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NFC: update HCI documentation

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Signed-off-by: Eric Lapuyade <eric.lapuyade@intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
This commit is contained in:
Eric Lapuyade 2012-12-18 17:35:02 +01:00 committed by Samuel Ortiz
parent a0f36536ac
commit 2ad554a502
1 changed files with 103 additions and 26 deletions
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129
Documentation/nfc/nfc-hci.txt
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@ -17,10 +17,12 @@ 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.
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.
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.
@ -33,6 +35,8 @@ 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
-------------------
@ -46,6 +50,13 @@ 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:
@ -53,58 +64,113 @@ 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 (*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 (*data_exchange) (struct nfc_hci_dev *hdev,
struct nfc_target *target,
struct sk_buff *skb, struct sk_buff **res_skb);
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 chip.
- 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.
- data_exchange() must be implemented by the driver if proprietary HCI commands
- 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.
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.
SHDLC
-----
PHY Management
--------------
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.
The physical link (i2c, ...) management is defined by the following struture:
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
----------------
@ -117,10 +183,12 @@ Execution Contexts
The execution contexts are the following:
- IRQ handler (IRQH):
fast, cannot sleep. stores incoming frames into an shdlc rx queue
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)
handles shdlc rx & tx queues. Dispatches HCI cmd responses.
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
@ -166,6 +234,15 @@ 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
------------------------------------------