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Subject[PATCH v4] can, tty: elmcan CAN/ldisc driver for ELM327 based OBD-II adapters
Date
This is the elmcan driver. It does a surprisingly good job at turning
ELM327 based OBD-II interfaces into cheap CAN interfaces for simple
homebrew projects.

Please see the included documentation for details and limitations:
Documentation/networking/device_drivers/can/elmcan.rst

Cc: linux-can <linux-can@vger.kernel.org>
Signed-off-by: Max Staudt <max@enpas.org>
---
Many thanks to Greg, Marc, Vincent for reviewing v3!

I've CC'd you hoping you'd check whether you are happy with the changes.
Please do let me know.


Changes in v4:
- Rebased on top of v5.18-rc5
- Simplified TTY locking.
The ldisc layer already blocks our ldisc ops from running concurrently.
No elm_get(), no RCU are needed, except locking against the TX worker.
- Removed .hangup() ldisc op which only called .close().
The ldisc layer calls .close() in a good place anyway.
- Restart on netdev down/up, even after UART failure.
This is in line with Marc's line of thinking, and there was no
good reason not to implement it. It also cleaned up the code.
- hw_failure is now uart_side_failure and shutdown looks closer to es58x.
- Clarified memory/string comparisons.
One helper function remains, but it's hopefully clear now :)
- lockdep_assert_held() instead of comments.
- Cleaned up types in struct elmcan and used pahole to pack it.
unsigned instead of int, u8 instead of char, ...
- The TX buffer is now a static part of struct elmcan. No more kmalloc().
- Removed dummy mailbox_read() for rx_offload.
by using can_rx_offload_add_manual() instead of can_rx_offload_add_fifo().
- netif_wake_queue() is moved to happen as late as possible.
Wake when the ELM327 is going into monitoring mode, not every time
after flushing whatever UART buffer we were TX'ing.
- Use alloc_can_skb() and avoid late allocation and copy.
- elmcan_netdev_start_xmit(): Used can_dropped_invalid_skb().
- Replaced ->can_dlc with ->len.
- Clarified size of local TX buffer in elm327_handle_prompt().
- Renamed TODO_* to ELM327_TX_DO_* and ELM_* to ELM327_STATE_*.
- Minor string and other cleanups.
pr_fmt, MODULE_*, unnecessary checks, ...
- Clarified file header.

Changes in v3:
- Now depends on c2faf737abfb for new ldisc number 30.
- Eliminated hardcoded string lengths (GCC will work its magic).
- Emit generic error frames if an error message couldn't be parsed.
- Silence driver startup and init (but still announce ldattach).
- Cleaned up comments, strings, readme.
- Removed sole module option "accept_flaky_uart".
I likely had EMI in earlier testing, which is gone now.
This means we can stay strict, unless anyone objects.

Changes in v2:
- Moved to SocketCAN's rx-offload wrapper for NAPI, thus avoiding
packets being reordered.
- Updated TTY ldisc code for Linux v5.17-rc3. A lot of cleanup has
happened there lately.
- netif_stop_queue() is called earlier in _netdev_close().
- Minor cleanup: More helpful strings and return values.
---
.../networking/device_drivers/can/elmcan.rst | 325 +++++
.../networking/device_drivers/can/index.rst | 1 +
MAINTAINERS | 7 +
drivers/net/can/Kconfig | 17 +
drivers/net/can/Makefile | 1 +
drivers/net/can/elmcan.c | 1144 +++++++++++++++++
include/uapi/linux/tty.h | 3 +-
7 files changed, 1497 insertions(+), 1 deletion(-)
create mode 100644 Documentation/networking/device_drivers/can/elmcan.rst
create mode 100644 drivers/net/can/elmcan.c

diff --git a/Documentation/networking/device_drivers/can/elmcan.rst b/Documentation/networking/device_drivers/can/elmcan.rst
new file mode 100644
index 000000000000..b33a4b7da772
--- /dev/null
+++ b/Documentation/networking/device_drivers/can/elmcan.rst
@@ -0,0 +1,325 @@
+.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause)
+
+ELM327 driver for Linux SocketCAN
+==================================
+
+Authors
+--------
+
+Max Staudt <max@enpas.org>
+
+
+
+Motivation
+-----------
+
+This driver aims to lower the initial cost for hackers interested in
+working with CAN buses.
+
+CAN adapters are expensive, few, and far between.
+ELM327 interfaces are cheap and plentiful.
+Let's use ELM327s as CAN adapters.
+
+
+
+Introduction
+-------------
+
+This driver is an effort to turn abundant ELM327 based OBD interfaces
+into full fledged (as far as possible) CAN interfaces.
+
+Since the ELM327 was never meant to be a stand alone CAN controller,
+the driver has to switch between its modes as quickly as possible in
+order to fake full-duplex operation.
+
+As such, elmcan is a best effort driver. However, this is more than
+enough to implement simple request-response protocols (such as OBD II),
+and to monitor broadcast messages on a bus (such as in a vehicle).
+
+Most ELM327s come as nondescript serial devices, attached via USB or
+Bluetooth. The driver cannot recognize them by itself, and as such it
+is up to the user to attach it in form of a TTY line discipline
+(similar to PPP, SLIP, slcan, ...).
+
+This driver is meant for ELM327 versions 1.4b and up, see below for
+known limitations in older controllers and clones.
+
+
+
+Data sheet
+-----------
+
+The official data sheets can be found at ELM electronics' home page:
+
+ https://www.elmelectronics.com/
+
+
+
+How to check the controller version
+------------------------------------
+
+Use a terminal program to attach to the controller.
+The default settings are 38400 baud/s, 8 data bits, no parity, 1 stopbit.
+
+After issuing the "``AT WS``" command, the controller will respond with
+its version::
+
+ >AT WS
+
+
+ ELM327 v1.4b
+
+ >
+
+Note that clones may claim to be any version they like.
+It is not indicative of their actual feature set.
+
+
+
+How to attach the line discipline
+----------------------------------
+
+Every ELM327 chip is factory programmed to operate at a serial setting
+of 38400 baud/s, 8 data bits, no parity, 1 stopbit.
+
+The line discipline can be attached on a command prompt as follows::
+
+ sudo ldattach \
+ --debug \
+ --speed 38400 \
+ --eightbits \
+ --noparity \
+ --onestopbit \
+ --iflag -ICRNL,INLCR,-IXOFF \
+ 30 \
+ /dev/ttyUSB0
+
+To change the ELM327's serial settings, please refer to its data
+sheet. This needs to be done before attaching the line discipline.
+
+Once the ldisc is attached, the CAN interface starts out unconfigured.
+Set the speed before starting it:
+
+ # The interface needs to be down to change parameters
+ sudo ip link set can0 down
+ sudo ip link set can0 type can bitrate 500000
+ sudo ip link set can0 up
+
+500000 bit/s is a common rate for OBD-II diagnostics.
+If you're connecting straight to a car's OBD port, this is the speed
+that most cars (but not all!) expect.
+
+After this, you can set out as usual with candump, cansniffer, etc.
+
+
+
+Known limitations of the controller
+------------------------------------
+
+- Clone devices ("v1.5" and others)
+
+ Sending RTR frames is not supported and will be dropped silently.
+
+ Receiving RTR with DLC 8 will appear to be a regular frame with
+ the last received frame's DLC and payload.
+
+ "``AT CSM``" not supported, thus no ACK-ing frames while listening:
+ "``AT MA``" will always be silent. However, immediately after
+ sending a frame, the ELM327 will be in "receive reply" mode, in
+ which it *does* ACK any received frames. Once the bus goes silent
+ or an error occurs (such as BUFFER FULL), the ELM327 will end reply
+ reception mode on its own and elmcan will fall back to "``AT MA``"
+ in order to keep monitoring the bus.
+
+
+- All versions
+
+ No full duplex operation is supported. The driver will switch
+ between input/output mode as quickly as possible.
+
+ The length of outgoing RTR frames cannot be set. In fact, some
+ clones (tested with one identifying as "``v1.5``") are unable to
+ send RTR frames at all.
+
+ We don't have a way to get real-time notifications on CAN errors.
+ While there is a command (``AT CS``) to retrieve some basic stats,
+ we don't poll it as it would force us to interrupt reception mode.
+
+
+- Versions prior to 1.4b
+
+ These versions do not send CAN ACKs when in monitoring mode (AT MA).
+ However, they do send ACKs while waiting for a reply immediately
+ after sending a frame. The driver maximizes this time to make the
+ controller as useful as possible.
+
+ Starting with version 1.4b, the ELM327 supports the "``AT CSM``"
+ command, and the "listen-only" CAN option will take effect.
+
+
+- Versions prior to 1.4
+
+ These chips do not support the "``AT PB``" command, and thus cannot
+ change bitrate or SFF/EFF mode on-the-fly. This will have to be
+ programmed by the user before attaching the line discipline. See the
+ data sheet for details.
+
+
+- Versions prior to 1.3
+
+ These chips cannot be used at all with elmcan. They do not support
+ the "``AT D1``" command, which is necessary to avoid parsing conflicts
+ on incoming data, as well as distinction of RTR frame lengths.
+
+ Specifically, this allows for easy distinction of SFF and EFF
+ frames, and to check whether frames are complete. While it is possible
+ to deduce the type and length from the length of the line the ELM327
+ sends us, this method fails when the ELM327's UART output buffer
+ overruns. It may abort sending in the middle of the line, which will
+ then be mistaken for something else.
+
+
+
+Known limitations of the driver
+--------------------------------
+
+- No 8/7 timing.
+
+ ELM327 can only set CAN bitrates that are of the form 500000/n, where
+ n is an integer divisor.
+ However there is an exception: With a separate flag, it may set the
+ speed to be 8/7 of the speed indicated by the divisor.
+ This mode is not currently implemented.
+
+- No evaluation of command responses.
+
+ The ELM327 will reply with OK when a command is understood, and with ?
+ when it is not. The driver does not currently check this, and simply
+ assumes that the chip understands every command.
+ The driver is built such that functionality degrades gracefully
+ nevertheless. See the section on known limitations of the controller.
+
+- No use of hardware CAN ID filtering
+
+ An ELM327's UART sending buffer will easily overflow on heavy CAN bus
+ load, resulting in the "``BUFFER FULL``" message. Using the hardware
+ filters available through "``AT CF xxx``" and "``AT CM xxx``" would be
+ helpful here, however SocketCAN does not currently provide a facility
+ to make use of such hardware features.
+
+
+
+Communication example
+----------------------
+
+This is a short and incomplete introduction on how to talk to an ELM327.
+
+
+The ELM327 has two modes:
+
+- Command mode
+- Reception mode
+
+In command mode, it expects one command per line, terminated by CR.
+By default, the prompt is a "``>``", after which a command can be
+entered::
+
+ >ATE1
+ OK
+ >
+
+The init script in the driver switches off several configuration options
+that are only meaningful in the original OBD scenario the chip is meant
+for, and are actually a hindrance for elmcan.
+
+
+When a command is not recognized, such as by an older version of the
+ELM327, a question mark is printed as a response instead of OK::
+
+ >ATUNKNOWN
+ ?
+ >
+
+At present, elmcan does not evaluate this response and silently assumes
+that all commands are recognized. It is structured such that it will
+degrade gracefully when a command is unknown. See the sections above on
+known limitations for details.
+
+
+When a CAN frame is to be sent, the target address is configured, after
+which the frame is sent as a command that consists of the data's hex
+dump::
+
+ >ATSH123
+ OK
+ >DEADBEEF12345678
+ OK
+ >
+
+The above interaction sends the frame "``DE AD BE EF 12 34 56 78``" with
+the 11 bit CAN ID ``0x123``.
+For this to function, the controller must be configured for 11 bit CAN
+ID sending mode (using "``AT PB``", see code or datasheet).
+
+
+Once a frame has been sent and wait-for-reply mode is on (``ATR1``,
+configured on ``listen-only=off``), or when the reply timeout expires and
+the driver sets the controller into monitoring mode (``ATMA``), the ELM327
+will send one line for each received CAN frame, consisting of CAN ID,
+DLC, and data::
+
+ 123 8 DEADBEEF12345678
+
+For 29 bit CAN frames, the address format is slightly different, which
+elmcan uses to tell the two apart::
+
+ 12 34 56 78 8 DEADBEEF12345678
+
+The ELM327 will receive both 11 and 29 bit frames - the current CAN
+config (``ATPB``) does not matter.
+
+
+If the ELM327's internal UART sending buffer runs full, it will abort
+the monitoring mode, print "BUFFER FULL" and drop back into command
+mode. Note that in this case, unlike with other error messages, the
+error message may appear on the same line as the last (usually
+incomplete) data frame::
+
+ 12 34 56 78 8 DEADBEEF123 BUFFER FULL
+
+
+
+Rationale behind the chosen configuration
+------------------------------------------
+
+``AT E1``
+ Echo on
+
+ We need this to be able to get a prompt reliably.
+
+``AT S1``
+ Spaces on
+
+ We need this to distinguish 11/29 bit CAN addresses received.
+
+ Note:
+ We can usually do this using the line length (odd/even),
+ but this fails if the line is not transmitted fully to
+ the host (BUFFER FULL).
+
+``AT D1``
+ DLC on
+
+ We need this to tell the "length" of RTR frames.
+
+
+
+A note on CAN bus termination
+------------------------------
+
+Your adapter may have resistors soldered in which are meant to terminate
+the bus. This is correct when it is plugged into a OBD-II socket, but
+not helpful when trying to tap into the middle of an existing CAN bus.
+
+If communications don't work with the adapter connected, check for the
+termination resistors on its PCB and try removing them.
diff --git a/Documentation/networking/device_drivers/can/index.rst b/Documentation/networking/device_drivers/can/index.rst
index 58b6e0ad3030..e3f2be735aef 100644
--- a/Documentation/networking/device_drivers/can/index.rst
+++ b/Documentation/networking/device_drivers/can/index.rst
@@ -10,6 +10,7 @@ Contents:
.. toctree::
:maxdepth: 2

+ elmcan
freescale/flexcan

.. only:: subproject and html
diff --git a/MAINTAINERS b/MAINTAINERS
index edc96cdb85e8..8a1f2bf82407 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7218,6 +7218,13 @@ L: netdev@vger.kernel.org
S: Maintained
F: drivers/net/ethernet/ibm/ehea/

+ELM327 CAN NETWORK DRIVER
+M: Max Staudt <max@enpas.org>
+L: linux-can@vger.kernel.org
+S: Maintained
+F: Documentation/networking/device_drivers/can/elmcan.rst
+F: drivers/net/can/elmcan.c
+
EM28XX VIDEO4LINUX DRIVER
M: Mauro Carvalho Chehab <mchehab@kernel.org>
L: linux-media@vger.kernel.org
diff --git a/drivers/net/can/Kconfig b/drivers/net/can/Kconfig
index fff259247d52..226bd00fc048 100644
--- a/drivers/net/can/Kconfig
+++ b/drivers/net/can/Kconfig
@@ -180,6 +180,23 @@ source "drivers/net/can/softing/Kconfig"
source "drivers/net/can/spi/Kconfig"
source "drivers/net/can/usb/Kconfig"

+config CAN_ELMCAN
+ tristate "Serial / USB serial ELM327 based OBD-II Interfaces (elmcan)"
+ depends on TTY
+ help
+ CAN driver for several 'low cost' OBD-II interfaces based on the
+ ELM327 OBD-II interpreter chip.
+
+ This is a best effort driver - the ELM327 interface was never
+ designed to be used as a standalone CAN interface. However, it can
+ still be used for simple request-response protocols (such as OBD II),
+ and to monitor broadcast messages on a bus (such as in a vehicle).
+
+ Please refer to the documentation for information on how to use it:
+ Documentation/networking/device_drivers/can/elmcan.rst
+
+ If this driver is built as a module, it will be called elmcan.
+
endif

config CAN_DEBUG_DEVICES
diff --git a/drivers/net/can/Makefile b/drivers/net/can/Makefile
index 1e660afcb61b..c25a0f8a397b 100644
--- a/drivers/net/can/Makefile
+++ b/drivers/net/can/Makefile
@@ -6,6 +6,7 @@
obj-$(CONFIG_CAN_VCAN) += vcan.o
obj-$(CONFIG_CAN_VXCAN) += vxcan.o
obj-$(CONFIG_CAN_SLCAN) += slcan.o
+obj-$(CONFIG_CAN_ELMCAN) += elmcan.o

obj-y += dev/
obj-y += rcar/
diff --git a/drivers/net/can/elmcan.c b/drivers/net/can/elmcan.c
new file mode 100644
index 000000000000..291a3257fae9
--- /dev/null
+++ b/drivers/net/can/elmcan.c
@@ -0,0 +1,1144 @@
+// SPDX-License-Identifier: GPL-2.0
+/* ELM327 based CAN interface driver (tty line discipline)
+ *
+ * This driver started as a derivative of linux/drivers/net/can/slcan.c
+ * and my thanks go to the original authors for their inspiration.
+ *
+ * elmcan.c Author : Max Staudt <max-linux@enpas.org>
+ * slcan.c Author : Oliver Hartkopp <socketcan@hartkopp.net>
+ * slip.c Authors : Laurence Culhane <loz@holmes.demon.co.uk>
+ * Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
+ */
+
+#define pr_fmt(fmt) "elmcan: " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/ctype.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/if_ether.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/lockdep.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/tty.h>
+#include <linux/tty_ldisc.h>
+#include <linux/workqueue.h>
+
+#include <uapi/linux/tty.h>
+
+#include <linux/can.h>
+#include <linux/can/dev.h>
+#include <linux/can/error.h>
+#include <linux/can/led.h>
+#include <linux/can/rx-offload.h>
+
+#define ELM327_NAPI_WEIGHT 4
+
+#define ELM327_SIZE_RXBUF 224
+#define ELM327_SIZE_TXBUF 32
+
+#define ELM327_CAN_CONFIG_SEND_SFF 0x8000
+#define ELM327_CAN_CONFIG_VARIABLE_DLC 0x4000
+#define ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF 0x2000
+#define ELM327_CAN_CONFIG_BAUDRATE_MULT_8_7 0x1000
+
+#define ELM327_DUMMY_CHAR 'y'
+#define ELM327_DUMMY_STRING "y"
+#define ELM327_READY_CHAR '>'
+
+/* Bits in elm->cmds_todo */
+enum elm327_to_to_do_bits {
+ ELM327_TX_DO_CAN_DATA = 0,
+ ELM327_TX_DO_CANID_11BIT,
+ ELM327_TX_DO_CANID_29BIT_LOW,
+ ELM327_TX_DO_CANID_29BIT_HIGH,
+ ELM327_TX_DO_CAN_CONFIG_PART2,
+ ELM327_TX_DO_CAN_CONFIG,
+ ELM327_TX_DO_RESPONSES,
+ ELM327_TX_DO_SILENT_MONITOR,
+ ELM327_TX_DO_INIT
+};
+
+struct elmcan {
+ /* This must be the first member when using alloc_candev() */
+ struct can_priv can;
+
+ struct can_rx_offload offload;
+
+ /* TTY buffers */
+ u8 rxbuf[ELM327_SIZE_RXBUF];
+ u8 txbuf[ELM327_SIZE_TXBUF] ____cacheline_aligned;
+
+ /* TTY buffer accounting */
+ struct work_struct tx_work; /* Flushes TTY TX buffer */
+ u8 *txhead; /* Next TX byte */
+ unsigned txleft; /* Bytes left to TX */
+ int rxfill; /* Bytes already RX'd in buffer */
+
+ /* TTY and netdev devices that we're bridging */
+ struct tty_struct *tty;
+ struct net_device *dev;
+
+ /* Per-channel lock */
+ spinlock_t lock;
+
+ /* State machine */
+ enum {
+ ELM327_STATE_NOTINIT = 0,
+ ELM327_STATE_GETDUMMYCHAR,
+ ELM327_STATE_GETPROMPT,
+ ELM327_STATE_RECEIVING,
+ } state;
+
+ /* Things we have yet to send */
+ char **next_init_cmd;
+ unsigned long cmds_todo;
+
+ /* The CAN frame and config the ELM327 is sending/using,
+ * or will send/use after finishing all cmds_todo
+ */
+ struct can_frame can_frame_to_send;
+ u16 can_config;
+ u8 can_bitrate_divisor;
+
+ /* Parser state */
+ bool drop_next_line;
+
+ /* Stop the channel on UART side hardware failure, e.g. stray
+ * characters or neverending lines. This may be caused by bad
+ * UART wiring, a bad ELM327, a bad UART bridge...
+ * Once this is true, nothing will be sent to the TTY.
+ */
+ bool uart_side_failure;
+};
+
+static inline void elm327_uart_side_failure(struct elmcan *elm);
+
+static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
+{
+ int written;
+
+ lockdep_assert_held(elm->lock);
+
+ if (elm->uart_side_failure)
+ return;
+
+ memcpy(elm->txbuf, buf, len);
+
+ written = elm->tty->ops->write(elm->tty, elm->txbuf, len);
+ if (written < 0) {
+ netdev_err(elm->dev,
+ "Failed to write to tty %s.\n",
+ elm->tty->name);
+ elm327_uart_side_failure(elm);
+ return;
+ }
+
+ elm->txleft = len - written;
+ elm->txhead = elm->txbuf + written;
+
+ if (elm->txleft)
+ set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+}
+
+/* Take the ELM327 out of almost any state and back into command mode.
+ * We send ELM327_DUMMY_CHAR which will either abort any running
+ * operation, or be echoed back to us in case we're already in command
+ * mode.
+ */
+static void elm327_kick_into_cmd_mode(struct elmcan *elm)
+{
+ lockdep_assert_held(elm->lock);
+
+ if (elm->state != ELM327_STATE_GETDUMMYCHAR &&
+ elm->state != ELM327_STATE_GETPROMPT) {
+ elm327_send(elm, ELM327_DUMMY_STRING, 1);
+
+ elm->state = ELM327_STATE_GETDUMMYCHAR;
+ }
+}
+
+/* Schedule a CAN frame and necessary config changes to be sent to the TTY. */
+static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
+{
+ lockdep_assert_held(elm->lock);
+
+ /* Schedule any necessary changes in ELM327's CAN configuration */
+ if (elm->can_frame_to_send.can_id != frame->can_id) {
+ /* Set the new CAN ID for transmission. */
+ if ((frame->can_id & CAN_EFF_FLAG) ^
+ (elm->can_frame_to_send.can_id & CAN_EFF_FLAG)) {
+ elm->can_config = (frame->can_id & CAN_EFF_FLAG
+ ? 0
+ : ELM327_CAN_CONFIG_SEND_SFF)
+ | ELM327_CAN_CONFIG_VARIABLE_DLC
+ | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
+ | elm->can_bitrate_divisor;
+
+ set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
+ }
+
+ if (frame->can_id & CAN_EFF_FLAG) {
+ clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
+ set_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
+ set_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
+ } else {
+ set_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
+ clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
+ clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
+ }
+ }
+
+ /* Schedule the CAN frame itself. */
+ elm->can_frame_to_send = *frame;
+ set_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo);
+
+ elm327_kick_into_cmd_mode(elm);
+}
+
+/* ELM327 initialisation sequence.
+ * The line length is limited by the buffer in elm327_handle_prompt().
+ */
+static char *elm327_init_script[] = {
+ "AT WS\r", /* v1.0: Warm Start */
+ "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
+ "AT M0\r", /* v1.0: Memory Off */
+ "AT AL\r", /* v1.0: Allow Long messages */
+ "AT BI\r", /* v1.0: Bypass Initialisation */
+ "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
+ "AT CFC0\r", /* v1.0: CAN Flow Control Off */
+ "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
+ "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
+ "AT E1\r", /* v1.0: Echo On */
+ "AT H1\r", /* v1.0: Headers On */
+ "AT L0\r", /* v1.0: Linefeeds Off */
+ "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
+ "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
+ "AT AT0\r", /* v1.2: Adaptive Timing Off */
+ "AT D1\r", /* v1.3: Print DLC On */
+ "AT S1\r", /* v1.3: Spaces On */
+ "AT TP B\r", /* v1.0: Try Protocol B */
+ NULL
+};
+
+static void elm327_init(struct elmcan *elm)
+{
+ lockdep_assert_held(elm->lock);
+
+ elm->state = ELM327_STATE_NOTINIT;
+ elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
+ elm->rxfill = 0;
+ elm->drop_next_line = 0;
+
+ /* We can only set the bitrate as a fraction of 500000.
+ * The bit timing constants in elmcan_bittiming_const will
+ * limit the user to the right values.
+ */
+ elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
+ elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
+ | ELM327_CAN_CONFIG_VARIABLE_DLC
+ | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
+ | elm->can_bitrate_divisor;
+
+ /* Configure ELM327 and then start monitoring */
+ elm->next_init_cmd = &elm327_init_script[0];
+ set_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
+ set_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
+ set_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo);
+ set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
+
+ elm327_kick_into_cmd_mode(elm);
+}
+
+static void elm327_feed_frame_to_netdev(struct elmcan *elm,
+ struct sk_buff *skb)
+{
+ lockdep_assert_held(elm->lock);
+
+ if (!netif_running(elm->dev))
+ return;
+
+ /* Queue for NAPI pickup.
+ * rx-offload will update stats and LEDs for us.
+ */
+ if (can_rx_offload_queue_tail(&elm->offload, skb))
+ elm->dev->stats.rx_fifo_errors++;
+
+ /* Wake NAPI */
+ can_rx_offload_irq_finish(&elm->offload);
+}
+
+/* Called when we're out of ideas and just want it all to end. */
+static inline void elm327_uart_side_failure(struct elmcan *elm)
+{
+ struct can_frame *frame;
+ struct sk_buff *skb;
+
+ lockdep_assert_held(elm->lock);
+
+ elm->uart_side_failure = true;
+
+ elm->can.can_stats.bus_off++;
+ netif_stop_queue(elm->dev);
+ elm->can.state = CAN_STATE_BUS_OFF;
+ can_bus_off(elm->dev);
+
+ netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
+
+ skb = alloc_can_err_skb(elm->dev, &frame);
+ if (!skb)
+ return;
+
+ frame->can_id |= CAN_ERR_BUSOFF;
+ elm327_feed_frame_to_netdev(elm, skb);
+}
+
+/* Compare buffer to string length, then compare buffer to fixed string.
+ * This ensures two things:
+ * - It flags cases where the fixed string is only the start of the
+ * buffer, rather than exactly all of it.
+ * - It avoids byte comparisons in case the length doesn't match.
+ *
+ * strncmp() cannot be used here because it accepts the following wrong case:
+ * strncmp("CAN ER", "CAN ERROR", 6);
+ * This must fail, hence this helper function.
+ */
+static inline int check_len_then_cmp(const u8 *mem, size_t mem_len, const char *str)
+{
+ size_t str_len = strlen(str);
+
+ return (mem_len == str_len) && !memcmp(mem, str, str_len);
+}
+
+static void elm327_parse_error(struct elmcan *elm, size_t len)
+{
+ struct can_frame *frame;
+ struct sk_buff *skb;
+
+ lockdep_assert_held(elm->lock);
+
+ skb = alloc_can_err_skb(elm->dev, &frame);
+ if (!skb)
+ /* It's okay to return here:
+ * The outer parsing loop will drop this UART buffer.
+ */
+ return;
+
+ /* Filter possible error messages based on length of RX'd line */
+ if (check_len_then_cmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
+ netdev_err(elm->dev,
+ "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
+ } else if (check_len_then_cmp(elm->rxbuf, len, "BUFFER FULL")) {
+ /* This will only happen if the last data line was complete.
+ * Otherwise, elm327_parse_frame() will heuristically
+ * emit this kind of error frame instead.
+ */
+ frame->can_id |= CAN_ERR_CRTL;
+ frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
+ } else if (check_len_then_cmp(elm->rxbuf, len, "BUS ERROR")) {
+ frame->can_id |= CAN_ERR_BUSERROR;
+ } else if (check_len_then_cmp(elm->rxbuf, len, "CAN ERROR")) {
+ frame->can_id |= CAN_ERR_PROT;
+ } else if (check_len_then_cmp(elm->rxbuf, len, "<RX ERROR")) {
+ frame->can_id |= CAN_ERR_PROT;
+ } else if (check_len_then_cmp(elm->rxbuf, len, "BUS BUSY")) {
+ frame->can_id |= CAN_ERR_PROT;
+ frame->data[2] = CAN_ERR_PROT_OVERLOAD;
+ } else if (check_len_then_cmp(elm->rxbuf, len, "FB ERROR")) {
+ frame->can_id |= CAN_ERR_PROT;
+ frame->data[2] = CAN_ERR_PROT_TX;
+ } else if (len == 5 && !memcmp(elm->rxbuf, "ERR", 3)) {
+ /* ERR is followed by two digits, hence line length 5 */
+ netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
+ elm->rxbuf[3], elm->rxbuf[4]);
+ frame->can_id |= CAN_ERR_CRTL;
+ } else {
+ /* Something else has happened.
+ * Maybe garbage on the UART line.
+ * Emit a generic error frame.
+ */
+ }
+
+ elm327_feed_frame_to_netdev(elm, skb);
+}
+
+/* Parse CAN frames coming as ASCII from ELM327.
+ * They can be of various formats:
+ *
+ * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
+ * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
+ *
+ * where D = DLC, PL = payload byte
+ *
+ * Instead of a payload, RTR indicates a remote request.
+ *
+ * We will use the spaces and line length to guess the format.
+ */
+static int elm327_parse_frame(struct elmcan *elm, size_t len)
+{
+ struct can_frame *frame;
+ struct sk_buff *skb;
+ int hexlen;
+ int datastart;
+ int i;
+
+ lockdep_assert_held(elm->lock);
+
+ skb = alloc_can_skb(elm->dev, &frame);
+ if (!skb)
+ return -ENOMEM;
+
+ /* Find first non-hex and non-space character:
+ * - In the simplest case, there is none.
+ * - For RTR frames, 'R' is the first non-hex character.
+ * - An error message may replace the end of the data line.
+ */
+ for (hexlen = 0; hexlen <= len; hexlen++) {
+ if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
+ elm->rxbuf[hexlen] != ' ') {
+ break;
+ }
+ }
+
+ /* Sanity check whether the line is really a clean hexdump,
+ * or terminated by an error message, or contains garbage.
+ */
+ if (hexlen < len &&
+ !isdigit(elm->rxbuf[hexlen]) &&
+ !isupper(elm->rxbuf[hexlen]) &&
+ '<' != elm->rxbuf[hexlen] &&
+ ' ' != elm->rxbuf[hexlen]) {
+ /* The line is likely garbled anyway, so bail.
+ * The main code will restart listening.
+ */
+ return -ENODATA;
+ }
+
+ /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
+ * No out-of-bounds access:
+ * We use the fact that we can always read from elm->rxbuf.
+ */
+ if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
+ elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
+ elm->rxbuf[13] == ' ') {
+ frame->can_id = CAN_EFF_FLAG;
+ datastart = 14;
+ } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
+ datastart = 6;
+ } else {
+ /* This is not a well-formatted data line.
+ * Assume it's an error message.
+ */
+ return -ENODATA;
+ }
+
+ if (hexlen < datastart) {
+ /* The line is too short to be a valid frame hex dump.
+ * Something interrupted the hex dump or it is invalid.
+ */
+ return -ENODATA;
+ }
+
+ /* From here on all chars up to buf[hexlen] are hex or spaces,
+ * at well-defined offsets.
+ */
+
+ /* Read CAN data length */
+ frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
+
+ /* Read CAN ID */
+ if (frame->can_id & CAN_EFF_FLAG) {
+ frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
+ | (hex_to_bin(elm->rxbuf[1]) << 24)
+ | (hex_to_bin(elm->rxbuf[3]) << 20)
+ | (hex_to_bin(elm->rxbuf[4]) << 16)
+ | (hex_to_bin(elm->rxbuf[6]) << 12)
+ | (hex_to_bin(elm->rxbuf[7]) << 8)
+ | (hex_to_bin(elm->rxbuf[9]) << 4)
+ | (hex_to_bin(elm->rxbuf[10]) << 0);
+ } else {
+ frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
+ | (hex_to_bin(elm->rxbuf[1]) << 4)
+ | (hex_to_bin(elm->rxbuf[2]) << 0);
+ }
+
+ /* Check for RTR frame */
+ if (elm->rxfill >= hexlen + 3 &&
+ !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
+ frame->can_id |= CAN_RTR_FLAG;
+ }
+
+ /* Is the line long enough to hold the advertised payload?
+ * Note: RTR frames have a DLC, but no actual payload.
+ */
+ if (!(frame->can_id & CAN_RTR_FLAG) &&
+ (hexlen < frame->len * 3 + datastart)) {
+ /* Incomplete frame.
+ * Probably the ELM327's RS232 TX buffer was full.
+ * Emit an error frame and exit.
+ */
+ frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
+ frame->len = CAN_ERR_DLC;
+ frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
+ elm327_feed_frame_to_netdev(elm, skb);
+
+ /* Signal failure to parse.
+ * The line will be re-parsed as an error line, which will fail.
+ * However, this will correctly drop the state machine back into
+ * command mode.
+ */
+ return -ENODATA;
+ }
+
+ /* Parse the data nibbles. */
+ for (i = 0; i < frame->len; i++) {
+ frame->data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
+ | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
+ }
+
+ /* Feed the frame to the network layer. */
+ elm327_feed_frame_to_netdev(elm, skb);
+
+ return 0;
+}
+
+static void elm327_parse_line(struct elmcan *elm, size_t len)
+{
+ lockdep_assert_held(elm->lock);
+
+ /* Skip empty lines */
+ if (!len)
+ return;
+
+ /* Skip echo lines */
+ if (elm->drop_next_line) {
+ elm->drop_next_line = 0;
+ return;
+ } else if (!memcmp(elm->rxbuf, "AT", 2)) {
+ return;
+ }
+
+ /* Regular parsing */
+ if (elm->state == ELM327_STATE_RECEIVING
+ && elm327_parse_frame(elm, len)) {
+ /* Parse an error line. */
+ elm327_parse_error(elm, len);
+
+ /* Start afresh. */
+ elm327_kick_into_cmd_mode(elm);
+ }
+}
+
+static void elm327_handle_prompt(struct elmcan *elm)
+{
+ struct can_frame *frame = &elm->can_frame_to_send;
+ /* Size this buffer for the largest ELM327 line we may generate,
+ * which is currently an 8 byte CAN frame's payload hexdump.
+ * Items in elm327_init_script must fit here, too!
+ */
+ char local_txbuf[sizeof("0102030405060708\r")];
+
+ lockdep_assert_held(elm->lock);
+
+ if (!elm->cmds_todo) {
+ /* Enter CAN monitor mode */
+ elm327_send(elm, "ATMA\r", 5);
+ elm->state = ELM327_STATE_RECEIVING;
+
+ /* We will be in the default state once this command is
+ * send, so enable the TX packet queue.
+ */
+ netif_wake_queue(elm->dev);
+
+ return;
+ }
+
+ /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
+ if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "%s",
+ *elm->next_init_cmd);
+
+ elm->next_init_cmd++;
+ if (!(*elm->next_init_cmd)) {
+ clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
+ /* Init finished. */
+ }
+
+ } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "ATCSM%i\r",
+ !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
+
+ } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "ATR%i\r",
+ !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
+
+ } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "ATPC\r");
+ set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
+
+ } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "ATPB%04X\r",
+ elm->can_config);
+
+ } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "ATCP%02X\r",
+ (frame->can_id & CAN_EFF_MASK) >> 24);
+
+ } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "ATSH%06X\r",
+ frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
+
+ } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "ATSH%03X\r",
+ frame->can_id & CAN_SFF_MASK);
+
+ } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
+ if (frame->can_id & CAN_RTR_FLAG) {
+ /* Send an RTR frame. Their DLC is fixed.
+ * Some chips don't send them at all.
+ */
+ snprintf(local_txbuf, sizeof(local_txbuf),
+ "ATRTR\r");
+ } else {
+ /* Send a regular CAN data frame */
+ int i;
+
+ for (i = 0; i < frame->len; i++) {
+ snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
+ "%02X",
+ frame->data[i]);
+ }
+
+ snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
+ "\r");
+ }
+
+ elm->drop_next_line = 1;
+ elm->state = ELM327_STATE_RECEIVING;
+
+ /* We will be in the default state once this command is
+ * send, so enable the TX packet queue.
+ */
+ netif_wake_queue(elm->dev);
+ }
+
+ elm327_send(elm, local_txbuf, strlen(local_txbuf));
+}
+
+static bool elm327_is_ready_char(char c)
+{
+ /* Bits 0xc0 are sometimes set (randomly), hence the mask.
+ * Probably bad hardware.
+ */
+ return (c & 0x3f) == ELM327_READY_CHAR;
+}
+
+static void elm327_drop_bytes(struct elmcan *elm, size_t i)
+{
+ lockdep_assert_held(elm->lock);
+
+ memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
+ elm->rxfill -= i;
+}
+
+static void elm327_parse_rxbuf(struct elmcan *elm)
+{
+ size_t len;
+ int i;
+
+ lockdep_assert_held(elm->lock);
+
+ switch (elm->state) {
+ case ELM327_STATE_NOTINIT:
+ elm->rxfill = 0;
+ break;
+
+ case ELM327_STATE_GETDUMMYCHAR:
+ {
+ /* Wait for 'y' or '>' */
+ for (i = 0; i < elm->rxfill; i++) {
+ if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
+ elm327_send(elm, "\r", 1);
+ elm->state = ELM327_STATE_GETPROMPT;
+ i++;
+ break;
+ } else if (elm327_is_ready_char(elm->rxbuf[i])) {
+ elm327_send(elm, ELM327_DUMMY_STRING, 1);
+ i++;
+ break;
+ }
+ }
+
+ elm327_drop_bytes(elm, i);
+
+ break;
+ }
+
+ case ELM327_STATE_GETPROMPT:
+ /* Wait for '>' */
+ if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
+ elm327_handle_prompt(elm);
+
+ elm->rxfill = 0;
+ break;
+
+ case ELM327_STATE_RECEIVING:
+ /* Find <CR> delimiting feedback lines. */
+ for (len = 0;
+ (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
+ len++) {
+ /* empty loop */
+ }
+
+ if (len == ELM327_SIZE_RXBUF) {
+ /* Line exceeds buffer. It's probably all garbage.
+ * Did we even connect at the right baud rate?
+ */
+ netdev_err(elm->dev,
+ "RX buffer overflow. Faulty ELM327 or UART?\n");
+ elm327_uart_side_failure(elm);
+ break;
+ } else if (len == elm->rxfill) {
+ if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
+ /* The ELM327's AT ST response timeout ran out,
+ * so we got a prompt.
+ * Clear RX buffer and restart listening.
+ */
+ elm->rxfill = 0;
+
+ elm327_handle_prompt(elm);
+ break;
+ }
+
+ /* No <CR> found - we haven't received a full line yet.
+ * Wait for more data.
+ */
+ break;
+ }
+
+ /* We have a full line to parse. */
+ elm327_parse_line(elm, len);
+
+ /* Remove parsed data from RX buffer. */
+ elm327_drop_bytes(elm, len + 1);
+
+ /* More data to parse? */
+ if (elm->rxfill)
+ elm327_parse_rxbuf(elm);
+ }
+}
+
+static int elmcan_netdev_open(struct net_device *dev)
+{
+ struct elmcan *elm = netdev_priv(dev);
+ int err;
+
+ spin_lock_bh(&elm->lock);
+
+ if (!elm->tty) {
+ spin_unlock_bh(&elm->lock);
+ return -ENODEV;
+ }
+
+ if (elm->uart_side_failure)
+ netdev_warn(elm->dev, "Reopening netdev after a UART side fault has been detected.\n");
+
+ /* Clear TTY buffers */
+ elm->rxfill = 0;
+ elm->txleft = 0;
+
+ /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
+ err = open_candev(dev);
+ if (err) {
+ spin_unlock_bh(&elm->lock);
+ return err;
+ }
+
+ elm327_init(elm);
+ spin_unlock_bh(&elm->lock);
+
+ err = can_rx_offload_add_manual(dev, &elm->offload, ELM327_NAPI_WEIGHT);
+ if (err) {
+ close_candev(dev);
+ return err;
+ }
+
+ can_rx_offload_enable(&elm->offload);
+
+ can_led_event(dev, CAN_LED_EVENT_OPEN);
+ elm->can.state = CAN_STATE_ERROR_ACTIVE;
+ netif_start_queue(dev);
+
+ return 0;
+}
+
+static int elmcan_netdev_close(struct net_device *dev)
+{
+ struct elmcan *elm = netdev_priv(dev);
+
+ /* Interrupt whatever the ELM327 is doing right now */
+ spin_lock_bh(&elm->lock);
+ elm327_send(elm, ELM327_DUMMY_STRING, 1);
+ spin_unlock_bh(&elm->lock);
+
+ netif_stop_queue(dev);
+
+ /* Give UART one final chance to flush. */
+ clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+ flush_work(&elm->tx_work);
+
+ can_rx_offload_disable(&elm->offload);
+ elm->can.state = CAN_STATE_STOPPED;
+ can_rx_offload_del(&elm->offload);
+ close_candev(dev);
+ can_led_event(dev, CAN_LED_EVENT_STOP);
+
+ return 0;
+}
+
+/* Send a can_frame to a TTY. */
+static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
+ struct net_device *dev)
+{
+ struct elmcan *elm = netdev_priv(dev);
+ struct can_frame *frame = (struct can_frame *)skb->data;
+
+ if (can_dropped_invalid_skb(dev, skb))
+ return NETDEV_TX_OK;
+
+ /* BHs are already disabled, so no spin_lock_bh().
+ * See Documentation/networking/netdevices.txt
+ */
+ spin_lock(&elm->lock);
+
+ /* We shouldn't get here after a hardware fault:
+ * can_bus_off() calls netif_carrier_off()
+ */
+ WARN_ON_ONCE(elm->uart_side_failure);
+
+ if (!elm->tty ||
+ elm->uart_side_failure ||
+ elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
+ spin_unlock(&elm->lock);
+ goto out;
+ }
+
+ netif_stop_queue(dev);
+
+ elm327_send_frame(elm, frame);
+ spin_unlock(&elm->lock);
+
+ dev->stats.tx_packets++;
+ dev->stats.tx_bytes += frame->len;
+
+ can_led_event(dev, CAN_LED_EVENT_TX);
+
+out:
+ kfree_skb(skb);
+ return NETDEV_TX_OK;
+}
+
+static const struct net_device_ops elmcan_netdev_ops = {
+ .ndo_open = elmcan_netdev_open,
+ .ndo_stop = elmcan_netdev_close,
+ .ndo_start_xmit = elmcan_netdev_start_xmit,
+ .ndo_change_mtu = can_change_mtu,
+};
+
+static bool elmcan_is_valid_rx_char(char c)
+{
+ return (isdigit(c) ||
+ isupper(c) ||
+ c == ELM327_DUMMY_CHAR ||
+ c == ELM327_READY_CHAR ||
+ c == '<' ||
+ c == 'a' ||
+ c == 'b' ||
+ c == 'v' ||
+ c == '.' ||
+ c == '?' ||
+ c == '\r' ||
+ c == ' ');
+}
+
+/* Handle incoming ELM327 ASCII data.
+ * This will not be re-entered while running, but other ldisc
+ * functions may be called in parallel.
+ */
+static void elmcan_ldisc_rx(struct tty_struct *tty,
+ const unsigned char *cp, const char *fp, int count)
+{
+ struct elmcan *elm = (struct elmcan *)tty->disc_data;
+
+ spin_lock_bh(&elm->lock);
+
+ if (elm->uart_side_failure)
+ goto out;
+
+ while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
+ if (fp && *fp++) {
+ netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
+
+ elm327_uart_side_failure(elm);
+
+ goto out;
+ }
+
+ /* Ignore NUL characters, which the PIC microcontroller may
+ * inadvertently insert due to a known hardware bug.
+ * See ELM327 documentation, which refers to a Microchip PIC
+ * bug description.
+ */
+ if (*cp != 0) {
+ /* Check for stray characters on the UART line.
+ * Likely caused by bad hardware.
+ */
+ if (!elmcan_is_valid_rx_char(*cp)) {
+ netdev_err(elm->dev,
+ "Received illegal character %02x.\n",
+ *cp);
+ elm327_uart_side_failure(elm);
+
+ goto out;
+ }
+
+ elm->rxbuf[elm->rxfill++] = *cp;
+ }
+
+ cp++;
+ }
+
+ if (count >= 0) {
+ netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
+
+ elm327_uart_side_failure(elm);
+
+ goto out;
+ }
+
+ elm327_parse_rxbuf(elm);
+
+out:
+ spin_unlock_bh(&elm->lock);
+}
+
+/* Write out remaining transmit buffer.
+ * Scheduled when TTY is writable.
+ */
+static void elmcan_ldisc_tx_worker(struct work_struct *work)
+{
+ struct elmcan *elm = container_of(work, struct elmcan, tx_work);
+ ssize_t written;
+
+ if (elm->uart_side_failure)
+ return;
+
+ spin_lock_bh(&elm->lock);
+
+ if (elm->txleft) {
+ written = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
+ if (written < 0) {
+ netdev_err(elm->dev,
+ "Failed to write to tty %s.\n",
+ elm->tty->name);
+ elm327_uart_side_failure(elm);
+ spin_unlock_bh(&elm->lock);
+ return;
+ } else {
+ elm->txleft -= written;
+ elm->txhead += written;
+ }
+ }
+
+ if (!elm->txleft) {
+ clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+ spin_unlock_bh(&elm->lock);
+ } else {
+ spin_unlock_bh(&elm->lock);
+ }
+}
+
+/* Called by the driver when there's room for more data. */
+static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
+{
+ struct elmcan *elm = (struct elmcan *)tty->disc_data;
+
+ schedule_work(&elm->tx_work);
+}
+
+/* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
+ * or 7/8 of that. Divisors are 1 to 64.
+ * Currently we don't implement support for 7/8 rates.
+ */
+static const u32 elmcan_bitrate_const[64] = {
+ 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
+ 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
+ 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
+ 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
+ 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
+ 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
+ 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
+ 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
+};
+
+/* Dummy needed to use bitrate_const */
+static int elmcan_do_set_bittiming(struct net_device *netdev)
+{
+ return 0;
+}
+
+static int elmcan_ldisc_open(struct tty_struct *tty)
+{
+ struct net_device *dev;
+ struct elmcan *elm;
+ int err;
+
+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
+
+ if (!tty->ops->write)
+ return -EOPNOTSUPP;
+
+ dev = alloc_candev(sizeof(struct elmcan), 0);
+ if (!dev)
+ return -ENFILE;
+ elm = netdev_priv(dev);
+
+ /* Configure TTY interface */
+ tty->receive_room = 65536; /* We don't flow control */
+ spin_lock_init(&elm->lock);
+ INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
+
+ /* Configure CAN metadata */
+ elm->can.bitrate_const = elmcan_bitrate_const;
+ elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
+ elm->can.do_set_bittiming = elmcan_do_set_bittiming;
+ elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
+
+ /* Configure netdev interface */
+ elm->dev = dev;
+ dev->netdev_ops = &elmcan_netdev_ops;
+
+ /* Mark ldisc channel as alive */
+ elm->tty = tty;
+ tty->disc_data = elm;
+
+ devm_can_led_init(elm->dev);
+
+ /* Let 'er rip */
+ err = register_candev(elm->dev);
+ if (err)
+ goto out_err;
+
+ netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
+
+ return 0;
+
+out_err:
+ free_candev(elm->dev);
+ return err;
+}
+
+/* Close down an elmcan channel.
+ * This means flushing out any pending queues, and then returning.
+ * This call is serialized against other ldisc functions:
+ * Once this is called, no other ldisc function of ours is entered.
+ *
+ * We also use this function for a hangup event.
+ */
+static void elmcan_ldisc_close(struct tty_struct *tty)
+{
+ struct elmcan *elm = (struct elmcan *)tty->disc_data;
+
+ /* unregister_netdev() calls .ndo_stop() so we don't have to.
+ * Our .ndo_stop() also flushes the TTY write wakeup handler,
+ * so we can safely set elm->tty = NULL after this.
+ */
+ unregister_candev(elm->dev);
+
+ /* Mark channel as dead */
+ spin_lock_bh(&elm->lock);
+ tty->disc_data = NULL;
+ elm->tty = NULL;
+ spin_unlock_bh(&elm->lock);
+
+ netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
+
+ free_candev(elm->dev);
+}
+
+static int elmcan_ldisc_ioctl(struct tty_struct *tty,
+ unsigned int cmd, unsigned long arg)
+{
+ struct elmcan *elm = (struct elmcan *)tty->disc_data;
+ unsigned int tmp;
+
+ switch (cmd) {
+ case SIOCGIFNAME:
+ tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
+ if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
+ return -EFAULT;
+ return 0;
+
+ case SIOCSIFHWADDR:
+ return -EINVAL;
+
+ default:
+ return tty_mode_ioctl(tty, cmd, arg);
+ }
+}
+
+static struct tty_ldisc_ops elmcan_ldisc = {
+ .owner = THIS_MODULE,
+ .name = "elmcan",
+ .num = N_ELMCAN,
+ .receive_buf = elmcan_ldisc_rx,
+ .write_wakeup = elmcan_ldisc_tx_wakeup,
+ .open = elmcan_ldisc_open,
+ .close = elmcan_ldisc_close,
+ .ioctl = elmcan_ldisc_ioctl,
+};
+
+static int __init elmcan_init(void)
+{
+ int status;
+
+ status = tty_register_ldisc(&elmcan_ldisc);
+ if (status)
+ pr_err("Can't register line discipline\n");
+
+ return status;
+}
+
+static void __exit elmcan_exit(void)
+{
+ /* This will only be called when all channels have been closed by
+ * userspace - tty_ldisc.c takes care of the module's refcount.
+ */
+ tty_unregister_ldisc(&elmcan_ldisc);
+}
+
+module_init(elmcan_init);
+module_exit(elmcan_exit);
+
+MODULE_ALIAS_LDISC(N_ELMCAN);
+MODULE_DESCRIPTION("ELM327 based CAN interface");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Max Staudt <max@enpas.org>");
diff --git a/include/uapi/linux/tty.h b/include/uapi/linux/tty.h
index 9d0f06bfbac3..bd034d0511f6 100644
--- a/include/uapi/linux/tty.h
+++ b/include/uapi/linux/tty.h
@@ -38,8 +38,9 @@
#define N_NULL 27 /* Null ldisc used for error handling */
#define N_MCTP 28 /* MCTP-over-serial */
#define N_DEVELOPMENT 29 /* Manual out-of-tree testing */
+#define N_ELMCAN 30 /* Serial / USB serial OBD-II Interfaces */

/* Always the newest line discipline + 1 */
-#define NR_LDISCS 30
+#define NR_LDISCS 31

#endif /* _UAPI_LINUX_TTY_H */
--
2.30.2
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