can: fix handling of unmodifiable configuration options

As described in 'can: m_can: tag current CAN FD controllers as non-ISO'
(6cfda7fbebe) it is possible to define fixed configuration options by
setting the according bit in 'ctrlmode' and clear it in 'ctrlmode_supported'.
This leads to the incovenience that the fixed configuration bits can not be
passed by netlink even when they have the correct values (e.g. non-ISO, FD).

This patch fixes that issue and not only allows fixed set bit values to be set
again but now requires(!) to provide these fixed values at configuration time.
A valid CAN FD configuration consists of a nominal/arbitration bittiming, a
data bittiming and a control mode with CAN_CTRLMODE_FD set - which is now
enforced by a new can_validate() function. This fix additionally removed the
inconsistency that was prohibiting the support of 'CANFD-only' controller
drivers, like the RCar CAN FD.

For this reason a new helper can_set_static_ctrlmode() has been introduced to
provide a proper interface to handle static enabled CAN controller options.

Reported-by: Ramesh Shanmugasundaram <ramesh.shanmugasundaram@bp.renesas.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Reviewed-by: Ramesh Shanmugasundaram  <ramesh.shanmugasundaram@bp.renesas.com>
Cc: <stable@vger.kernel.org> # >= 3.18
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 20 insertions, 2 deletions

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 735f9f8c4e43..5261751f6bd4 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -40,8 +40,11 @@ struct can_priv {
         struct can_clock clock;
 
         enum can_state state;
-        u32 ctrlmode;
-        u32 ctrlmode_supported;
+
+        /* CAN controller features - see include/uapi/linux/can/netlink.h */
+        u32 ctrlmode;           /* current options setting */
+        u32 ctrlmode_supported; /* options that can be modified by netlink */
+        u32 ctrlmode_static;    /* static enabled options for driver/hardware */
 
         int restart_ms;
         struct timer_list restart_timer;
@@ -108,6 +111,21 @@ static inline bool can_is_canfd_skb(const struct sk_buff *skb)
         return skb->len == CANFD_MTU;
 }
 
+/* helper to define static CAN controller features at device creation time */
+static inline void can_set_static_ctrlmode(struct net_device *dev,
+                                           u32 static_mode)
+{
+        struct can_priv *priv = netdev_priv(dev);
+
+        /* alloc_candev() succeeded => netdev_priv() is valid at this point */
+        priv->ctrlmode = static_mode;
+        priv->ctrlmode_static = static_mode;
+
+        /* override MTU which was set by default in can_setup()? */
+        if (static_mode & CAN_CTRLMODE_FD)
+                dev->mtu = CANFD_MTU;
+}
+
 /* get data length from can_dlc with sanitized can_dlc */
 u8 can_dlc2len(u8 can_dlc);