/*
 * 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, when using firmwares <= v1.3, 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
 * firmwares >= 1.4 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 (firmware <= 1.3)
 * i2400m_net_erx         Called by the RX code when a data frame is
 *                        available (firmware >= 1.4).
 * 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
netdev_tx_t i2400m_hard_start_xmit(struct sk_buff *skb,
                                         struct net_device *net_dev)
{
        struct i2400m *i2400m = net_dev_to_i2400m(net_dev);
        struct device *dev = i2400m_dev(i2400m);
        int result;

        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);

        d_fnend(3, dev, "(skb %p net_dev %p)\n", skb, net_dev);
        return NETDEV_TX_OK;
}


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. Fake it with the given
 * protocol.
 */
static
void i2400m_rx_fake_eth_header(struct net_device *net_dev,
                               void *_eth_hdr, __be16 protocol)
{
        struct i2400m *i2400m = net_dev_to_i2400m(net_dev);
        struct ethhdr *eth_hdr = _eth_hdr;

        memcpy(eth_hdr->h_dest, net_dev->dev_addr, sizeof(eth_hdr->h_dest));
        memcpy(eth_hdr->h_source, i2400m->src_mac_addr,
               sizeof(eth_hdr->h_source));
        eth_hdr->h_proto = protocol;
}


/*
 * 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
 *
 * This is only used now for the v1.3 firmware. It will be deprecated
 * in >= 2.6.31.
 *
 * Note that due to firmware limitations, we don't have space to add
 * an ethernet header, so we need to copy each packet. Firmware
 * versions >= v1.4 fix this [see i2400m_net_erx()].
 *
 * 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,
                                  cpu_to_be16(ETH_P_IP));
        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_net_erx - pass a network packet to the stack (extended version)
 *
 * @i2400m: device descriptor
 * @skb: the skb where the packet is - the skb should be set to point
 *     at the IP packet; this function will add ethernet headers if
 *     needed.
 * @cs: packet type
 *
 * This is only used now for firmware >= v1.4. Note it is quite
 * similar to i2400m_net_rx() (used only for v1.3 firmware).
 *
 * 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.
 */
void i2400m_net_erx(struct i2400m *i2400m, struct sk_buff *skb,
                    enum i2400m_cs cs)
{
        struct net_device *net_dev = i2400m->wimax_dev.net_dev;
        struct device *dev = i2400m_dev(i2400m);
        int protocol;

        d_fnstart(2, dev, "(i2400m %p skb %p [%u] cs %d)\n",
                  i2400m, skb, skb->len, cs);
        switch(cs) {
        case I2400M_CS_IPV4_0:
        case I2400M_CS_IPV4:
                protocol = ETH_P_IP;
                i2400m_rx_fake_eth_header(i2400m->wimax_dev.net_dev,
                                          skb->data - ETH_HLEN,
                                          cpu_to_be16(ETH_P_IP));
                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 += skb->len;
                break;
        default:
                dev_err(dev, "ERX: BUG? CS type %u unsupported\n", cs);
                goto error;

        }
        d_printf(3, dev, "ERX: receiving %d bytes to the network stack\n",
                 skb->len);
        d_dump(4, dev, skb->data, skb->len);
        netif_rx_ni(skb);       /* see notes in function header */
error:
        d_fnend(2, dev, "(i2400m %p skb %p [%u] cs %d) = void\n",
                i2400m, skb, skb->len, cs);
}

static const struct net_device_ops i2400m_netdev_ops = {
        .ndo_open = i2400m_open,
        .ndo_stop = i2400m_stop,
        .ndo_start_xmit = i2400m_hard_start_xmit,
        .ndo_tx_timeout = i2400m_tx_timeout,
        .ndo_change_mtu = i2400m_change_mtu,
};


/**
 * 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->netdev_ops = &i2400m_netdev_ops;
        d_fnend(3, NULL, "(net_dev %p) = void\n", net_dev);
}
EXPORT_SYMBOL_GPL(i2400m_netdev_setup);