can: slcan: use CAN network device driver API

As suggested by commit [1], now the driver uses the functions and the
data structures provided by the CAN network device driver interface.

Currently the driver doesn't implement a way to set bitrate for SLCAN
based devices via ip tool, so you'll have to do this by slcand or
slcan_attach invocation through the -sX parameter:

- slcan_attach -f -s6 -o /dev/ttyACM0
- slcand -f -s8 -o /dev/ttyUSB0

where -s6 in will set adapter's bitrate to 500 Kbit/s and -s8 to
1Mbit/s.
See the table below for further CAN bitrates:
- s0 ->   10 Kbit/s
- s1 ->   20 Kbit/s
- s2 ->   50 Kbit/s
- s3 ->  100 Kbit/s
- s4 ->  125 Kbit/s
- s5 ->  250 Kbit/s
- s6 ->  500 Kbit/s
- s7 ->  800 Kbit/s
- s8 -> 1000 Kbit/s

In doing so, the struct can_priv::bittiming.bitrate of the driver is not
set and since the open_candev() checks that the bitrate has been set, it
must be a non-zero value, the bitrate is set to a fake value (-1U)
before it is called.

Using the rtnl_lock()/rtnl_unlock() functions has become a bit more
tricky as the register_candev() function indirectly calls rtnl_lock()
via register_netdev(). To avoid a deadlock it is therefore necessary to
call rtnl_unlock() before calling register_candev(). The same goes for
the unregister_candev() function.

[1] commit 39549eef3587f ("can: CAN Network device driver and Netlink interface")

Link: https://lore.kernel.org/all/20220628163137.413025-6-dario.binacchi@amarulasolutions.com
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Tested-by: Jeroen Hofstee <jhofstee@victronenergy.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 20 insertions, 20 deletions

diff --git a/drivers/net/can/Kconfig b/drivers/net/can/Kconfig
index 4078d0775572..3048ad77edb3 100644
--- a/drivers/net/can/Kconfig
+++ b/drivers/net/can/Kconfig
@@ -49,26 +49,6 @@ config CAN_VXCAN
 	  This driver can also be built as a module.  If so, the module
 	  will be called vxcan.
 
-config CAN_SLCAN
-	tristate "Serial / USB serial CAN Adaptors (slcan)"
-	depends on TTY
-	help
-	  CAN driver for several 'low cost' CAN interfaces that are attached
-	  via serial lines or via USB-to-serial adapters using the LAWICEL
-	  ASCII protocol. The driver implements the tty linediscipline N_SLCAN.
-
-	  As only the sending and receiving of CAN frames is implemented, this
-	  driver should work with the (serial/USB) CAN hardware from:
-	  www.canusb.com / www.can232.com / www.mictronics.de / www.canhack.de
-
-	  Userspace tools to attach the SLCAN line discipline (slcan_attach,
-	  slcand) can be found in the can-utils at the linux-can project, see
-	  https://github.com/linux-can/can-utils for details.
-
-	  The slcan driver supports up to 10 CAN netdevices by default which
-	  can be changed by the 'maxdev=xx' module option. This driver can
-	  also be built as a module. If so, the module will be called slcan.
-
 config CAN_NETLINK
 	bool "CAN device drivers with Netlink support"
 	default y
@@ -172,6 +152,26 @@ config CAN_KVASER_PCIEFD
 	    Kvaser Mini PCI Express HS v2
 	    Kvaser Mini PCI Express 2xHS v2
 
+config CAN_SLCAN
+	tristate "Serial / USB serial CAN Adaptors (slcan)"
+	depends on TTY
+	help
+	  CAN driver for several 'low cost' CAN interfaces that are attached
+	  via serial lines or via USB-to-serial adapters using the LAWICEL
+	  ASCII protocol. The driver implements the tty linediscipline N_SLCAN.
+
+	  As only the sending and receiving of CAN frames is implemented, this
+	  driver should work with the (serial/USB) CAN hardware from:
+	  www.canusb.com / www.can232.com / www.mictronics.de / www.canhack.de
+
+	  Userspace tools to attach the SLCAN line discipline (slcan_attach,
+	  slcand) can be found in the can-utils at the linux-can project, see
+	  https://github.com/linux-can/can-utils for details.
+
+	  The slcan driver supports up to 10 CAN netdevices by default which
+	  can be changed by the 'maxdev=xx' module option. This driver can
+	  also be built as a module. If so, the module will be called slcan.
+
 config CAN_SUN4I
 	tristate "Allwinner A10 CAN controller"
 	depends on MACH_SUN4I || MACH_SUN7I || COMPILE_TEST