Merge branch 'net-usb-qmi_wwan-new-mux_id-sysfs-file'

Daniele Palmas says:

====================
net: usb: qmi_wwan: new mux_id sysfs file

this patch series add a sysfs file to let userspace know which mux
id has been used to create a qmimux network interface.

I'm aware that adding new sysfs files is not usually the right path,
but my understanding is that this piece of information can't be
retrieved in any other way and its absence restricts how
userspace application (e.g. like libqmi) can take advantage of the
qmimux implementation in qmi_wwan.
====================

Link: https://lore.kernel.org/r/20210127153433.12237-1-dnlplm@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/ABI/testing/sysfs-class-net-qmi

@@ -48,3 +48,13 @@ Description:
 
 		Write a number ranging from 1 to 254 to delete a previously
 		created qmap mux based network device.
+
+What:		/sys/class/net/<qmimux iface>/qmap/mux_id
+Date:		January 2021
+KernelVersion:	5.12
+Contact:	Daniele Palmas <dnlplm@gmail.com>
+Description:
+		Unsigned integer
+
+		Indicates the mux id associated to the qmimux network interface
+		during its creation.

drivers/net/usb/qmi_wwan.c

@@ -218,6 +218,28 @@ static int qmimux_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 	return 1;
 }
 
+static ssize_t mux_id_show(struct device *d, struct device_attribute *attr, char *buf)
+{
+	struct net_device *dev = to_net_dev(d);
+	struct qmimux_priv *priv;
+
+	priv = netdev_priv(dev);
+
+	return sysfs_emit(buf, "0x%02x\n", priv->mux_id);
+}
+
+static DEVICE_ATTR_RO(mux_id);
+
+static struct attribute *qmi_wwan_sysfs_qmimux_attrs[] = {
+	&dev_attr_mux_id.attr,
+	NULL,
+};
+
+static struct attribute_group qmi_wwan_sysfs_qmimux_attr_group = {
+	.name = "qmap",
+	.attrs = qmi_wwan_sysfs_qmimux_attrs,
+};
+
 static int qmimux_register_device(struct net_device *real_dev, u8 mux_id)
 {
 	struct net_device *new_dev;
@@ -240,6 +262,8 @@ static int qmimux_register_device(struct net_device *real_dev, u8 mux_id)
 		goto out_free_newdev;
 	}
 
+	new_dev->sysfs_groups[0] = &qmi_wwan_sysfs_qmimux_attr_group;
+
 	err = register_netdevice(new_dev);
 	if (err < 0)
 		goto out_free_newdev;