can: ucan: add driver for Theobroma Systems UCAN devices

The UCAN driver supports the microcontroller-based USB/CAN
adapters from Theobroma Systems. There are two form-factors
that run essentially the same firmware:

* Seal: standalone USB stick ( https://www.theobroma-systems.com/seal )

* Mule: integrated on the PCB of various System-on-Modules from
  Theobroma Systems like the A31-µQ7 and the RK3399-Q7
  ( https://www.theobroma-systems.com/rk3399-q7 )

The USB wire protocol has been designed to be as generic and
hardware-indendent as possible in the hope of being useful for
implementation on other microcontrollers.

Signed-off-by: Martin Elshuber <martin.elshuber@theobroma-systems.com>
Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

2 files changed, 333 insertions, 0 deletions

diff --git a/Documentation/networking/can_ucan_protocol.rst b/Documentation/networking/can_ucan_protocol.rst
new file mode 100644
index 000000000000..4cef88d24fc7
--- /dev/null
+++ b/Documentation/networking/can_ucan_protocol.rst
@@ -0,0 +1,332 @@
+=================
+The UCAN Protocol
+=================
+
+UCAN is the protocol used by the microcontroller-based USB-CAN
+adapter that is integrated on System-on-Modules from Theobroma Systems
+and that is also available as a standalone USB stick.
+
+The UCAN protocol has been designed to be hardware-independent.
+It is modeled closely after how Linux represents CAN devices
+internally. All multi-byte integers are encoded as Little Endian.
+
+All structures mentioned in this document are defined in
+``drivers/net/can/usb/ucan.c``.
+
+USB Endpoints
+=============
+
+UCAN devices use three USB endpoints:
+
+CONTROL endpoint
+  The driver sends device management commands on this endpoint
+
+IN endpoint
+  The device sends CAN data frames and CAN error frames
+
+OUT endpoint
+  The driver sends CAN data frames on the out endpoint
+
+
+CONTROL Messages
+================
+
+UCAN devices are configured using vendor requests on the control pipe.
+
+To support multiple CAN interfaces in a single USB device all
+configuration commands target the corresponding interface in the USB
+descriptor.
+
+The driver uses ``ucan_ctrl_command_in/out`` and
+``ucan_device_request_in`` to deliver commands to the device.
+
+Setup Packet
+------------
+
+=================  =====================================================
+``bmRequestType``  Direction | Vendor | (Interface or Device)
+``bRequest``       Command Number
+``wValue``         Subcommand Number (16 Bit) or 0 if not used
+``wIndex``         USB Interface Index (0 for device commands)
+``wLength``        * Host to Device - Number of bytes to transmit
+                   * Device to Host - Maximum Number of bytes to
+                     receive. If the device send less. Commom ZLP
+                     semantics are used.
+=================  =====================================================
+
+Error Handling
+--------------
+
+The device indicates failed control commands by stalling the
+pipe.
+
+Device Commands
+---------------
+
+UCAN_DEVICE_GET_FW_STRING
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*Dev2Host; optional*
+
+Request the device firmware string.
+
+
+Interface Commands
+------------------
+
+UCAN_COMMAND_START
+~~~~~~~~~~~~~~~~~~
+
+*Host2Dev; mandatory*
+
+Bring the CAN interface up.
+
+Payload Format
+  ``ucan_ctl_payload_t.cmd_start``
+
+====  ============================
+mode  or mask of ``UCAN_MODE_*``
+====  ============================
+
+UCAN_COMMAND_STOP
+~~~~~~~~~~~~~~~~~~
+
+*Host2Dev; mandatory*
+
+Stop the CAN interface
+
+Payload Format
+  *empty*
+
+UCAN_COMMAND_RESET
+~~~~~~~~~~~~~~~~~~
+
+*Host2Dev; mandatory*
+
+Reset the CAN controller (including error counters)
+
+Payload Format
+  *empty*
+
+UCAN_COMMAND_GET
+~~~~~~~~~~~~~~~~
+
+*Host2Dev; mandatory*
+
+Get Information from the Device
+
+Subcommands
+^^^^^^^^^^^
+
+UCAN_COMMAND_GET_INFO
+  Request the device information structure ``ucan_ctl_payload_t.device_info``.
+
+  See the ``device_info`` field for details, and
+  ``uapi/linux/can/netlink.h`` for an explanation of the
+  ``can_bittiming fields``.
+
+  Payload Format
+    ``ucan_ctl_payload_t.device_info``
+
+UCAN_COMMAND_GET_PROTOCOL_VERSION
+
+  Request the device protocol version
+  ``ucan_ctl_payload_t.protocol_version``. The current protocol version is 3.
+
+  Payload Format
+    ``ucan_ctl_payload_t.protocol_version``
+
+.. note:: Devices that do not implement this command use the old
+          protocol version 1
+
+UCAN_COMMAND_SET_BITTIMING
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*Host2Dev; mandatory*
+
+Setup bittiming by sending the the structure
+``ucan_ctl_payload_t.cmd_set_bittiming`` (see ``struct bittiming`` for
+details)
+
+Payload Format
+  ``ucan_ctl_payload_t.cmd_set_bittiming``.
+
+UCAN_SLEEP/WAKE
+~~~~~~~~~~~~~~~
+
+*Host2Dev; optional*
+
+Configure sleep and wake modes. Not yet supported by the driver.
+
+UCAN_FILTER
+~~~~~~~~~~~
+
+*Host2Dev; optional*
+
+Setup hardware CAN filters. Not yet supported by the driver.
+
+Allowed interface commands
+--------------------------
+
+==================  ===================  ==================
+Legal Device State  Command              New Device State
+==================  ===================  ==================
+stopped             SET_BITTIMING        stopped
+stopped             START                started
+started             STOP or RESET        stopped
+stopped             STOP or RESET        stopped
+started             RESTART              started
+any                 GET                  *no change*
+==================  ===================  ==================
+
+IN Message Format
+=================
+
+A data packet on the USB IN endpoint contains one or more
+``ucan_message_in`` values. If multiple messages are batched in a USB
+data packet, the ``len`` field can be used to jump to the next
+``ucan_message_in`` value (take care to sanity-check the ``len`` value
+against the actual data size).
+
+.. _can_ucan_in_message_len:
+
+``len`` field
+-------------
+
+Each ``ucan_message_in`` must be aligned to a 4-byte boundary (relative
+to the start of the start of the data buffer). That means that there
+may be padding bytes between multiple ``ucan_message_in`` values:
+
+.. code::
+
+    +----------------------------+ < 0
+    |                            |
+    |   struct ucan_message_in   |
+    |                            |
+    +----------------------------+ < len
+              [padding]
+    +----------------------------+ < round_up(len, 4)
+    |                            |
+    |   struct ucan_message_in   |
+    |                            |
+    +----------------------------+
+                [...]
+
+``type`` field
+--------------
+
+The ``type`` field specifies the type of the message.
+
+UCAN_IN_RX
+~~~~~~~~~~
+
+``subtype``
+  zero
+
+Data received from the CAN bus (ID + payload).
+
+UCAN_IN_TX_COMPLETE
+~~~~~~~~~~~~~~~~~~~
+
+``subtype``
+  zero
+
+The CAN device has sent a message to the CAN bus. It answers with a
+list of of tuples <echo-ids, flags>.
+
+The echo-id identifies the frame from (echos the id from a previous
+UCAN_OUT_TX message). The flag indicates the result of the
+transmission. Whereas a set Bit 0 indicates success. All other bits
+are reserved and set to zero.
+
+Flow Control
+------------
+
+When receiving CAN messages there is no flow control on the USB
+buffer. The driver has to handle inbound message quickly enough to
+avoid drops. I case the device buffer overflow the condition is
+reported by sending corresponding error frames (see
+:ref:`can_ucan_error_handling`)
+
+
+OUT Message Format
+==================
+
+A data packet on the USB OUT endpoint contains one or more ``struct
+ucan_message_out`` values. If multiple messages are batched into one
+data packet, the device uses the ``len`` field to jump to the next
+ucan_message_out value. Each ucan_message_out must be aligned to 4
+bytes (relative to the start of the data buffer). The mechanism is
+same as described in :ref:`can_ucan_in_message_len`.
+
+.. code::
+
+    +----------------------------+ < 0
+    |                            |
+    |   struct ucan_message_out  |
+    |                            |
+    +----------------------------+ < len
+              [padding]
+    +----------------------------+ < round_up(len, 4)
+    |                            |
+    |   struct ucan_message_out  |
+    |                            |
+    +----------------------------+
+                [...]
+
+``type`` field
+--------------
+
+In protocol version 3 only ``UCAN_OUT_TX`` is defined, others are used
+only by legacy devices (protocol version 1).
+
+UCAN_OUT_TX
+~~~~~~~~~~~
+``subtype``
+  echo id to be replied within a CAN_IN_TX_COMPLETE message
+
+Transmit a CAN frame. (parameters: ``id``, ``data``)
+
+Flow Control
+------------
+
+When the device outbound buffers are full it starts sending *NAKs* on
+the *OUT* pipe until more buffers are available. The driver stops the
+queue when a certain threshold of out packets are incomplete.
+
+.. _can_ucan_error_handling:
+
+CAN Error Handling
+==================
+
+If error reporting is turned on the device encodes errors into CAN
+error frames (see ``uapi/linux/can/error.h``) and sends it using the
+IN endpoint. The driver updates its error statistics and forwards
+it.
+
+Although UCAN devices can suppress error frames completely, in Linux
+the driver is always interested. Hence, the device is always started with
+the ``UCAN_MODE_BERR_REPORT`` set. Filtering those messages for the
+user space is done by the driver.
+
+Bus OFF
+-------
+
+- The device does not recover from bus of automatically.
+- Bus OFF is indicated by an error frame (see ``uapi/linux/can/error.h``)
+- Bus OFF recovery is started by ``UCAN_COMMAND_RESTART``
+- Once Bus OFF recover is completed the device sends an error frame
+  indicating that it is on ERROR-ACTIVE state.
+- During Bus OFF no frames are sent by the device.
+- During Bus OFF transmission requests from the host are completed
+  immediately with the success bit left unset.
+
+Example Conversation
+====================
+
+#) Device is connected to USB
+#) Host sends command ``UCAN_COMMAND_RESET``, subcmd 0
+#) Host sends command ``UCAN_COMMAND_GET``, subcmd ``UCAN_COMMAND_GET_INFO``
+#) Device sends ``UCAN_IN_DEVICE_INFO``
+#) Host sends command ``UCAN_OUT_SET_BITTIMING``
+#) Host sends command ``UCAN_COMMAND_START``, subcmd 0, mode ``UCAN_MODE_BERR_REPORT``
diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst
index 884a26145f20..fcd710f2cc7a 100644
--- a/Documentation/networking/index.rst
+++ b/Documentation/networking/index.rst
@@ -10,6 +10,7 @@ Contents:
    af_xdp
    batman-adv
    can
+   can_ucan_protocol
    dpaa2/index
    e100
    e1000