI and HSU, this driver supports currently only I2C.
-
-Protocols
----------
-
-In the normal (HCI) mode and in the firmware update mode read and
-write functions behave a bit differently because the message formats
-or the protocols are different.
-
-In the normal (HCI) mode the protocol used is derived from the ETSI
-HCI specification. The firmware is updated using a specific protocol,
-which is different from HCI.
-
-HCI messages consist of an eight bit header and the message body. The
-header contains the message length. Maximum size for an HCI message is
-33. In HCI mode sent messages are tested for a correct
-checksum. Firmware update messages have the length in the second (MSB)
-and third (LSB) bytes of the message. The maximum FW message length is
-1024 bytes.
-
-For the ETSI HCI specification see
-http://www.etsi.org/WebSite/Technologies/ProtocolSpecification.aspx