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

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Date:   Tue,  7 Jun 2022 11:47:46 +0200
From:   Dario Binacchi <dario.binacchi@...rulasolutions.com>
To:     linux-kernel@...r.kernel.org
Cc:     Amarula patchwork <linux-amarula@...rulasolutions.com>,
        michael@...rulasolutions.com,
        Dario Binacchi <dario.binacchi@...rulasolutions.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Paolo Abeni <pabeni@...hat.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: [RFC PATCH 07/13] can: slcan: set bitrate by CAN device driver API

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@...rulasolutions.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