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Diffstat (limited to 'Documentation/nfc/nfc-hci.txt')
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diff --git a/Documentation/nfc/nfc-hci.txt b/Documentation/nfc/nfc-hci.txt deleted file mode 100644 index 320f933..0000000 --- a/Documentation/nfc/nfc-hci.txt +++ /dev/null @@ -1,180 +0,0 @@ -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). The sending context blocks while waiting for the -response to arrive. -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 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. - -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 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 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. -- 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 -This must be done from a context that can sleep. - -SHDLC ------ - -Most chips use shdlc to ensure integrity and delivery ordering of the HCP -frames between the host controller (the chip) and hosts (entities connected -to the chip, like the cpu). In order to simplify writing the driver, an shdlc -layer is available for use by the driver. -When used, the driver actually registers with shdlc, and shdlc will register -with HCI. HCI sees shdlc as the driver and thus send its HCP frames -through shdlc->xmit. -SHDLC adds a new execution context (nfc_shdlc_sm_work()) to run its state -machine and handle both its rx and tx path. - -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. stores incoming frames into an shdlc rx queue - -- SHDLC State Machine worker (SMW) -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. - -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. |