can: allow to change the device mtu for CAN FD capable devices

The configuration for CAN FD depends on CAN_CTRLMODE_FD enabled in the driver
specific ctrlmode_supported capabilities.

The configuration can be done either with the 'fd { on | off }' option in the
'ip' tool from iproute2 or by setting the CAN netdevice MTU to CAN_MTU (16) or
to CANFD_MTU (72).

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Acked-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

3 files changed, 41 insertions, 0 deletions

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 8ebe112458c4..4e20d82b799e 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -595,6 +595,39 @@ void free_candev(struct net_device *dev)
 EXPORT_SYMBOL_GPL(free_candev);
 
 /*
+ * changing MTU and control mode for CAN/CANFD devices
+ */
+int can_change_mtu(struct net_device *dev, int new_mtu)
+{
+        struct can_priv *priv = netdev_priv(dev);
+
+        /* Do not allow changing the MTU while running */
+        if (dev->flags & IFF_UP)
+                return -EBUSY;
+
+        /* allow change of MTU according to the CANFD ability of the device */
+        switch (new_mtu) {
+        case CAN_MTU:
+                priv->ctrlmode &= ~CAN_CTRLMODE_FD;
+                break;
+
+        case CANFD_MTU:
+                if (!(priv->ctrlmode_supported & CAN_CTRLMODE_FD))
+                        return -EINVAL;
+
+                priv->ctrlmode |= CAN_CTRLMODE_FD;
+                break;
+
+        default:
+                return -EINVAL;
+        }
+
+        dev->mtu = new_mtu;
+        return 0;
+}
+EXPORT_SYMBOL_GPL(can_change_mtu);
+
+/*
  * Common open function when the device gets opened.
  *
  * This function should be called in the open function of the device
@@ -693,6 +726,12 @@ static int can_changelink(struct net_device *dev,
                         return -EOPNOTSUPP;
                 priv->ctrlmode &= ~cm->mask;
                 priv->ctrlmode |= cm->flags;
+
+                /* 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;
         }
 
         if (data[IFLA_CAN_RESTART_MS]) {
diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 8adaee96f292..3ce5e526525f 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -113,6 +113,7 @@ struct can_priv *safe_candev_priv(struct net_device *dev);
 
 int open_candev(struct net_device *dev);
 void close_candev(struct net_device *dev);
+int can_change_mtu(struct net_device *dev, int new_mtu);
 
 int register_candev(struct net_device *dev);
 void unregister_candev(struct net_device *dev);
diff --git a/include/uapi/linux/can/netlink.h b/include/uapi/linux/can/netlink.h
index b41933d6bdcd..7e2e1863db16 100644
--- a/include/uapi/linux/can/netlink.h
+++ b/include/uapi/linux/can/netlink.h
@@ -96,6 +96,7 @@ struct can_ctrlmode {
 #define CAN_CTRLMODE_3_SAMPLES          0x04    /* Triple sampling mode */
 #define CAN_CTRLMODE_ONE_SHOT           0x08    /* One-Shot mode */
 #define CAN_CTRLMODE_BERR_REPORTING     0x10    /* Bus-error reporting */
+#define CAN_CTRLMODE_FD                 0x20    /* CAN FD mode */
 
 /*
  * CAN device statistics