[canxl v3 14/17] can: add dummy_can driver

Oliver Hartkopp
2025-11-20T18:45:39Z

During the development of CAN XL, we found the need of creating a
dummy CAN XL driver in order to test the new netlink interface. While
this code was initially intended to be some throwaway, it received
some positive feedback.

Add the dummy_can driver. This driver acts similarly to the vcan
interface in the sense that it will echo back any packet it receives.
The difference is that it exposes a set on bittiming parameters as a
real device would and thus must be configured as if it was a real
physical interface.

The driver comes with a debug mode. If debug message are enabled (for
example by enabling CONFIG_CAN_DEBUG_DEVICES), it will print in the
kernel log all the bittiming values, similar to what a:

ip --details link show can0

would do.

This driver is mostly intended for debugging and testing, but some
developers also may want to look at it as a simple reference
implementation.

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
drivers/net/can/Kconfig | 17 +++
drivers/net/can/Makefile | 1 +
drivers/net/can/dummy_can.c | 284 ++++++++++++++++++++++++++++++++++++
3 files changed, 302 insertions(+)
create mode 100644 drivers/net/can/dummy_can.c

diff --git a/drivers/net/can/Kconfig b/drivers/net/can/Kconfig
index d43d56694667..e15e320db476 100644
--- a/drivers/net/can/Kconfig
+++ b/drivers/net/can/Kconfig
@@ -122,10 +122,27 @@ config CAN_CAN327
Please refer to the documentation for information on how to use it:
Documentation/networking/device_drivers/can/can327.rst

If this driver is built as a module, it will be called can327.

+config CAN_DUMMY
+ tristate "Dummy CAN"
+ help
+ A dummy CAN module supporting Classical CAN, CAN FD and CAN XL. It
+ exposes bittiming values which can be configured through the netlink
+ interface.
+
+ The module will simply echo any frame sent to it. If debug messages
+ are activated, it prints all the CAN bittiming information in the
+ kernel log. Aside from that it does nothing.
+
+ This is convenient for testing the CAN netlink interface. Most of the
+ users will never need this. If unsure, say NO.
+
+ To compile this driver as a module, choose M here: the module will be
+ called dummy-can.
+
config CAN_FLEXCAN
tristate "Support for Freescale FLEXCAN based chips"
depends on OF || COLDFIRE || COMPILE_TEST
depends on HAS_IOMEM
select CAN_RX_OFFLOAD
diff --git a/drivers/net/can/Makefile b/drivers/net/can/Makefile
index 56138d8ddfd2..d7bc10a6b8ea 100644
--- a/drivers/net/can/Makefile
+++ b/drivers/net/can/Makefile
@@ -19,10 +19,11 @@ obj-$(CONFIG_CAN_AT91) += at91_can.o
obj-$(CONFIG_CAN_BXCAN) += bxcan.o
obj-$(CONFIG_CAN_CAN327) += can327.o
obj-$(CONFIG_CAN_CC770) += cc770/
obj-$(CONFIG_CAN_C_CAN) += c_can/
obj-$(CONFIG_CAN_CTUCANFD) += ctucanfd/
+obj-$(CONFIG_CAN_DUMMY) += dummy_can.o
obj-$(CONFIG_CAN_FLEXCAN) += flexcan/
obj-$(CONFIG_CAN_GRCAN) += grcan.o
obj-$(CONFIG_CAN_IFI_CANFD) += ifi_canfd/
obj-$(CONFIG_CAN_JANZ_ICAN3) += janz-ican3.o
obj-$(CONFIG_CAN_KVASER_PCIEFD) += kvaser_pciefd/
diff --git a/drivers/net/can/dummy_can.c b/drivers/net/can/dummy_can.c
new file mode 100644
index 000000000000..97af0847db00
--- /dev/null
+++ b/drivers/net/can/dummy_can.c
@@ -0,0 +1,284 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* Copyright (c) 2025 Vincent Mailhol <mailhol@kernel.org> */
+
+#include <linux/array_size.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/units.h>
+
+#include <linux/can.h>
+#include <linux/can/bittiming.h>
+#include <linux/can/dev.h>
+#include <linux/can/skb.h>
+
+struct dummy_can {
+ struct can_priv can;
+ struct net_device *dev;
+};
+
+static struct dummy_can *dummy_can;
+
+static const struct can_bittiming_const dummy_can_bittiming_const = {
+ .name = "dummy_can CC",
+ .tseg1_min = 2,
+ .tseg1_max = 256,
+ .tseg2_min = 2,
+ .tseg2_max = 128,
+ .sjw_max = 128,
+ .brp_min = 1,
+ .brp_max = 512,
+ .brp_inc = 1
+};
+
+static const struct can_bittiming_const dummy_can_fd_databittiming_const = {
+ .name = "dummy_can FD",
+ .tseg1_min = 2,
+ .tseg1_max = 256,
+ .tseg2_min = 2,
+ .tseg2_max = 128,
+ .sjw_max = 128,
+ .brp_min = 1,
+ .brp_max = 512,
+ .brp_inc = 1
+};
+
+static const struct can_tdc_const dummy_can_fd_tdc_const = {
+ .tdcv_min = 0,
+ .tdcv_max = 0, /* Manual mode not supported. */
+ .tdco_min = 0,
+ .tdco_max = 127,
+ .tdcf_min = 0,
+ .tdcf_max = 127
+};
+
+static const struct can_bittiming_const dummy_can_xl_databittiming_const = {
+ .name = "dummy_can XL",
+ .tseg1_min = 2,
+ .tseg1_max = 256,
+ .tseg2_min = 2,
+ .tseg2_max = 128,
+ .sjw_max = 128,
+ .brp_min = 1,
+ .brp_max = 512,
+ .brp_inc = 1
+};
+
+static const struct can_tdc_const dummy_can_xl_tdc_const = {
+ .tdcv_min = 0,
+ .tdcv_max = 0, /* Manual mode not supported. */
+ .tdco_min = 0,
+ .tdco_max = 127,
+ .tdcf_min = 0,
+ .tdcf_max = 127
+};
+
+static const struct can_pwm_const dummy_can_pwm_const = {
+ .pwms_min = 1,
+ .pwms_max = 8,
+ .pwml_min = 2,
+ .pwml_max = 24,
+ .pwmo_min = 0,
+ .pwmo_max = 16,
+};
+
+static void dummy_can_print_bittiming(struct net_device *dev,
+ struct can_bittiming *bt)
+{
+ netdev_dbg(dev, "\tbitrate: %u\n", bt->bitrate);
+ netdev_dbg(dev, "\tsample_point: %u\n", bt->sample_point);
+ netdev_dbg(dev, "\ttq: %u\n", bt->tq);
+ netdev_dbg(dev, "\tprop_seg: %u\n", bt->prop_seg);
+ netdev_dbg(dev, "\tphase_seg1: %u\n", bt->phase_seg1);
+ netdev_dbg(dev, "\tphase_seg2: %u\n", bt->phase_seg2);
+ netdev_dbg(dev, "\tsjw: %u\n", bt->sjw);
+ netdev_dbg(dev, "\tbrp: %u\n", bt->brp);
+}
+
+static void dummy_can_print_tdc(struct net_device *dev, struct can_tdc *tdc)
+{
+ netdev_dbg(dev, "\t\ttdcv: %u\n", tdc->tdcv);
+ netdev_dbg(dev, "\t\ttdco: %u\n", tdc->tdco);
+ netdev_dbg(dev, "\t\ttdcf: %u\n", tdc->tdcf);
+}
+
+static void dummy_can_print_pwm(struct net_device *dev, struct can_pwm *pwm,
+ struct can_bittiming *dbt)
+{
+ netdev_dbg(dev, "\t\tpwms: %u\n", pwm->pwms);
+ netdev_dbg(dev, "\t\tpwml: %u\n", pwm->pwml);
+ netdev_dbg(dev, "\t\tpwmo: %u\n", pwm->pwmo);
+}
+
+static void dummy_can_print_ctrlmode(struct net_device *dev)
+{
+ struct dummy_can *priv = netdev_priv(dev);
+ struct can_priv *can_priv = &priv->can;
+ unsigned long supported = can_priv->ctrlmode_supported;
+ u32 enabled = can_priv->ctrlmode;
+
+ netdev_dbg(dev, "Control modes:\n");
+ netdev_dbg(dev, "\tsupported: 0x%08x\n", (u32)supported);
+ netdev_dbg(dev, "\tenabled: 0x%08x\n", enabled);
+
+ if (supported) {
+ int idx;
+
+ netdev_dbg(dev, "\tlist:");
+ for_each_set_bit(idx, &supported, BITS_PER_TYPE(u32))
+ netdev_dbg(dev, "\t\t%s: %s\n",
+ can_get_ctrlmode_str(BIT(idx)),
+ enabled & BIT(idx) ? "on" : "off");
+ }
+}
+
+static void dummy_can_print_bittiming_info(struct net_device *dev)
+{
+ struct dummy_can *priv = netdev_priv(dev);
+ struct can_priv *can_priv = &priv->can;
+
+ netdev_dbg(dev, "Clock frequency: %u\n", can_priv->clock.freq);
+ netdev_dbg(dev, "Maximum bitrate: %u\n", can_priv->bitrate_max);
+ netdev_dbg(dev, "MTU: %u\n", dev->mtu);
+ netdev_dbg(dev, "\n");
+
+ dummy_can_print_ctrlmode(dev);
+ netdev_dbg(dev, "\n");
+
+ netdev_dbg(dev, "Classical CAN nominal bittiming:\n");
+ dummy_can_print_bittiming(dev, &can_priv->bittiming);
+ netdev_dbg(dev, "\n");
+
+ if (can_priv->ctrlmode & CAN_CTRLMODE_FD) {
+ netdev_dbg(dev, "CAN FD databittiming:\n");
+ dummy_can_print_bittiming(dev, &can_priv->fd.data_bittiming);
+ if (can_fd_tdc_is_enabled(can_priv)) {
+ netdev_dbg(dev, "\tCAN FD TDC:\n");
+ dummy_can_print_tdc(dev, &can_priv->fd.tdc);
+ }
+ }
+ netdev_dbg(dev, "\n");
+
+ if (can_priv->ctrlmode & CAN_CTRLMODE_XL) {
+ netdev_dbg(dev, "CAN XL databittiming:\n");
+ dummy_can_print_bittiming(dev, &can_priv->xl.data_bittiming);
+ if (can_xl_tdc_is_enabled(can_priv)) {
+ netdev_dbg(dev, "\tCAN XL TDC:\n");
+ dummy_can_print_tdc(dev, &can_priv->xl.tdc);
+ }
+ if (can_priv->ctrlmode & CAN_CTRLMODE_XL_TMS) {
+ netdev_dbg(dev, "\tCAN XL PWM:\n");
+ dummy_can_print_pwm(dev, &can_priv->xl.pwm,
+ &can_priv->xl.data_bittiming);
+ }
+ }
+ netdev_dbg(dev, "\n");
+}
+
+static int dummy_can_netdev_open(struct net_device *dev)
+{
+ int ret;
+ struct can_priv *priv = netdev_priv(dev);
+
+ dummy_can_print_bittiming_info(dev);
+ netdev_dbg(dev, "error-signalling is %sabled\n",
+ can_dev_in_xl_only_mode(priv)?"dis":"en");
+
+ ret = open_candev(dev);
+ if (ret)
+ return ret;
+ netif_start_queue(dev);
+ netdev_dbg(dev, "dummy-can is up\n");
+
+ return 0;
+}
+
+static int dummy_can_netdev_close(struct net_device *dev)
+{
+ netif_stop_queue(dev);
+ close_candev(dev);
+ netdev_dbg(dev, "dummy-can is down\n");
+
+ return 0;
+}
+
+static netdev_tx_t dummy_can_start_xmit(struct sk_buff *skb,
+ struct net_device *dev)
+{
+ if (can_dev_dropped_skb(dev, skb))
+ return NETDEV_TX_OK;
+
+ can_put_echo_skb(skb, dev, 0, 0);
+ dev->stats.tx_packets++;
+ dev->stats.tx_bytes += can_get_echo_skb(dev, 0, NULL);
+
+ return NETDEV_TX_OK;
+}
+
+static const struct net_device_ops dummy_can_netdev_ops = {
+ .ndo_open = dummy_can_netdev_open,
+ .ndo_stop = dummy_can_netdev_close,
+ .ndo_start_xmit = dummy_can_start_xmit,
+};
+
+static const struct ethtool_ops dummy_can_ethtool_ops = {
+ .get_ts_info = ethtool_op_get_ts_info,
+};
+
+static int __init dummy_can_init(void)
+{
+ struct net_device *dev;
+ struct dummy_can *priv;
+ int ret;
+
+ dev = alloc_candev(sizeof(*priv), 1);
+ if (!dev)
+ return -ENOMEM;
+
+ dev->netdev_ops = &dummy_can_netdev_ops;
+ dev->ethtool_ops = &dummy_can_ethtool_ops;
+ priv = netdev_priv(dev);
+ priv->can.bittiming_const = &dummy_can_bittiming_const;
+ priv->can.bitrate_max = 20 * MEGA /* BPS */;
+ priv->can.clock.freq = 160 * MEGA /* Hz */;
+ priv->can.fd.data_bittiming_const = &dummy_can_fd_databittiming_const;
+ priv->can.fd.tdc_const = &dummy_can_fd_tdc_const;
+ priv->can.xl.data_bittiming_const = &dummy_can_xl_databittiming_const;
+ priv->can.xl.tdc_const = &dummy_can_xl_tdc_const;
+ priv->can.xl.pwm_const = &dummy_can_pwm_const;
+ priv->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
+ CAN_CTRLMODE_FD | CAN_CTRLMODE_TDC_AUTO |
+ CAN_CTRLMODE_RESTRICTED | CAN_CTRLMODE_XL |
+ CAN_CTRLMODE_XL_TDC_AUTO | CAN_CTRLMODE_XL_TMS;
+ priv->dev = dev;
+
+ ret = register_candev(priv->dev);
+ if (ret) {
+ free_candev(priv->dev);
+ return ret;
+ }
+
+ dummy_can = priv;
+ netdev_dbg(dev, "dummy-can ready\n");
+
+ return 0;
+}
+
+static void __exit dummy_can_exit(void)
+{
+ struct net_device *dev = dummy_can->dev;
+
+ netdev_dbg(dev, "dummy-can bye bye\n");
+ unregister_candev(dev);
+ free_candev(dev);
+}
+
+module_init(dummy_can_init);
+module_exit(dummy_can_exit);
+
+MODULE_DESCRIPTION("A dummy CAN driver, mainly to test the netlink interface");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Vincent Mailhol <mailhol@kernel.org>");
--
2.47.3