[RFC PATCH v3 8/9] can: slcan: add support to set bit time register (btr)

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

It allows to set the bit time register with tunable values.
The setting can only be changed if the interface is down:

ip link set dev can0 down
ethtool --set-tunable can0 can-btr 0x31c
ip link set dev can0 up

Suggested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
---

(no changes since v1)

 drivers/net/can/slcan/slcan-core.c    | 58 ++++++++++++++++++++-------
 drivers/net/can/slcan/slcan-ethtool.c | 13 ++++++
 drivers/net/can/slcan/slcan.h         |  1 +
 3 files changed, 58 insertions(+), 14 deletions(-)

diff --git a/drivers/net/can/slcan/slcan-core.c b/drivers/net/can/slcan/slcan-core.c
index 45e521910236..3905f21e7788 100644
--- a/drivers/net/can/slcan/slcan-core.c
+++ b/drivers/net/can/slcan/slcan-core.c
@@ -99,6 +99,7 @@ struct slcan {
 #define CF_ERR_RST		0               /* Reset errors on open      */
 	wait_queue_head_t       xcmd_wait;      /* Wait queue for commands   */
 						/* transmission              */
+	u32 btr;				/* bit timing register       */
 };
 
 static const u32 slcan_bitrate_const[] = {
@@ -128,6 +129,17 @@ int slcan_enable_err_rst_on_open(struct net_device *ndev, bool on)
 	return 0;
 }
 
+int slcan_set_btr(struct net_device *ndev, u32 btr)
+{
+	struct slcan *sl = netdev_priv(ndev);
+
+	if (netif_running(ndev))
+		return -EBUSY;
+
+	sl->btr = btr;
+	return 0;
+}
+
 /*************************************************************************
  *			SLCAN ENCAPSULATION FORMAT			 *
  *************************************************************************/
@@ -699,22 +711,40 @@ static int slcan_netdev_open(struct net_device *dev)
 		return err;
 	}
 
-	if (sl->can.bittiming.bitrate != CAN_BITRATE_UNKNOWN) {
-		for (s = 0; s < ARRAY_SIZE(slcan_bitrate_const); s++) {
-			if (sl->can.bittiming.bitrate == slcan_bitrate_const[s])
-				break;
+	if (sl->can.bittiming.bitrate != CAN_BITRATE_UNKNOWN || sl->btr) {
+		if (sl->can.bittiming.bitrate != CAN_BITRATE_UNKNOWN) {
+			for (s = 0; s < ARRAY_SIZE(slcan_bitrate_const); s++) {
+				if (sl->can.bittiming.bitrate ==
+				    slcan_bitrate_const[s])
+					break;
+			}
+
+			/* The CAN framework has already validate the bitrate
+			 * value, so we can avoid to check if `s' has been
+			 * properly set.
+			 */
+			snprintf(cmd, sizeof(cmd), "C\rS%d\r", s);
+			err = slcan_transmit_cmd(sl, cmd);
+			if (err) {
+				netdev_err(dev,
+					   "failed to send bitrate command 'C\\rS%d\\r'\n",
+					   s);
+				goto cmd_transmit_failed;
+			}
 		}
 
-		/* The CAN framework has already validate the bitrate value,
-		 * so we can avoid to check if `s' has been properly set.
-		 */
-		snprintf(cmd, sizeof(cmd), "C\rS%d\r", s);
-		err = slcan_transmit_cmd(sl, cmd);
-		if (err) {
-			netdev_err(dev,
-				   "failed to send bitrate command 'C\\rS%d\\r'\n",
-				   s);
-			goto cmd_transmit_failed;
+		if (sl->btr) {
+			u32 btr = sl->btr & GENMASK(15, 0);
+
+			snprintf(cmd, sizeof(cmd), "C\rs%04x\r", btr);
+			err = slcan_transmit_cmd(sl, cmd);
+			if (err) {
+				netdev_err(dev,
+					   "failed to send bit timing command 'C\\rs%04x\\r'\n",
+					   btr);
+				goto cmd_transmit_failed;
+			}
+
 		}
 
 		if (test_bit(CF_ERR_RST, &sl->cmd_flags)) {
diff --git a/drivers/net/can/slcan/slcan-ethtool.c b/drivers/net/can/slcan/slcan-ethtool.c
index bf0afdc4e49d..8e2e77bbffda 100644
--- a/drivers/net/can/slcan/slcan-ethtool.c
+++ b/drivers/net/can/slcan/slcan-ethtool.c
@@ -52,11 +52,24 @@ static int slcan_get_sset_count(struct net_device *netdev, int sset)
 	}
 }
 
+static int slcan_set_tunable(struct net_device *netdev,
+			     const struct ethtool_tunable *tuna,
+			     const void *data)
+{
+	switch (tuna->id) {
+	case ETHTOOL_CAN_BTR:
+		return slcan_set_btr(netdev, *(u32 *)data);
+	default:
+		return -EINVAL;
+	}
+}
+
 static const struct ethtool_ops slcan_ethtool_ops = {
 	.get_strings = slcan_get_strings,
 	.get_priv_flags = slcan_get_priv_flags,
 	.set_priv_flags = slcan_set_priv_flags,
 	.get_sset_count = slcan_get_sset_count,
+	.set_tunable = slcan_set_tunable,
 };
 
 void slcan_set_ethtool_ops(struct net_device *netdev)
diff --git a/drivers/net/can/slcan/slcan.h b/drivers/net/can/slcan/slcan.h
index d463c8d99e22..1ac412fe8c95 100644
--- a/drivers/net/can/slcan/slcan.h
+++ b/drivers/net/can/slcan/slcan.h
@@ -13,6 +13,7 @@
 
 bool slcan_err_rst_on_open(struct net_device *ndev);
 int slcan_enable_err_rst_on_open(struct net_device *ndev, bool on);
+int slcan_set_btr(struct net_device *ndev, u32 btr);
 void slcan_set_ethtool_ops(struct net_device *ndev);
 
 #endif /* _SLCAN_H */
-- 
2.32.0