[RFC PATCH 07/13] can: slcan: set bitrate by CAN device driver API

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

It allows to set the bitrate via ip tool, as it happens for the other
CAN device drivers. It still remains possible to set the bitrate via
slcand or slcan_attach utilities. In case the ip tool is used, the
driver will send the serial command to the adapter.

The struct can_bittiming_const and struct can_priv::clock.freq has been
set with empirical values ​​that allow you to get a correct bit timing, so
that the slc_do_set_bittiming() can be called.

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

---
DTS properties could be used to set the can.clock.freq and the
can.bittiming_const variables. This way the parameters could be changed
based on the type of the adapter.

 drivers/net/can/slcan.c | 54 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
index dbd4ebdfa024..f1bf32b70c4d 100644
--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -105,6 +105,18 @@ struct slcan {
 static struct net_device **slcan_devs;
 static DEFINE_SPINLOCK(slcan_lock);
 
+static const struct can_bittiming_const slcan_bittiming_const = {
+	.name = KBUILD_MODNAME,
+	.tseg1_min = 2,
+	.tseg1_max = 256,
+	.tseg2_min = 1,
+	.tseg2_max = 128,
+	.sjw_max = 128,
+	.brp_min = 1,
+	.brp_max = 256,
+	.brp_inc = 1,
+};
+
  /************************************************************************
   *			SLCAN ENCAPSULATION FORMAT			 *
   ************************************************************************/
@@ -435,6 +447,7 @@ static int slc_close(struct net_device *dev)
 	netif_stop_queue(dev);
 	close_candev(dev);
 	sl->can.state = CAN_STATE_STOPPED;
+	sl->can.bittiming.bitrate = 0;
 	sl->rcount   = 0;
 	sl->xleft    = 0;
 	spin_unlock_bh(&sl->lock);
@@ -456,7 +469,9 @@ static int slc_open(struct net_device *dev)
 	 * can.bittiming.bitrate is 0, causing open_candev() to fail.
 	 * So let's set to a fake value.
 	 */
-	sl->can.bittiming.bitrate = -1;
+	if (sl->can.bittiming.bitrate == 0)
+		sl->can.bittiming.bitrate = -1UL;
+
 	err = open_candev(dev);
 	if (err) {
 		netdev_err(dev, "failed to open can device\n");
@@ -554,6 +569,40 @@ static void slc_sync(void)
 	}
 }
 
+static int slc_do_set_bittiming(struct net_device *dev)
+{
+	struct slcan *sl = netdev_priv(dev);
+	unsigned char cmd[SLC_MTU];
+	int i, s = -1, err;
+	unsigned int bitrates[] = {
+		10000, 20000, 50000, 100000,
+		125000, 250000, 500000, 800000,
+		1000000,
+	};
+
+	for (i = 0; i < ARRAY_SIZE(bitrates); i++) {
+		if (sl->can.bittiming.bitrate == bitrates[i]) {
+			s = i;
+			break;
+		}
+	}
+
+	if (s < 0) {
+		netdev_err(dev, "invalid bitrate\n");
+		return -EINVAL;
+	}
+
+	snprintf(cmd, sizeof(cmd), "C\rS%d\r", s);
+	err = slcan_transmit_cmd(sl, cmd);
+	if (err) {
+		sl->can.bittiming.bitrate = 0;
+		netdev_err(sl->dev,
+			   "failed to send bitrate command 'C\\rS%d\\r'\n", s);
+	}
+
+	return err;
+}
+
 /* Find a free SLCAN channel, and link in this `tty' line. */
 static struct slcan *slc_alloc(void)
 {
@@ -583,6 +632,9 @@ static struct slcan *slc_alloc(void)
 	/* Initialize channel control data */
 	sl->magic = SLCAN_MAGIC;
 	sl->dev	= dev;
+	sl->can.clock.freq = 24 * 1000 * 1000;
+	sl->can.bittiming_const = &slcan_bittiming_const;
+	sl->can.do_set_bittiming = slc_do_set_bittiming;
 	spin_lock_init(&sl->lock);
 	INIT_WORK(&sl->tx_work, slcan_transmit);
 	init_waitqueue_head(&sl->xcmd_wait);
-- 
2.32.0