i2400m: linkage to the networking stack

Implementation of the glue to the network stack so the WiMAX device
shows up as an Ethernet device.

Initially we shot for implementing a Pure IP device -- however, the
world seems to turn around Ethernet devices. Main issues were with the
ISC DHCP client and servers (as they don't understand types other than
Ethernet and Token Ring).

We proceeded to register with IANA the PureIP hw type, so that DHCP
requests could declare such. We also created patches to the main ISC
DHCP versions to support it. However, until all that permeates into
deployments, there is going to be a long time.

So we moved back to wrap Ethernet frames around the PureIP device. At
the time being this has overhead; we need to reallocate with space for
an Ethernet header. The reason is the device-to-host protocol
coalesces many network packets into a single message, so we can't
introduce Ethernet headers without overwriting valid data from other
packets.

Coming-soon versions of the firmware have this issue solved.
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/net/wimax/i2400m/netdev.c

+/*
+ * Intel Wireless WiMAX Connection 2400m
+ * Glue with the networking stack
+ *
+ *
+ * Copyright (C) 2007 Intel Corporation <linux-wimax@intel.com>
+ * Yanir Lubetkin <yanirx.lubetkin@intel.com>
+ * Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version
+ * 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ *
+ * This implements an ethernet device for the i2400m.
+ *
+ * We fake being an ethernet device to simplify the support from user
+ * space and from the other side. The world is (sadly) configured to
+ * take in only Ethernet devices...
+ *
+ * Because of this, currently there is an copy-each-rxed-packet
+ * overhead on the RX path. Each IP packet has to be reallocated to
+ * add an ethernet header (as there is no space in what we get from
+ * the device). This is a known drawback and coming versions of the
+ * device's firmware are being changed to add header space that can be
+ * used to insert the ethernet header without having to reallocate and
+ * copy.
+ *
+ * TX error handling is tricky; because we have to FIFO/queue the
+ * buffers for transmission (as the hardware likes it aggregated), we
+ * just give the skb to the TX subsystem and by the time it is
+ * transmitted, we have long forgotten about it. So we just don't care
+ * too much about it.
+ *
+ * Note that when the device is in idle mode with the basestation, we
+ * need to negotiate coming back up online. That involves negotiation
+ * and possible user space interaction. Thus, we defer to a workqueue
+ * to do all that. By default, we only queue a single packet and drop
+ * the rest, as potentially the time to go back from idle to normal is
+ * long.
+ *
+ * ROADMAP
+ *
+ * i2400m_open         Called on ifconfig up
+ * i2400m_stop         Called on ifconfig down
+ *
+ * i2400m_hard_start_xmit Called by the network stack to send a packet
+ *   i2400m_net_wake_tx	  Wake up device from basestation-IDLE & TX
+ *     i2400m_wake_tx_work
+ *       i2400m_cmd_exit_idle
+ *       i2400m_tx
+ *   i2400m_net_tx        TX a data frame
+ *     i2400m_tx
+ *
+ * i2400m_change_mtu      Called on ifconfig mtu XXX
+ *
+ * i2400m_tx_timeout      Called when the device times out
+ *
+ * i2400m_net_rx          Called by the RX code when a data frame is
+ *                        available.
+ * i2400m_netdev_setup    Called to setup all the netdev stuff from
+ *                        alloc_netdev.
+ */
+#include <linux/if_arp.h>
+#include <linux/netdevice.h>
+#include "i2400m.h"
+
+
+#define D_SUBMODULE netdev
+#include "debug-levels.h"
+
+enum {
+/* netdev interface */
+	/*
+	 * Out of NWG spec (R1_v1.2.2), 3.3.3 ASN Bearer Plane MTU Size
+	 *
+	 * The MTU is 1400 or less
+	 */
+	I2400M_MAX_MTU = 1400,
+	I2400M_TX_TIMEOUT = HZ,
+	I2400M_TX_QLEN = 5,
+};
+
+
+static
+int i2400m_open(struct net_device *net_dev)
+{
+	int result;
+	struct i2400m *i2400m = net_dev_to_i2400m(net_dev);
+	struct device *dev = i2400m_dev(i2400m);
+
+	d_fnstart(3, dev, "(net_dev %p [i2400m %p])\n", net_dev, i2400m);
+	if (i2400m->ready == 0) {
+		dev_err(dev, "Device is still initializing\n");
+		result = -EBUSY;
+	} else
+		result = 0;
+	d_fnend(3, dev, "(net_dev %p [i2400m %p]) = %d\n",
+		net_dev, i2400m, result);
+	return result;
+}
+
+
+/*
+ *
+ * On kernel versions where cancel_work_sync() didn't return anything,
+ * we rely on wake_tx_skb() being non-NULL.
+ */
+static
+int i2400m_stop(struct net_device *net_dev)
+{
+	struct i2400m *i2400m = net_dev_to_i2400m(net_dev);
+	struct device *dev = i2400m_dev(i2400m);
+
+	d_fnstart(3, dev, "(net_dev %p [i2400m %p])\n", net_dev, i2400m);
+	/* See i2400m_hard_start_xmit(), references are taken there
+	 * and here we release them if the work was still
+	 * pending. Note we can't differentiate work not pending vs
+	 * never scheduled, so the NULL check does that. */
+	if (cancel_work_sync(&i2400m->wake_tx_ws) == 0
+	    && i2400m->wake_tx_skb != NULL) {
+		unsigned long flags;
+		struct sk_buff *wake_tx_skb;
+		spin_lock_irqsave(&i2400m->tx_lock, flags);
+		wake_tx_skb = i2400m->wake_tx_skb;	/* compat help */
+		i2400m->wake_tx_skb = NULL;	/* compat help */
+		spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+		i2400m_put(i2400m);
+		kfree_skb(wake_tx_skb);
+	}
+	d_fnend(3, dev, "(net_dev %p [i2400m %p]) = 0\n", net_dev, i2400m);
+	return 0;
+}
+
+
+/*
+ * Wake up the device and transmit a held SKB, then restart the net queue
+ *
+ * When the device goes into basestation-idle mode, we need to tell it
+ * to exit that mode; it will negotiate with the base station, user
+ * space may have to intervene to rehandshake crypto and then tell us
+ * when it is ready to transmit the packet we have "queued". Still we
+ * need to give it sometime after it reports being ok.
+ *
+ * On error, there is not much we can do. If the error was on TX, we
+ * still wake the queue up to see if the next packet will be luckier.
+ *
+ * If _cmd_exit_idle() fails...well, it could be many things; most
+ * commonly it is that something else took the device out of IDLE mode
+ * (for example, the base station). In that case we get an -EILSEQ and
+ * we are just going to ignore that one. If the device is back to
+ * connected, then fine -- if it is someother state, the packet will
+ * be dropped anyway.
+ */
+void i2400m_wake_tx_work(struct work_struct *ws)
+{
+	int result;
+	struct i2400m *i2400m = container_of(ws, struct i2400m, wake_tx_ws);
+	struct device *dev = i2400m_dev(i2400m);
+	struct sk_buff *skb = i2400m->wake_tx_skb;
+	unsigned long flags;
+
+	spin_lock_irqsave(&i2400m->tx_lock, flags);
+	skb = i2400m->wake_tx_skb;
+	i2400m->wake_tx_skb = NULL;
+	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+
+	d_fnstart(3, dev, "(ws %p i2400m %p skb %p)\n", ws, i2400m, skb);
+	result = -EINVAL;
+	if (skb == NULL) {
+		dev_err(dev, "WAKE&TX: skb dissapeared!\n");
+		goto out_put;
+	}
+	result = i2400m_cmd_exit_idle(i2400m);
+	if (result == -EILSEQ)
+		result = 0;
+	if (result < 0) {
+		dev_err(dev, "WAKE&TX: device didn't get out of idle: "
+			"%d\n", result);
+			goto error;
+	}
+	result = wait_event_timeout(i2400m->state_wq,
+				    i2400m->state != I2400M_SS_IDLE, 5 * HZ);
+	if (result == 0)
+		result = -ETIMEDOUT;
+	if (result < 0) {
+		dev_err(dev, "WAKE&TX: error waiting for device to exit IDLE: "
+			"%d\n", result);
+		goto error;
+	}
+	msleep(20);	/* device still needs some time or it drops it */
+	result = i2400m_tx(i2400m, skb->data, skb->len, I2400M_PT_DATA);
+	netif_wake_queue(i2400m->wimax_dev.net_dev);
+error:
+	kfree_skb(skb);	/* refcount transferred by _hard_start_xmit() */
+out_put:
+	i2400m_put(i2400m);
+	d_fnend(3, dev, "(ws %p i2400m %p skb %p) = void [%d]\n",
+		ws, i2400m, skb, result);
+}
+
+
+/*
+ * Prepare the data payload TX header
+ *
+ * The i2400m expects a 4 byte header in front of a data packet.
+ *
+ * Because we pretend to be an ethernet device, this packet comes with
+ * an ethernet header. Pull it and push our header.
+ */
+static
+void i2400m_tx_prep_header(struct sk_buff *skb)
+{
+	struct i2400m_pl_data_hdr *pl_hdr;
+	skb_pull(skb, ETH_HLEN);
+	pl_hdr = (struct i2400m_pl_data_hdr *) skb_push(skb, sizeof(*pl_hdr));
+	pl_hdr->reserved = 0;
+}
+
+
+/*
+ * TX an skb to an idle device
+ *
+ * When the device is in basestation-idle mode, we need to wake it up
+ * and then TX. So we queue a work_struct for doing so.
+ *
+ * We need to get an extra ref for the skb (so it is not dropped), as
+ * well as be careful not to queue more than one request (won't help
+ * at all). If more than one request comes or there are errors, we
+ * just drop the packets (see i2400m_hard_start_xmit()).
+ */
+static
+int i2400m_net_wake_tx(struct i2400m *i2400m, struct net_device *net_dev,
+		       struct sk_buff *skb)
+{
+	int result;
+	struct device *dev = i2400m_dev(i2400m);
+	unsigned long flags;
+
+	d_fnstart(3, dev, "(skb %p net_dev %p)\n", skb, net_dev);
+	if (net_ratelimit()) {
+		d_printf(3, dev, "WAKE&NETTX: "
+			 "skb %p sending %d bytes to radio\n",
+			 skb, skb->len);
+		d_dump(4, dev, skb->data, skb->len);
+	}
+	/* We hold a ref count for i2400m and skb, so when
+	 * stopping() the device, we need to cancel that work
+	 * and if pending, release those resources. */
+	result = 0;
+	spin_lock_irqsave(&i2400m->tx_lock, flags);
+	if (!work_pending(&i2400m->wake_tx_ws)) {
+		netif_stop_queue(net_dev);
+		i2400m_get(i2400m);
+		i2400m->wake_tx_skb = skb_get(skb);	/* transfer ref count */
+		i2400m_tx_prep_header(skb);
+		result = schedule_work(&i2400m->wake_tx_ws);
+		WARN_ON(result == 0);
+	}
+	spin_unlock_irqrestore(&i2400m->tx_lock, flags);
+	if (result == 0) {
+		/* Yes, this happens even if we stopped the
+		 * queue -- blame the queue disciplines that
+		 * queue without looking -- I guess there is a reason
+		 * for that. */
+		if (net_ratelimit())
+			d_printf(1, dev, "NETTX: device exiting idle, "
+				 "dropping skb %p, queue running %d\n",
+				 skb, netif_queue_stopped(net_dev));
+		result = -EBUSY;
+	}
+	d_fnend(3, dev, "(skb %p net_dev %p) = %d\n", skb, net_dev, result);
+	return result;
+}
+
+
+/*
+ * Transmit a packet to the base station on behalf of the network stack.
+ *
+ * Returns: 0 if ok, < 0 errno code on error.
+ *
+ * We need to pull the ethernet header and add the hardware header,
+ * which is currently set to all zeroes and reserved.
+ */
+static
+int i2400m_net_tx(struct i2400m *i2400m, struct net_device *net_dev,
+		  struct sk_buff *skb)
+{
+	int result;
+	struct device *dev = i2400m_dev(i2400m);
+
+	d_fnstart(3, dev, "(i2400m %p net_dev %p skb %p)\n",
+		  i2400m, net_dev, skb);
+	/* FIXME: check eth hdr, only IPv4 is routed by the device as of now */
+	net_dev->trans_start = jiffies;
+	i2400m_tx_prep_header(skb);
+	d_printf(3, dev, "NETTX: skb %p sending %d bytes to radio\n",
+		 skb, skb->len);
+	d_dump(4, dev, skb->data, skb->len);
+	result = i2400m_tx(i2400m, skb->data, skb->len, I2400M_PT_DATA);
+	d_fnend(3, dev, "(i2400m %p net_dev %p skb %p) = %d\n",
+		i2400m, net_dev, skb, result);
+	return result;
+}
+
+
+/*
+ * Transmit a packet to the base station on behalf of the network stack
+ *
+ *
+ * Returns: NETDEV_TX_OK (always, even in case of error)
+ *
+ * In case of error, we just drop it. Reasons:
+ *
+ *  - we add a hw header to each skb, and if the network stack
+ *    retries, we have no way to know if that skb has it or not.
+ *
+ *  - network protocols have their own drop-recovery mechanisms
+ *
+ *  - there is not much else we can do
+ *
+ * If the device is idle, we need to wake it up; that is an operation
+ * that will sleep. See i2400m_net_wake_tx() for details.
+ */
+static
+int i2400m_hard_start_xmit(struct sk_buff *skb,
+			   struct net_device *net_dev)
+{
+	int result;
+	struct i2400m *i2400m = net_dev_to_i2400m(net_dev);
+	struct device *dev = i2400m_dev(i2400m);
+
+	d_fnstart(3, dev, "(skb %p net_dev %p)\n", skb, net_dev);
+	if (i2400m->state == I2400M_SS_IDLE)
+		result = i2400m_net_wake_tx(i2400m, net_dev, skb);
+	else
+		result = i2400m_net_tx(i2400m, net_dev, skb);
+	if (result <  0)
+		net_dev->stats.tx_dropped++;
+	else {
+		net_dev->stats.tx_packets++;
+		net_dev->stats.tx_bytes += skb->len;
+	}
+	kfree_skb(skb);
+	result = NETDEV_TX_OK;
+	d_fnend(3, dev, "(skb %p net_dev %p) = %d\n", skb, net_dev, result);
+	return result;
+}
+
+
+static
+int i2400m_change_mtu(struct net_device *net_dev, int new_mtu)
+{
+	int result;
+	struct i2400m *i2400m = net_dev_to_i2400m(net_dev);
+	struct device *dev = i2400m_dev(i2400m);
+
+	if (new_mtu >= I2400M_MAX_MTU) {
+		dev_err(dev, "Cannot change MTU to %d (max is %d)\n",
+			new_mtu, I2400M_MAX_MTU);
+		result = -EINVAL;
+	} else {
+		net_dev->mtu = new_mtu;
+		result = 0;
+	}
+	return result;
+}
+
+
+static
+void i2400m_tx_timeout(struct net_device *net_dev)
+{
+	/*
+	 * We might want to kick the device
+	 *
+	 * There is not much we can do though, as the device requires
+	 * that we send the data aggregated. By the time we receive
+	 * this, there might be data pending to be sent or not...
+	 */
+	net_dev->stats.tx_errors++;
+	return;
+}
+
+
+/*
+ * Create a fake ethernet header
+ *
+ * For emulating an ethernet device, every received IP header has to
+ * be prefixed with an ethernet header.
+ *
+ * What we receive has (potentially) many IP packets concatenated with
+ * no ETH_HLEN bytes prefixed. Thus there is no space for an eth
+ * header.
+ *
+ * We would have to reallocate or do ugly fragment tricks in order to
+ * add it.
+ *
+ * But what we do is use the header space of the RX transaction
+ * (*msg_hdr) as we don't need it anymore; then we'll point all the
+ * data skbs there, as they share the same backing store.
+ *
+ * We only support IPv4 for v3 firmware.
+ */
+static
+void i2400m_rx_fake_eth_header(struct net_device *net_dev,
+			       void *_eth_hdr)
+{
+	struct ethhdr *eth_hdr = _eth_hdr;
+
+	memcpy(eth_hdr->h_dest, net_dev->dev_addr, sizeof(eth_hdr->h_dest));
+	memset(eth_hdr->h_source, 0, sizeof(eth_hdr->h_dest));
+	eth_hdr->h_proto = __constant_cpu_to_be16(ETH_P_IP);
+}
+
+
+/*
+ * i2400m_net_rx - pass a network packet to the stack
+ *
+ * @i2400m: device instance
+ * @skb_rx: the skb where the buffer pointed to by @buf is
+ * @i: 1 if payload is the only one
+ * @buf: pointer to the buffer containing the data
+ * @len: buffer's length
+ *
+ * We just clone the skb and set it up so that it's skb->data pointer
+ * points to "buf" and it's length.
+ *
+ * Note that if the payload is the last (or the only one) in a
+ * multi-payload message, we don't clone the SKB but just reuse it.
+ *
+ * This function is normally run from a thread context. However, we
+ * still use netif_rx() instead of netif_receive_skb() as was
+ * recommended in the mailing list. Reason is in some stress tests
+ * when sending/receiving a lot of data we seem to hit a softlock in
+ * the kernel's TCP implementation [aroudn tcp_delay_timer()]. Using
+ * netif_rx() took care of the issue.
+ *
+ * This is, of course, still open to do more research on why running
+ * with netif_receive_skb() hits this softlock. FIXME.
+ *
+ * FIXME: currently we don't do any efforts at distinguishing if what
+ * we got was an IPv4 or IPv6 header, to setup the protocol field
+ * correctly.
+ */
+void i2400m_net_rx(struct i2400m *i2400m, struct sk_buff *skb_rx,
+		   unsigned i, const void *buf, int buf_len)
+{
+	struct net_device *net_dev = i2400m->wimax_dev.net_dev;
+	struct device *dev = i2400m_dev(i2400m);
+	struct sk_buff *skb;
+
+	d_fnstart(2, dev, "(i2400m %p buf %p buf_len %d)\n",
+		  i2400m, buf, buf_len);
+	if (i) {
+		skb = skb_get(skb_rx);
+		d_printf(2, dev, "RX: reusing first payload skb %p\n", skb);
+		skb_pull(skb, buf - (void *) skb->data);
+		skb_trim(skb, (void *) skb_end_pointer(skb) - buf);
+	} else {
+		/* Yes, this is bad -- a lot of overhead -- see
+		 * comments at the top of the file */
+		skb = __netdev_alloc_skb(net_dev, buf_len, GFP_KERNEL);
+		if (skb == NULL) {
+			dev_err(dev, "NETRX: no memory to realloc skb\n");
+			net_dev->stats.rx_dropped++;
+			goto error_skb_realloc;
+		}
+		memcpy(skb_put(skb, buf_len), buf, buf_len);
+	}
+	i2400m_rx_fake_eth_header(i2400m->wimax_dev.net_dev,
+				  skb->data - ETH_HLEN);
+	skb_set_mac_header(skb, -ETH_HLEN);
+	skb->dev = i2400m->wimax_dev.net_dev;
+	skb->protocol = htons(ETH_P_IP);
+	net_dev->stats.rx_packets++;
+	net_dev->stats.rx_bytes += buf_len;
+	d_printf(3, dev, "NETRX: receiving %d bytes to network stack\n",
+		buf_len);
+	d_dump(4, dev, buf, buf_len);
+	netif_rx_ni(skb);	/* see notes in function header */
+error_skb_realloc:
+	d_fnend(2, dev, "(i2400m %p buf %p buf_len %d) = void\n",
+		i2400m, buf, buf_len);
+}
+
+
+/**
+ * i2400m_netdev_setup - Setup setup @net_dev's i2400m private data
+ *
+ * Called by alloc_netdev()
+ */
+void i2400m_netdev_setup(struct net_device *net_dev)
+{
+	d_fnstart(3, NULL, "(net_dev %p)\n", net_dev);
+	ether_setup(net_dev);
+	net_dev->mtu = I2400M_MAX_MTU;
+	net_dev->tx_queue_len = I2400M_TX_QLEN;
+	net_dev->features =
+		  NETIF_F_VLAN_CHALLENGED
+		| NETIF_F_HIGHDMA;
+	net_dev->flags =
+		IFF_NOARP		/* i2400m is apure IP device */
+		& (~IFF_BROADCAST	/* i2400m is P2P */
+		   & ~IFF_MULTICAST);
+	net_dev->watchdog_timeo = I2400M_TX_TIMEOUT;
+	net_dev->open = i2400m_open;
+	net_dev->stop = i2400m_stop;
+	net_dev->hard_start_xmit = i2400m_hard_start_xmit;
+	net_dev->change_mtu = i2400m_change_mtu;
+	net_dev->tx_timeout = i2400m_tx_timeout;
+	d_fnend(3, NULL, "(net_dev %p) = void\n", net_dev);
+}
+EXPORT_SYMBOL_GPL(i2400m_netdev_setup);
+