[RFC PATCH 11/13] can: slcan: add ethtool support to reset adapter errors

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

This patch adds a private flag to the slcan driver to switch the
"err-rst-on-open" setting on and off.

"err-rst-on-open" on  - Reset error states on opening command

"err-rst-on-open" off - Don't reset error states on opening command
                        (default)

The setting can only be changed if the interface is down:

    ip link set dev can0 down
    ethtool --set-priv-flags can0 err-rst-on-open {off|on}
    ip link set dev can0 up

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

 drivers/net/can/slcan/Makefile        |  1 +
 drivers/net/can/slcan/slcan-core.c    | 36 +++++++++++++++
 drivers/net/can/slcan/slcan-ethtool.c | 65 +++++++++++++++++++++++++++
 drivers/net/can/slcan/slcan.h         | 18 ++++++++
 4 files changed, 120 insertions(+)
 create mode 100644 drivers/net/can/slcan/slcan-ethtool.c
 create mode 100644 drivers/net/can/slcan/slcan.h

diff --git a/drivers/net/can/slcan/Makefile b/drivers/net/can/slcan/Makefile
index 2e84f7bf7617..8a88e484ee21 100644
--- a/drivers/net/can/slcan/Makefile
+++ b/drivers/net/can/slcan/Makefile
@@ -4,3 +4,4 @@ obj-$(CONFIG_CAN_SLCAN) += slcan.o
 
 slcan-objs :=
 slcan-objs += slcan-core.o
+slcan-objs += slcan-ethtool.o
diff --git a/drivers/net/can/slcan/slcan-core.c b/drivers/net/can/slcan/slcan-core.c
index d63d270d21da..b813a59534a3 100644
--- a/drivers/net/can/slcan/slcan-core.c
+++ b/drivers/net/can/slcan/slcan-core.c
@@ -57,6 +57,8 @@
 #include <linux/can/dev.h>
 #include <linux/can/skb.h>
 
+#include "slcan.h"
+
 MODULE_ALIAS_LDISC(N_SLCAN);
 MODULE_DESCRIPTION("serial line CAN interface");
 MODULE_LICENSE("GPL");
@@ -98,6 +100,8 @@ struct slcan {
 #define SLF_INUSE		0		/* Channel in use            */
 #define SLF_ERROR		1               /* Parity, etc. error        */
 #define SLF_XCMD		2               /* Command transmission      */
+	unsigned long           cmd_flags;      /* Command flags             */
+#define CF_ERR_RST		0               /* Reset errors on open      */
 	wait_queue_head_t       xcmd_wait;      /* Wait queue for commands   */
 						/* transmission              */
 };
@@ -117,6 +121,28 @@ static const struct can_bittiming_const slcan_bittiming_const = {
 	.brp_inc = 1,
 };
 
+bool slcan_err_rst_on_open(struct net_device *ndev)
+{
+	struct slcan *sl = netdev_priv(ndev);
+
+	return !!test_bit(CF_ERR_RST, &sl->cmd_flags);
+}
+
+int slcan_enable_err_rst_on_open(struct net_device *ndev, bool on)
+{
+	struct slcan *sl = netdev_priv(ndev);
+
+	if (netif_running(ndev))
+		return -EBUSY;
+
+	if (on)
+		set_bit(CF_ERR_RST, &sl->cmd_flags);
+	else
+		clear_bit(CF_ERR_RST, &sl->cmd_flags);
+
+	return 0;
+}
+
  /************************************************************************
   *			SLCAN ENCAPSULATION FORMAT			 *
   ************************************************************************/
@@ -483,6 +509,15 @@ static int slc_open(struct net_device *dev)
 	if (sl->can.bittiming.bitrate == 0) {
 		sl->can.bittiming.bitrate = -1UL;
 	} else {
+		if (test_bit(CF_ERR_RST, &sl->cmd_flags)) {
+			err = slcan_transmit_cmd(sl, "F\r");
+			if (err) {
+				netdev_err(sl->dev,
+					   "failed to send error command 'F\\r'\n");
+				return err;
+			}
+		}
+
 		err = slcan_transmit_cmd(sl, "O\r");
 		if (err) {
 			netdev_err(dev, "failed to send open command 'O\\r'\n");
@@ -645,6 +680,7 @@ static struct slcan *slc_alloc(void)
 
 	snprintf(dev->name, sizeof(dev->name), "slcan%d", i);
 	dev->netdev_ops = &slc_netdev_ops;
+	slcan_set_ethtool_ops(dev);
 	sl = netdev_priv(dev);
 
 	/* Initialize channel control data */
diff --git a/drivers/net/can/slcan/slcan-ethtool.c b/drivers/net/can/slcan/slcan-ethtool.c
new file mode 100644
index 000000000000..bf0afdc4e49d
--- /dev/null
+++ b/drivers/net/can/slcan/slcan-ethtool.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* Copyright (c) 2022 Amarula Solutions, Dario Binacchi <dario.binacchi@amarulasolutions.com>
+ *
+ */
+
+#include <linux/can/dev.h>
+#include <linux/ethtool.h>
+#include <linux/kernel.h>
+#include <linux/netdevice.h>
+#include <linux/platform_device.h>
+
+#include "slcan.h"
+
+static const char slcan_priv_flags_strings[][ETH_GSTRING_LEN] = {
+#define SLCAN_PRIV_FLAGS_ERR_RST_ON_OPEN BIT(0)
+	"err-rst-on-open",
+};
+
+static void slcan_get_strings(struct net_device *ndev, u32 stringset, u8 *data)
+{
+	switch (stringset) {
+	case ETH_SS_PRIV_FLAGS:
+		memcpy(data, slcan_priv_flags_strings,
+		       sizeof(slcan_priv_flags_strings));
+	}
+}
+
+static u32 slcan_get_priv_flags(struct net_device *ndev)
+{
+	u32 flags = 0;
+
+	if (slcan_err_rst_on_open(ndev))
+		flags |= SLCAN_PRIV_FLAGS_ERR_RST_ON_OPEN;
+
+	return flags;
+}
+
+static int slcan_set_priv_flags(struct net_device *ndev, u32 flags)
+{
+	bool err_rst_op_open = !!(flags & SLCAN_PRIV_FLAGS_ERR_RST_ON_OPEN);
+
+	return slcan_enable_err_rst_on_open(ndev, err_rst_op_open);
+}
+
+static int slcan_get_sset_count(struct net_device *netdev, int sset)
+{
+	switch (sset) {
+	case ETH_SS_PRIV_FLAGS:
+		return ARRAY_SIZE(slcan_priv_flags_strings);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+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,
+};
+
+void slcan_set_ethtool_ops(struct net_device *netdev)
+{
+	netdev->ethtool_ops = &slcan_ethtool_ops;
+}
diff --git a/drivers/net/can/slcan/slcan.h b/drivers/net/can/slcan/slcan.h
new file mode 100644
index 000000000000..d463c8d99e22
--- /dev/null
+++ b/drivers/net/can/slcan/slcan.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * slcan.h - serial line CAN interface driver
+ *
+ * Copyright (C) Laurence Culhane <loz@holmes.demon.co.uk>
+ * Copyright (C) Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
+ * Copyright (C) Oliver Hartkopp <socketcan@hartkopp.net>
+ * Copyright (C) 2022 Amarula Solutions, Dario Binacchi <dario.binacchi@amarulasolutions.com>
+ *
+ */
+
+#ifndef _SLCAN_H
+#define _SLCAN_H
+
+bool slcan_err_rst_on_open(struct net_device *ndev);
+int slcan_enable_err_rst_on_open(struct net_device *ndev, bool on);
+void slcan_set_ethtool_ops(struct net_device *ndev);
+
+#endif /* _SLCAN_H */
-- 
2.32.0