[canxl v3 06/17] can: dev: can_dev_dropped_skb: drop CC/FD frames in CANXL-only mode

Oliver Hartkopp
2025-11-20T18:45:29Z

The error-signalling (ES) is a mandatory functionality for CAN CC and
CAN FD to report CAN frame format violations by sending an error-frame
signal on the bus.

A so-called 'mixed-mode' is intended to have (XL-tolerant) CAN FD nodes
and CAN XL nodes on one CAN segment, where the FD-controllers can talk
CC/FD and the XL-controllers can talk CC/FD/XL. This mixed-mode
utilizes the error-signalling for sending CC/FD/XL frames.

The CANXL-only mode disables the error-signalling in the CAN XL
controller. This mode does not allow CC/FD frames to be sent but
additionally offers a CAN XL transceiver mode switching (TMS).

Configured with CAN_CTRLMODE_FD and CAN_CTRLMODE_XL this leads to:

FD=0 XL=0 CC-only mode (ES=1)
FD=1 XL=0 FD/CC mixed-mode (ES=1)
FD=1 XL=1 XL/FD/CC mixed-mode (ES=1)
FD=0 XL=1 XL-only mode (ES=0, TMS optional)

The helper function can_dev_in_xl_only_mode() determines the required
value to disable error signalling in the CAN XL controller.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
include/linux/can/dev.h | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 945c16743702..13b25b0dceeb 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -129,10 +129,23 @@ int can_restart_now(struct net_device *dev);
void can_bus_off(struct net_device *dev);

const char *can_get_state_str(const enum can_state state);
const char *can_get_ctrlmode_str(u32 ctrlmode);

+static inline bool can_dev_in_xl_only_mode(struct can_priv *priv)
+{
+ const u32 mixed_mode = CAN_CTRLMODE_FD | CAN_CTRLMODE_XL;
+
+ /* When CAN XL is enabled but FD is disabled we are running in
+ * the so-called 'CANXL-only mode' where the error signalling is
+ * disabled. This helper function determines the required value
+ * to disable error signalling in the CAN XL controller.
+ * The so-called CC/FD/XL 'mixed mode' requires error signalling.
+ */
+ return ((priv->ctrlmode & mixed_mode) == CAN_CTRLMODE_XL);
+}
+
/* drop skb if it does not contain a valid CAN frame for sending */
static inline bool can_dev_dropped_skb(struct net_device *dev, struct sk_buff *skb)
{
struct can_priv *priv = netdev_priv(dev);
u32 silent_mode = priv->ctrlmode & (CAN_CTRLMODE_LISTENONLY |
@@ -147,10 +160,16 @@ static inline bool can_dev_dropped_skb(struct net_device *dev, struct sk_buff *s
if (!(priv->ctrlmode & CAN_CTRLMODE_FD) && can_is_canfd_skb(skb)) {
netdev_info_once(dev, "CAN FD is disabled, dropping skb\n");
goto invalid_skb;
}

+ if (can_dev_in_xl_only_mode(priv) && !can_is_canxl_skb(skb)) {
+ netdev_info_once(dev,
+ "Error signaling is disabled, dropping skb\n");
+ goto invalid_skb;
+ }
+
return can_dropped_invalid_skb(dev, skb);

invalid_skb:
kfree_skb(skb);
dev->stats.tx_dropped++;
--
2.47.3