[RFC PATCH 04/13] can: slcan: use CAN network device driver API

[Dario Binacchi <dario.binacchi@amarulasolutions.com>]

As suggested by commit [1], now the driver uses the functions and the
data structures provided by the CAN network device driver interface.

There is no way to set bitrate for SLCAN based devices via ip tool, so
you'll have to do this by slcand/slcan_attach invocation through the
-sX parameter:

- slcan_attach -f -s6 -o /dev/ttyACM0
- slcand -f -s8 -o /dev/ttyUSB0

where -s6 in will set adapter's bitrate to 500 Kbit/s and -s8 to
1Mbit/s.
See the table below for further CAN bitrates:
- s0 ->   10 Kbit/s
- s1 ->   20 Kbit/s
- s2 ->   50 Kbit/s
- s3 ->  100 Kbit/s
- s4 ->  125 Kbit/s
- s5 ->  250 Kbit/s
- s6 ->  500 Kbit/s
- s7 ->  800 Kbit/s
- s8 -> 1000 Kbit/s

In doing so, the struct can_priv::bittiming.bitrate of the driver is not
set and since the open_candev() checks that the bitrate has been set, it
must be a non-zero value, the bitrate is set to a fake value (-1) before
it is called.

[1] 39549eef3587f ("can: CAN Network device driver and Netlink interface")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
---

 drivers/net/can/slcan.c | 112 ++++++++++++++++++++--------------------
 1 file changed, 57 insertions(+), 55 deletions(-)

diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
index 964b02f321ab..956b47bd40a7 100644
--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -56,7 +56,6 @@
 #include <linux/can.h>
 #include <linux/can/dev.h>
 #include <linux/can/skb.h>
-#include <linux/can/can-ml.h>
 
 MODULE_ALIAS_LDISC(N_SLCAN);
 MODULE_DESCRIPTION("serial line CAN interface");
@@ -79,6 +78,7 @@ MODULE_PARM_DESC(maxdev, "Maximum number of slcan interfaces");
 #define SLC_EFF_ID_LEN 8
 
 struct slcan {
+	struct can_priv         can;
 	int			magic;
 
 	/* Various fields. */
@@ -100,6 +100,7 @@ struct slcan {
 };
 
 static struct net_device **slcan_devs;
+static DEFINE_SPINLOCK(slcan_lock);
 
  /************************************************************************
   *			SLCAN ENCAPSULATION FORMAT			 *
@@ -369,7 +370,7 @@ static netdev_tx_t slc_xmit(struct sk_buff *skb, struct net_device *dev)
 	spin_unlock(&sl->lock);
 
 out:
-	kfree_skb(skb);
+	can_put_echo_skb(skb, dev, 0, 0);
 	return NETDEV_TX_OK;
 }
 
@@ -389,6 +390,8 @@ static int slc_close(struct net_device *dev)
 		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
 	}
 	netif_stop_queue(dev);
+	close_candev(dev);
+	sl->can.state = CAN_STATE_STOPPED;
 	sl->rcount   = 0;
 	sl->xleft    = 0;
 	spin_unlock_bh(&sl->lock);
@@ -400,21 +403,36 @@ static int slc_close(struct net_device *dev)
 static int slc_open(struct net_device *dev)
 {
 	struct slcan *sl = netdev_priv(dev);
+	int err;
 
 	if (sl->tty == NULL)
 		return -ENODEV;
 
+	/* The baud rate is not set with the command
+	 * `ip link set <iface> type can bitrate <baud>' and therefore
+	 * can.bittiming.bitrate is 0, causing open_candev() to fail.
+	 * So let's set to a fake value.
+	 */
+	sl->can.bittiming.bitrate = -1;
+	err = open_candev(dev);
+	if (err) {
+		netdev_err(dev, "failed to open can device\n");
+		return err;
+	}
+
+	sl->can.state = CAN_STATE_ERROR_ACTIVE;
 	sl->flags &= BIT(SLF_INUSE);
 	netif_start_queue(dev);
 	return 0;
 }
 
-/* Hook the destructor so we can free slcan devs at the right point in time */
-static void slc_free_netdev(struct net_device *dev)
+static void slc_dealloc(struct slcan *sl)
 {
-	int i = dev->base_addr;
+	int i = sl->dev->base_addr;
 
-	slcan_devs[i] = NULL;
+	free_candev(sl->dev);
+	if (slcan_devs)
+		slcan_devs[i] = NULL;
 }
 
 static int slcan_change_mtu(struct net_device *dev, int new_mtu)
@@ -429,24 +447,6 @@ static const struct net_device_ops slc_netdev_ops = {
 	.ndo_change_mtu         = slcan_change_mtu,
 };
 
-static void slc_setup(struct net_device *dev)
-{
-	dev->netdev_ops		= &slc_netdev_ops;
-	dev->needs_free_netdev	= true;
-	dev->priv_destructor	= slc_free_netdev;
-
-	dev->hard_header_len	= 0;
-	dev->addr_len		= 0;
-	dev->tx_queue_len	= 10;
-
-	dev->mtu		= CAN_MTU;
-	dev->type		= ARPHRD_CAN;
-
-	/* New-style flags. */
-	dev->flags		= IFF_NOARP;
-	dev->features           = NETIF_F_HW_CSUM;
-}
-
 /******************************************
   Routines looking at TTY side.
  ******************************************/
@@ -509,11 +509,8 @@ static void slc_sync(void)
 static struct slcan *slc_alloc(void)
 {
 	int i;
-	char name[IFNAMSIZ];
 	struct net_device *dev = NULL;
-	struct can_ml_priv *can_ml;
 	struct slcan       *sl;
-	int size;
 
 	for (i = 0; i < maxdev; i++) {
 		dev = slcan_devs[i];
@@ -526,16 +523,14 @@ static struct slcan *slc_alloc(void)
 	if (i >= maxdev)
 		return NULL;
 
-	sprintf(name, "slcan%d", i);
-	size = ALIGN(sizeof(*sl), NETDEV_ALIGN) + sizeof(struct can_ml_priv);
-	dev = alloc_netdev(size, name, NET_NAME_UNKNOWN, slc_setup);
+	dev = alloc_candev(sizeof(*sl), 1);
 	if (!dev)
 		return NULL;
 
+	snprintf(dev->name, sizeof(dev->name), "slcan%d", i);
+	dev->netdev_ops = &slc_netdev_ops;
 	dev->base_addr  = i;
 	sl = netdev_priv(dev);
-	can_ml = (void *)sl + ALIGN(sizeof(*sl), NETDEV_ALIGN);
-	can_set_ml_priv(dev, can_ml);
 
 	/* Initialize channel control data */
 	sl->magic = SLCAN_MAGIC;
@@ -568,11 +563,7 @@ static int slcan_open(struct tty_struct *tty)
 	if (tty->ops->write == NULL)
 		return -EOPNOTSUPP;
 
-	/* RTnetlink lock is misused here to serialize concurrent
-	   opens of slcan channels. There are better ways, but it is
-	   the simplest one.
-	 */
-	rtnl_lock();
+	spin_lock(&slcan_lock);
 
 	/* Collect hanged up channels. */
 	slc_sync();
@@ -600,13 +591,15 @@ static int slcan_open(struct tty_struct *tty)
 
 		set_bit(SLF_INUSE, &sl->flags);
 
-		err = register_netdevice(sl->dev);
-		if (err)
+		err = register_candev(sl->dev);
+		if (err) {
+			pr_err("slcan: can't register candev\n");
 			goto err_free_chan;
+		}
 	}
 
 	/* Done.  We have linked the TTY line to a channel. */
-	rtnl_unlock();
+	spin_unlock(&slcan_lock);
 	tty->receive_room = 65536;	/* We don't flow control */
 
 	/* TTY layer expects 0 on success */
@@ -616,14 +609,10 @@ static int slcan_open(struct tty_struct *tty)
 	sl->tty = NULL;
 	tty->disc_data = NULL;
 	clear_bit(SLF_INUSE, &sl->flags);
-	slc_free_netdev(sl->dev);
-	/* do not call free_netdev before rtnl_unlock */
-	rtnl_unlock();
-	free_netdev(sl->dev);
-	return err;
+	slc_dealloc(sl);
 
 err_exit:
-	rtnl_unlock();
+	spin_unlock(&slcan_lock);
 
 	/* Count references from TTY module */
 	return err;
@@ -653,9 +642,11 @@ static void slcan_close(struct tty_struct *tty)
 	synchronize_rcu();
 	flush_work(&sl->tx_work);
 
-	/* Flush network side */
-	unregister_netdev(sl->dev);
-	/* This will complete via sl_free_netdev */
+	slc_close(sl->dev);
+	unregister_candev(sl->dev);
+	spin_lock(&slcan_lock);
+	slc_dealloc(sl);
+	spin_unlock(&slcan_lock);
 }
 
 static void slcan_hangup(struct tty_struct *tty)
@@ -763,18 +754,29 @@ static void __exit slcan_exit(void)
 		dev = slcan_devs[i];
 		if (!dev)
 			continue;
-		slcan_devs[i] = NULL;
 
-		sl = netdev_priv(dev);
-		if (sl->tty) {
-			netdev_err(dev, "tty discipline still running\n");
-		}
+		spin_lock(&slcan_lock);
+		dev = slcan_devs[i];
+		if (dev) {
+			slcan_devs[i] = NULL;
+			spin_unlock(&slcan_lock);
+			sl = netdev_priv(dev);
+			if (sl->tty) {
+				netdev_err(dev,
+					   "tty discipline still running\n");
+			}
 
-		unregister_netdev(dev);
+			slc_close(dev);
+			unregister_candev(dev);
+		} else {
+			spin_unlock(&slcan_lock);
+		}
 	}
 
+	spin_lock(&slcan_lock);
 	kfree(slcan_devs);
 	slcan_devs = NULL;
+	spin_unlock(&slcan_lock);
 
 	tty_unregister_ldisc(&slc_ldisc);
 }
-- 
2.32.0