can: populate the minimum and maximum MTU values

By populating:

  net_device->min_mtu

and

  net_device->max_mtu

the net core infrastructure will automatically:

  1. validate that the user's inputs are in range.

  2. report those min and max MTU values through the netlink
     interface.

Add can_set_default_mtu() which sets the default mtu value as well as
the minimum and maximum values. The logic for the default mtu value
remains unchanged:

  - CANFD_MTU if the device has a static CAN_CTRLMODE_FD.

  - CAN_MTU otherwise.

Call can_set_default_mtu() each time the CAN_CTRLMODE_FD is modified.
This will guarantee that the MTU value is always consistent with the
control mode flags.

With this, the checks done in can_change_mtu() become fully redundant
and will be removed in an upcoming change and it is now possible to
confirm the minimum and maximum MTU values on a physical CAN interface
by doing:

  $ ip --details link show can0

The virtual interfaces (vcan and vxcan) are not impacted by this
change.

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Link: https://patch.msgid.link/20250923-can-fix-mtu-v3-3-581bde113f52@kernel.org
[mkl: squashed https://patch.msgid.link/20250924143644.17622-2-mailhol@kernel.org]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/dev/dev.c b/drivers/net/can/dev/dev.c
index 02bfed37cc93d02eb8ccf587fdcb38d93667c1a3..befdeb4c54c299af4a227e2d151c4c2d57191bc6 100644 (file)
--- a/drivers/net/can/dev/dev.c
+++ b/drivers/net/can/dev/dev.c
@@ -240,6 +240,8 @@ void can_setup(struct net_device *dev)
 {
        dev->type = ARPHRD_CAN;
        dev->mtu = CAN_MTU;
+       dev->min_mtu = CAN_MTU;
+       dev->max_mtu = CAN_MTU;
        dev->hard_header_len = 0;
        dev->addr_len = 0;
        dev->tx_queue_len = 10;
@@ -309,6 +311,21 @@ void free_candev(struct net_device *dev)
 }
 EXPORT_SYMBOL_GPL(free_candev);
 
+void can_set_default_mtu(struct net_device *dev)
+{
+       struct can_priv *priv = netdev_priv(dev);
+
+       if (priv->ctrlmode & CAN_CTRLMODE_FD) {
+               dev->mtu = CANFD_MTU;
+               dev->min_mtu = CANFD_MTU;
+               dev->max_mtu = CANFD_MTU;
+       } else {
+               dev->mtu = CAN_MTU;
+               dev->min_mtu = CAN_MTU;
+               dev->max_mtu = CAN_MTU;
+       }
+}
+
 /* changing MTU and control mode for CAN/CANFD devices */
 int can_change_mtu(struct net_device *dev, int new_mtu)
 {
@@ -361,8 +378,7 @@ int can_set_static_ctrlmode(struct net_device *dev, u32 static_mode)
        priv->ctrlmode = static_mode;
 
        /* override MTU which was set by default in can_setup()? */
-       if (static_mode & CAN_CTRLMODE_FD)
-               dev->mtu = CANFD_MTU;
+       can_set_default_mtu(dev);
 
        return 0;
 }

diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
index d9f6ab3efb9767409c318b714f19df8a30e51137..248f607e3864ffbda6f0b8daf4e2484179cf9cd5 100644 (file)
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -223,17 +223,16 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
                priv->ctrlmode &= ~cm->mask;
                priv->ctrlmode |= maskedflags;
 
-               /* CAN_CTRLMODE_FD can only be set when driver supports FD */
-               if (priv->ctrlmode & CAN_CTRLMODE_FD) {
-                       dev->mtu = CANFD_MTU;
-               } else {
-                       dev->mtu = CAN_MTU;
+               /* Wipe potential leftovers from previous CAN FD config */
+               if (!(priv->ctrlmode & CAN_CTRLMODE_FD)) {
                        memset(&priv->fd.data_bittiming, 0,
                               sizeof(priv->fd.data_bittiming));
                        priv->ctrlmode &= ~CAN_CTRLMODE_FD_TDC_MASK;
                        memset(&priv->fd.tdc, 0, sizeof(priv->fd.tdc));
                }
 
+               can_set_default_mtu(dev);
+
                fd_tdc_flag_provided = cm->mask & CAN_CTRLMODE_FD_TDC_MASK;
                /* CAN_CTRLMODE_TDC_{AUTO,MANUAL} are mutually
                 * exclusive: make sure to turn the other one off

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 5dc58360c2d74a1711d4e02d28fe52ae20b146e0..3354f70ed2c684d7d482549560d4cb5838cbebd5 100644 (file)
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -166,6 +166,7 @@ struct can_priv *safe_candev_priv(struct net_device *dev);
 
 int open_candev(struct net_device *dev);
 void close_candev(struct net_device *dev);
+void can_set_default_mtu(struct net_device *dev);
 int can_change_mtu(struct net_device *dev, int new_mtu);
 int __must_check can_set_static_ctrlmode(struct net_device *dev,
                                         u32 static_mode);