[RFC PATCH 06/13] can: slcan: allow to send commands to the adapter

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

This is a preparation patch for the upcoming support to change the
bitrate via ip tool, reset the adapter error states via the ethtool API
and, more generally, send commands to the adapter.

Since some commands (e. g. setting the bitrate) will be sent before
calling the open_candev(), the netif_running() will return false and so
a new flag bit (i. e. SLF_XCMD) for serial transmission has to be added.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
---

 drivers/net/can/slcan.c | 46 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
index 4df0455e11a2..dbd4ebdfa024 100644
--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -97,6 +97,9 @@ struct slcan {
 	unsigned long		flags;		/* Flag values/ mode etc     */
 #define SLF_INUSE		0		/* Channel in use            */
 #define SLF_ERROR		1               /* Parity, etc. error        */
+#define SLF_XCMD		2               /* Command transmission      */
+	wait_queue_head_t       xcmd_wait;      /* Wait queue for commands   */
+						/* transmission              */
 };
 
 static struct net_device **slcan_devs;
@@ -310,12 +313,22 @@ static void slcan_transmit(struct work_struct *work)
 
 	spin_lock_bh(&sl->lock);
 	/* First make sure we're connected. */
-	if (!sl->tty || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev)) {
+	if (!sl->tty || sl->magic != SLCAN_MAGIC ||
+	    (unlikely(!netif_running(sl->dev)) &&
+	     likely(!test_bit(SLF_XCMD, &sl->flags)))) {
 		spin_unlock_bh(&sl->lock);
 		return;
 	}
 
 	if (sl->xleft <= 0)  {
+		if (unlikely(test_bit(SLF_XCMD, &sl->flags))) {
+			clear_bit(SLF_XCMD, &sl->flags);
+			clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+			spin_unlock_bh(&sl->lock);
+			wake_up(&sl->xcmd_wait);
+			return;
+		}
+
 		/* Now serial buffer is almost free & we can start
 		 * transmission of another packet */
 		sl->dev->stats.tx_packets++;
@@ -379,6 +392,36 @@ static netdev_tx_t slc_xmit(struct sk_buff *skb, struct net_device *dev)
  *   Routines looking at netdevice side.
  ******************************************/
 
+static int slcan_transmit_cmd(struct slcan *sl, const unsigned char *cmd)
+{
+	int ret, actual, n;
+
+	spin_lock(&sl->lock);
+	if (sl->tty == NULL) {
+		spin_unlock(&sl->lock);
+		return -ENODEV;
+	}
+
+	n = snprintf(sl->xbuff, sizeof(sl->xbuff), "%s", cmd);
+	set_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
+	actual = sl->tty->ops->write(sl->tty, sl->xbuff, n);
+	sl->xleft = n - actual;
+	sl->xhead = sl->xbuff + actual;
+	set_bit(SLF_XCMD, &sl->flags);
+	spin_unlock(&sl->lock);
+	ret = wait_event_interruptible_timeout(sl->xcmd_wait,
+					       !test_bit(SLF_XCMD, &sl->flags),
+					       HZ);
+	clear_bit(SLF_XCMD, &sl->flags);
+	if (ret == -ERESTARTSYS)
+		return ret;
+
+	if (ret == 0)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
 /* Netdevice UP -> DOWN routine */
 static int slc_close(struct net_device *dev)
 {
@@ -542,6 +585,7 @@ static struct slcan *slc_alloc(void)
 	sl->dev	= dev;
 	spin_lock_init(&sl->lock);
 	INIT_WORK(&sl->tx_work, slcan_transmit);
+	init_waitqueue_head(&sl->xcmd_wait);
 	slcan_devs[i] = dev;
 
 	return sl;
-- 
2.32.0