Date:   Mon, 25 Jan 2021 00:33:35 -0700
From:   Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
To:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        stranche@...eaurora.org, aleksander@...ksander.es,
        dnlplm@...il.com, bjorn@...k.no, stephan@...hold.net,
        ejcaruso@...gle.com, andrewlassalle@...gle.com
Cc:     Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Subject: [PATCH net-next v2] net: qmi_wwan: Add pass through mode

Pass through mode is to allow packets in MAP format to be passed
on to the stack. rmnet driver can be used to process and demultiplex
these packets.

Pass through mode can be enabled when the device is in raw ip mode only.
Conversely, raw ip mode cannot be disabled when pass through mode is
enabled.

Userspace can use pass through mode in conjunction with rmnet driver
through the following steps-

1. Enable raw ip mode on qmi_wwan device
2. Enable pass through mode on qmi_wwan device
3. Create a rmnet device with qmi_wwan device as real device using netlink

Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
---
v1->v2: Update commit text and fix the following comments from Bjorn-
Remove locking as no netdev state change is requried since all the
configuration is already done in raw_ip_store.
Check the inverse relationship between raw_ip mode and pass_through mode.
pass_through_mode just sets/resets the flag now.
raw_ip check is not needed when queueing pass_through mode packets as
that is enforced already during the mode configuration.

 drivers/net/usb/qmi_wwan.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
index 7ea113f5..e58a80a 100644
--- a/drivers/net/usb/qmi_wwan.c
+++ b/drivers/net/usb/qmi_wwan.c
@@ -57,6 +57,7 @@ struct qmi_wwan_state {
 enum qmi_wwan_flags {
 	QMI_WWAN_FLAG_RAWIP = 1 << 0,
 	QMI_WWAN_FLAG_MUX = 1 << 1,
+	QMI_WWAN_FLAG_PASS_THROUGH = 1 << 2,
 };
 
 enum qmi_wwan_quirks {
@@ -326,6 +327,13 @@ static ssize_t raw_ip_store(struct device *d,  struct device_attribute *attr, co
 	if (enable == (info->flags & QMI_WWAN_FLAG_RAWIP))
 		return len;
 
+	/* ip mode cannot be cleared when pass through mode is set */
+	if (!enable && (info->flags & QMI_WWAN_FLAG_PASS_THROUGH)) {
+		netdev_err(dev->net,
+			   "Cannot clear ip mode on pass through device\n");
+		return -EINVAL;
+	}
+
 	if (!rtnl_trylock())
 		return restart_syscall();
 
@@ -456,14 +464,59 @@ static ssize_t del_mux_store(struct device *d,  struct device_attribute *attr, c
 	return ret;
 }
 
+static ssize_t pass_through_show(struct device *d,
+				 struct device_attribute *attr, char *buf)
+{
+	struct usbnet *dev = netdev_priv(to_net_dev(d));
+	struct qmi_wwan_state *info;
+
+	info = (void *)&dev->data;
+	return sprintf(buf, "%c\n",
+		       info->flags & QMI_WWAN_FLAG_PASS_THROUGH ? 'Y' : 'N');
+}
+
+static ssize_t pass_through_store(struct device *d,
+				  struct device_attribute *attr,
+				  const char *buf, size_t len)
+{
+	struct usbnet *dev = netdev_priv(to_net_dev(d));
+	struct qmi_wwan_state *info;
+	bool enable;
+
+	if (strtobool(buf, &enable))
+		return -EINVAL;
+
+	info = (void *)&dev->data;
+
+	/* no change? */
+	if (enable == (info->flags & QMI_WWAN_FLAG_PASS_THROUGH))
+		return len;
+
+	/* pass through mode can be set for raw ip devices only */
+	if (!(info->flags & QMI_WWAN_FLAG_RAWIP)) {
+		netdev_err(dev->net,
+			   "Cannot set pass through mode on non ip device\n");
+		return -EINVAL;
+	}
+
+	if (enable)
+		info->flags |= QMI_WWAN_FLAG_PASS_THROUGH;
+	else
+		info->flags &= ~QMI_WWAN_FLAG_PASS_THROUGH;
+
+	return len;
+}
+
 static DEVICE_ATTR_RW(raw_ip);
 static DEVICE_ATTR_RW(add_mux);
 static DEVICE_ATTR_RW(del_mux);
+static DEVICE_ATTR_RW(pass_through);
 
 static struct attribute *qmi_wwan_sysfs_attrs[] = {
 	&dev_attr_raw_ip.attr,
 	&dev_attr_add_mux.attr,
 	&dev_attr_del_mux.attr,
+	&dev_attr_pass_through.attr,
 	NULL,
 };
 
@@ -510,6 +563,11 @@ static int qmi_wwan_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 	if (info->flags & QMI_WWAN_FLAG_MUX)
 		return qmimux_rx_fixup(dev, skb);
 
+	if (info->flags & QMI_WWAN_FLAG_PASS_THROUGH) {
+		skb->protocol = htons(ETH_P_MAP);
+		return (netif_rx(skb) == NET_RX_SUCCESS);
+	}
+
 	switch (skb->data[0] & 0xf0) {
 	case 0x40:
 		proto = htons(ETH_P_IP);
-- 
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