NFC: Update Documentation/nfc-hci.txt

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.

HCI uses 2 execution contexts:

- one if for executing commands : nfc_hci_msg_tx_work(). Only one command

- one for executing commands : nfc_hci_msg_tx_work(). Only one command

can be executing at any given moment.

- one if for dispatching received events and responses : nfc_hci_msg_rx_work()

- one for dispatching received events and commands : nfc_hci_msg_rx_work().

HCI Session initialization:

---------------------------

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 protocols);

	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 (*data_exchange) (struct nfc_hci_dev *hdev,

			      struct nfc_target *target,

			      struct sk_buff *skb, struct sk_buff **res_skb);

	int (*check_presence)(struct nfc_hci_dev *hdev,

			      struct nfc_target *target);

};

open() and close() shall turn the hardware on and off. xmit() shall simply

write a frame to the chip. 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.

target_from_gate() is another optional entrypoint to return the protocols

- 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 chip.

- 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.

- 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.

- data_exchange() 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.

- 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

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

handles shdlc rx & tx queues. Dispatches HCI cmd responses.

- HCI Tx Cmd worker (MSGTXWQ)

Serialize execution of HCI commands. Complete execution in case of resp timeout.

Serializes execution of HCI commands. Completes execution in case of response

timeout.

- HCI Rx worker (MSGRXWQ)

Dispatches incoming HCI commands or events.

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 agregated to

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. Reponse processing involves invoking the completion

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.