[RESEND PATCH v2] can: peak_usb: export PCAN device ID as sysfs device attribute

[Lukas Magel <lukas.magel@posteo.net>]

Peak USB devices support a configurable u8 / u32 device ID. In
multi-device setups, this device ID can be configured and used to
identify individual CAN interfaces independent of the order in which
they are plugged into the system. At the current time, the device ID
is already queried from the device and stored in the peak_usb_device
struct.

This patch exports the device ID (called device_number in the struct)
as a sysfs attribute. The attribute name was chosen to be device_id
instead of device_number because the latter has been deprecated by Peak
in their API.

Signed-off-by: Lukas Magel <lukas.magel@posteo.net>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
CC: Stephane Grosjean <s.grosjean@peak-system.com>
---
V2: Update netdev_warn to output the mnemonic of the error value

Resubmission of the patch. Also added Stéphane as maintainer in CC.

 drivers/net/can/usb/peak_usb/pcan_usb_core.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/net/can/usb/peak_usb/pcan_usb_core.c b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
index 27b0a72fd885..7af3dd0a1b35 100644
--- a/drivers/net/can/usb/peak_usb/pcan_usb_core.c
+++ b/drivers/net/can/usb/peak_usb/pcan_usb_core.c
@@ -15,6 +15,8 @@
 #include <linux/netdevice.h>
 #include <linux/usb.h>
 #include <linux/ethtool.h>
+#include <linux/device.h>
+#include <linux/sysfs.h>
 
 #include <linux/can.h>
 #include <linux/can/dev.h>
@@ -53,6 +55,15 @@ static const struct usb_device_id peak_usb_table[] = {
 
 MODULE_DEVICE_TABLE(usb, peak_usb_table);
 
+static ssize_t device_id_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct net_device *netdev = to_net_dev(dev);
+	struct peak_usb_device *peak_dev = netdev_priv(netdev);
+
+	return sysfs_emit(buf, "%08X\n", peak_dev->device_number);
+}
+static DEVICE_ATTR_RO(device_id);
+
 /*
  * dump memory
  */
@@ -887,6 +898,11 @@ static int peak_usb_create_dev(const struct peak_usb_adapter *peak_usb_adapter,
 	netdev_info(netdev, "attached to %s channel %u (device %u)\n",
 			peak_usb_adapter->name, ctrl_idx, dev->device_number);
 
+	err = device_create_file(&netdev->dev, &dev_attr_device_id);
+	/* Do not error out since device was configured successfully */
+	if (err)
+		netdev_warn(netdev, "unable to expose device_id via sysfs: %pe\n", ERR_PTR(err));
+
 	return 0;
 
 adap_dev_free:
@@ -923,6 +939,8 @@ static void peak_usb_disconnect(struct usb_interface *intf)
 		dev->state &= ~PCAN_USB_STATE_CONNECTED;
 		strlcpy(name, netdev->name, IFNAMSIZ);
 
+		device_remove_file(&netdev->dev, &dev_attr_device_id);
+
 		unregister_netdev(netdev);
 
 		kfree(dev->cmd_buf);
-- 
2.37.1