can: dev: add sanity check in can_set_static_ctrlmode()

Previous patch removed can_priv::ctrlmode_static to replace it with
can_get_static_ctrlmode().

A condition sine qua non for this to work is that the controller
static modes should never be set in can_priv::ctrlmode_supported
(c.f. the comment on can_priv::ctrlmode_supported which states that it
is for "options that can be *modified* by netlink"). Also, this
condition is already correctly fulfilled by all existing drivers
which rely on the ctrlmode_static feature.

Nonetheless, we added an extra safeguard in can_set_static_ctrlmode()
to return an error value and to warn the developer who would be
adventurous enough to set to static a given feature that is already
set to supported.

The drivers which rely on the static controller mode are then updated
to check the return value of can_set_static_ctrlmode().

Link: https://lore.kernel.org/all/[email protected]
Signed-off-by: Vincent Mailhol <[email protected]>
Signed-off-by: Marc Kleine-Budde <[email protected]>

drivers/net/can/m_can/m_can.c

@@ -1456,7 +1456,7 @@ static bool m_can_niso_supported(struct m_can_classdev *cdev)
 static int m_can_dev_setup(struct m_can_classdev *cdev)
 {
 	struct net_device *dev = cdev->net;
-	int m_can_version;
+	int m_can_version, err;
 
 	m_can_version = m_can_check_core_release(cdev);
 	/* return if unsupported version */
@@ -1486,7 +1486,9 @@ static int m_can_dev_setup(struct m_can_classdev *cdev)
 	switch (cdev->version) {
 	case 30:
 		/* CAN_CTRLMODE_FD_NON_ISO is fixed with M_CAN IP v3.0.x */
-		can_set_static_ctrlmode(dev, CAN_CTRLMODE_FD_NON_ISO);
+		err = can_set_static_ctrlmode(dev, CAN_CTRLMODE_FD_NON_ISO);
+		if (err)
+			return err;
 		cdev->can.bittiming_const = cdev->bit_timing ?
 			cdev->bit_timing : &m_can_bittiming_const_30X;
 
@@ -1496,7 +1498,9 @@ static int m_can_dev_setup(struct m_can_classdev *cdev)
 		break;
 	case 31:
 		/* CAN_CTRLMODE_FD_NON_ISO is fixed with M_CAN IP v3.1.x */
-		can_set_static_ctrlmode(dev, CAN_CTRLMODE_FD_NON_ISO);
+		err = can_set_static_ctrlmode(dev, CAN_CTRLMODE_FD_NON_ISO);
+		if (err)
+			return err;
 		cdev->can.bittiming_const = cdev->bit_timing ?
 			cdev->bit_timing : &m_can_bittiming_const_31X;
 

drivers/net/can/rcar/rcar_canfd.c

@@ -1699,7 +1699,9 @@ static int rcar_canfd_channel_probe(struct rcar_canfd_global *gpriv, u32 ch,
 			&rcar_canfd_data_bittiming_const;
 
 		/* Controller starts in CAN FD only mode */
-		can_set_static_ctrlmode(ndev, CAN_CTRLMODE_FD);
+		err = can_set_static_ctrlmode(ndev, CAN_CTRLMODE_FD);
+		if (err)
+			goto fail;
 		priv->can.ctrlmode_supported = CAN_CTRLMODE_BERR_REPORTING;
 	} else {
 		/* Controller starts in Classical CAN only mode */

include/linux/can/dev.h

@@ -131,17 +131,24 @@ static inline s32 can_get_relative_tdco(const struct can_priv *priv)
 }
 
 /* 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)
+static inline int __must_check 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 */
+	if (priv->ctrlmode_supported & static_mode) {
+		netdev_warn(dev,
+			    "Controller features can not be supported and static at the same time\n");
+		return -EINVAL;
+	}
 	priv->ctrlmode = static_mode;
 
 	/* override MTU which was set by default in can_setup()? */
 	if (static_mode & CAN_CTRLMODE_FD)
 		dev->mtu = CANFD_MTU;
+
+	return 0;
 }
 
 static inline u32 can_get_static_ctrlmode(struct can_priv *priv)