net-caif: add CAIF documentation
Documentation of the CAIF Protocol.
Signed-off-by: Sjur Braendeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/networking/caif/README b/Documentation/networking/caif/README
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+Copyright (C) ST-Ericsson AB 2010
+Author: Sjur Brendeland/ sjur.brandeland@stericsson.com
+License terms: GNU General Public License (GPL) version 2
+---------------------------------------------------------
+
+=== Start ===
+If you have compiled CAIF for modules do:
+
+$modprobe crc_ccitt
+$modprobe caif
+$modprobe caif_socket
+$modprobe chnl_net
+
+
+=== Preparing the setup with a STE modem ===
+
+If you are working on integration of CAIF you should make sure
+that the kernel is built with module support.
+
+There are some things that need to be tweaked to get the host TTY correctly
+set up to talk to the modem.
+Since the CAIF stack is running in the kernel and we want to use the existing
+TTY, we are installing our physical serial driver as a line discipline above
+the TTY device.
+
+To achieve this we need to install the N_CAIF ldisc from user space.
+The benefit is that we can hook up to any TTY.
+
+The use of Start-of-frame-extension (STX) must also be set as
+module parameter "ser_use_stx".
+
+Normally Frame Checksum is always used on UART, but this is also provided as a
+module parameter "ser_use_fcs".
+
+$ modprobe caif_serial ser_ttyname=/dev/ttyS0 ser_use_stx=yes
+$ ifconfig caif_ttyS0 up
+
+PLEASE NOTE: There is a limitation in Android shell.
+ It only accepts one argument to insmod/modprobe!
+
+=== Trouble shooting ===
+
+There are debugfs parameters provided for serial communication.
+/sys/kernel/debug/caif_serial/<tty-name>/
+
+* ser_state: Prints the bit-mask status where
+ - 0x02 means SENDING, this is a transient state.
+ - 0x10 means FLOW_OFF_SENT, i.e. the previous frame has not been sent
+ and is blocking further send operation. Flow OFF has been propagated
+ to all CAIF Channels using this TTY.
+
+* tty_status: Prints the bit-mask tty status information
+ - 0x01 - tty->warned is on.
+ - 0x02 - tty->low_latency is on.
+ - 0x04 - tty->packed is on.
+ - 0x08 - tty->flow_stopped is on.
+ - 0x10 - tty->hw_stopped is on.
+ - 0x20 - tty->stopped is on.
+
+* last_tx_msg: Binary blob Prints the last transmitted frame.
+ This can be printed with
+ $od --format=x1 /sys/kernel/debug/caif_serial/<tty>/last_rx_msg.
+ The first two tx messages sent look like this. Note: The initial
+ byte 02 is start of frame extension (STX) used for re-syncing
+ upon errors.
+
+ - Enumeration:
+ 0000000 02 05 00 00 03 01 d2 02
+ | | | | | |
+ STX(1) | | | |
+ Length(2)| | |
+ Control Channel(1)
+ Command:Enumeration(1)
+ Link-ID(1)
+ Checksum(2)
+ - Channel Setup:
+ 0000000 02 07 00 00 00 21 a1 00 48 df
+ | | | | | | | |
+ STX(1) | | | | | |
+ Length(2)| | | | |
+ Control Channel(1)
+ Command:Channel Setup(1)
+ Channel Type(1)
+ Priority and Link-ID(1)
+ Endpoint(1)
+ Checksum(2)
+
+* last_rx_msg: Prints the last transmitted frame.
+ The RX messages for LinkSetup look almost identical but they have the
+ bit 0x20 set in the command bit, and Channel Setup has added one byte
+ before Checksum containing Channel ID.
+ NOTE: Several CAIF Messages might be concatenated. The maximum debug
+ buffer size is 128 bytes.
+
+== Error Scenarios:
+- last_tx_msg contains channel setup message and last_rx_msg is empty ->
+ The host seems to be able to send over the UART, at least the CAIF ldisc get
+ notified that sending is completed.
+
+- last_tx_msg contains enumeration message and last_rx_msg is empty ->
+ The host is not able to send the message from UART, the tty has not been
+ able to complete the transmit operation.
+
+- if /sys/kernel/debug/caif_serial/<tty>/tty_status is non-zero there
+ might be problems transmitting over UART.
+ E.g. host and modem wiring is not correct you will typically see
+ tty_status = 0x10 (hw_stopped) and ser_state = 0x10 (FLOW_OFF_SENT).
+ You will probably see the enumeration message in last_tx_message
+ and empty last_rx_message.