/*
 * Ethernet interface part of the LG VL600 LTE modem (4G dongle)
 *
 * Copyright (C) 2011 Intel Corporation
 * Author: Andrzej Zaborowski <balrogg@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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, see <http://www.gnu.org/licenses/>.
 */
#include <linux/etherdevice.h>
#include <linux/ethtool.h>
#include <linux/mii.h>
#include <linux/usb.h>
#include <linux/usb/cdc.h>
#include <linux/usb/usbnet.h>
#include <linux/if_ether.h>
#include <linux/if_arp.h>
#include <linux/inetdevice.h>
#include <linux/module.h>

/*
 * The device has a CDC ACM port for modem control (it claims to be
 * CDC ACM anyway) and a CDC Ethernet port for actual network data.
 * It will however ignore data on both ports that is not encapsulated
 * in a specific way, any data returned is also encapsulated the same
 * way.  The headers don't seem to follow any popular standard.
 *
 * This driver adds and strips these headers from the ethernet frames
 * sent/received from the CDC Ethernet port.  The proprietary header
 * replaces the standard ethernet header in a packet so only actual
 * ethernet frames are allowed.  The headers allow some form of
 * multiplexing by using non standard values of the .h_proto field.
 * Windows/Mac drivers do send a couple of such frames to the device
 * during initialisation, with protocol set to 0x0906 or 0x0b06 and (what
 * seems to be) a flag in the .dummy_flags.  This doesn't seem necessary
 * for modem operation but can possibly be used for GPS or other funcitons.
 */

struct vl600_frame_hdr {
        __le32 len;
        __le32 serial;
        __le32 pkt_cnt;
        __le32 dummy_flags;
        __le32 dummy;
        __le32 magic;
} __attribute__((packed));

struct vl600_pkt_hdr {
        __le32 dummy[2];
        __le32 len;
        __be16 h_proto;
} __attribute__((packed));

struct vl600_state {
        struct sk_buff *current_rx_buf;
};

static int vl600_bind(struct usbnet *dev, struct usb_interface *intf)
{
        int ret;
        struct vl600_state *s = kzalloc(sizeof(struct vl600_state), GFP_KERNEL);

        if (!s)
                return -ENOMEM;

        ret = usbnet_cdc_bind(dev, intf);
        if (ret) {
                kfree(s);
                return ret;
        }

        dev->driver_priv = s;

        /* ARP packets don't go through, but they're also of no use.  The
         * subnet has only two hosts anyway: us and the gateway / DHCP
         * server (probably simulated by modem firmware or network operator)
         * whose address changes everytime we connect to the intarwebz and
         * who doesn't bother answering ARP requests either.  So hardware
         * addresses have no meaning, the destination and the source of every
         * packet depend only on whether it is on the IN or OUT endpoint.  */
        dev->net->flags |= IFF_NOARP;
        /* IPv6 NDP relies on multicast.  Enable it by default. */
        dev->net->flags |= IFF_MULTICAST;

        return ret;
}

static void vl600_unbind(struct usbnet *dev, struct usb_interface *intf)
{
        struct vl600_state *s = dev->driver_priv;

        if (s->current_rx_buf)
                dev_kfree_skb(s->current_rx_buf);

        kfree(s);

        return usbnet_cdc_unbind(dev, intf);
}

static int vl600_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
{
        struct vl600_frame_hdr *frame;
        struct vl600_pkt_hdr *packet;
        struct ethhdr *ethhdr;
        int packet_len, count;
        struct sk_buff *buf = skb;
        struct sk_buff *clone;
        struct vl600_state *s = dev->driver_priv;

        /* Frame lengths are generally 4B multiplies but every couple of
         * hours there's an odd number of bytes sized yet correct frame,
         * so don't require this.  */

        /* Allow a packet (or multiple packets batched together) to be
         * split across many frames.  We don't allow a new batch to
         * begin in the same frame another one is ending however, and no
         * leading or trailing pad bytes.  */
        if (s->current_rx_buf) {
                frame = (struct vl600_frame_hdr *) s->current_rx_buf->data;
                if (skb->len + s->current_rx_buf->len >
                                le32_to_cpup(&frame->len)) {
                        netif_err(dev, ifup, dev->net, "Fragment too long\n");
                        dev->net->stats.rx_length_errors++;
                        goto error;
                }

                buf = s->current_rx_buf;
                memcpy(skb_put(buf, skb->len), skb->data, skb->len);
        } else if (skb->len < 4) {
                netif_err(dev, ifup, dev->net, "Frame too short\n");
                dev->net->stats.rx_length_errors++;
                goto error;
        }

        frame = (struct vl600_frame_hdr *) buf->data;
        /* Yes, check that frame->magic == 0x53544448 (or 0x44544d48),
         * otherwise we may run out of memory w/a bad packet */
        if (ntohl(frame->magic) != 0x53544448 &&
                        ntohl(frame->magic) != 0x44544d48)
                goto error;

        if (buf->len < sizeof(*frame) ||
                        buf->len != le32_to_cpup(&frame->len)) {
                /* Save this fragment for later assembly */
                if (s->current_rx_buf)
                        return 0;

                s->current_rx_buf = skb_copy_expand(skb, 0,
                                le32_to_cpup(&frame->len), GFP_ATOMIC);
                if (!s->current_rx_buf) {
                        netif_err(dev, ifup, dev->net, "Reserving %i bytes "
                                        "for packet assembly failed.\n",
                                        le32_to_cpup(&frame->len));
                        dev->net->stats.rx_errors++;
                }

                return 0;
        }

        count = le32_to_cpup(&frame->pkt_cnt);

        skb_pull(buf, sizeof(*frame));

        while (count--) {
                if (buf->len < sizeof(*packet)) {
                        netif_err(dev, ifup, dev->net, "Packet too short\n");
                        goto error;
                }

                packet = (struct vl600_pkt_hdr *) buf->data;
                packet_len = sizeof(*packet) + le32_to_cpup(&packet->len);
                if (packet_len > buf->len) {
                        netif_err(dev, ifup, dev->net,
                                        "Bad packet length stored in header\n");
                        goto error;
                }

                /* Packet header is same size as the ethernet header
                 * (sizeof(*packet) == sizeof(*ethhdr)), additionally
                 * the h_proto field is in the same place so we just leave it
                 * alone and fill in the remaining fields.
                 */
                ethhdr = (struct ethhdr *) skb->data;
                if (be16_to_cpup(&ethhdr->h_proto) == ETH_P_ARP &&
                                buf->len > 0x26) {
                        /* Copy the addresses from packet contents */
                        memcpy(ethhdr->h_source,
                                        &buf->data[sizeof(*ethhdr) + 0x8],
                                        ETH_ALEN);
                        memcpy(ethhdr->h_dest,
                                        &buf->data[sizeof(*ethhdr) + 0x12],
                                        ETH_ALEN);
                } else {
                        eth_zero_addr(ethhdr->h_source);
                        memcpy(ethhdr->h_dest, dev->net->dev_addr, ETH_ALEN);

                        /* Inbound IPv6 packets have an IPv4 ethertype (0x800)
                         * for some reason.  Peek at the L3 header to check
                         * for IPv6 packets, and set the ethertype to IPv6
                         * (0x86dd) so Linux can understand it.
                         */
                        if ((buf->data[sizeof(*ethhdr)] & 0xf0) == 0x60)
                                ethhdr->h_proto = htons(ETH_P_IPV6);
                }

                if (count) {
                        /* Not the last packet in this batch */
                        clone = skb_clone(buf, GFP_ATOMIC);
                        if (!clone)
                                goto error;

                        skb_trim(clone, packet_len);
                        usbnet_skb_return(dev, clone);

                        skb_pull(buf, (packet_len + 3) & ~3);
                } else {
                        skb_trim(buf, packet_len);

                        if (s->current_rx_buf) {
                                usbnet_skb_return(dev, buf);
                                s->current_rx_buf = NULL;
                                return 0;
                        }

                        return 1;
                }
        }

error:
        if (s->current_rx_buf) {
                dev_kfree_skb_any(s->current_rx_buf);
                s->current_rx_buf = NULL;
        }
        dev->net->stats.rx_errors++;
        return 0;
}

static struct sk_buff *vl600_tx_fixup(struct usbnet *dev,
                struct sk_buff *skb, gfp_t flags)
{
        struct sk_buff *ret;
        struct vl600_frame_hdr *frame;
        struct vl600_pkt_hdr *packet;
        static uint32_t serial = 1;
        int orig_len = skb->len - sizeof(struct ethhdr);
        int full_len = (skb->len + sizeof(struct vl600_frame_hdr) + 3) & ~3;

        frame = (struct vl600_frame_hdr *) skb->data;
        if (skb->len > sizeof(*frame) && skb->len == le32_to_cpup(&frame->len))
                return skb; /* Already encapsulated? */

        if (skb->len < sizeof(struct ethhdr))
                /* Drop, device can only deal with ethernet packets */
                return NULL;

        if (!skb_cloned(skb)) {
                int headroom = skb_headroom(skb);
                int tailroom = skb_tailroom(skb);

                if (tailroom >= full_len - skb->len - sizeof(*frame) &&
                                headroom >= sizeof(*frame))
                        /* There's enough head and tail room */
                        goto encapsulate;

                if (headroom + tailroom + skb->len >= full_len) {
                        /* There's enough total room, just readjust */
                        skb->data = memmove(skb->head + sizeof(*frame),
                                        skb->data, skb->len);
                        skb_set_tail_pointer(skb, skb->len);
                        goto encapsulate;
                }
        }

        /* Alloc a new skb with the required size */
        ret = skb_copy_expand(skb, sizeof(struct vl600_frame_hdr), full_len -
                        skb->len - sizeof(struct vl600_frame_hdr), flags);
        dev_kfree_skb_any(skb);
        if (!ret)
                return ret;
        skb = ret;

encapsulate:
        /* Packet header is same size as ethernet packet header
         * (sizeof(*packet) == sizeof(struct ethhdr)), additionally the
         * h_proto field is in the same place so we just leave it alone and
         * overwrite the remaining fields.
         */
        packet = (struct vl600_pkt_hdr *) skb->data;
        /* The VL600 wants IPv6 packets to have an IPv4 ethertype
         * Since this modem only supports IPv4 and IPv6, just set all
         * frames to 0x0800 (ETH_P_IP)
         */
        packet->h_proto = htons(ETH_P_IP);
        memset(&packet->dummy, 0, sizeof(packet->dummy));
        packet->len = cpu_to_le32(orig_len);

        frame = (struct vl600_frame_hdr *) skb_push(skb, sizeof(*frame));
        memset(frame, 0, sizeof(*frame));
        frame->len = cpu_to_le32(full_len);
        frame->serial = cpu_to_le32(serial++);
        frame->pkt_cnt = cpu_to_le32(1);

        if (skb->len < full_len) /* Pad */
                skb_put(skb, full_len - skb->len);

        return skb;
}

static const struct driver_info vl600_info = {
        .description    = "LG VL600 modem",
        .flags          = FLAG_RX_ASSEMBLE | FLAG_WWAN,
        .bind           = vl600_bind,
        .unbind         = vl600_unbind,
        .status         = usbnet_cdc_status,
        .rx_fixup       = vl600_rx_fixup,
        .tx_fixup       = vl600_tx_fixup,
};

static const struct usb_device_id products[] = {
        {
                USB_DEVICE_AND_INTERFACE_INFO(0x1004, 0x61aa, USB_CLASS_COMM,
                                USB_CDC_SUBCLASS_ETHERNET, USB_CDC_PROTO_NONE),
                .driver_info    = (unsigned long) &vl600_info,
        },
        {},     /* End */
};
MODULE_DEVICE_TABLE(usb, products);

static struct usb_driver lg_vl600_driver = {
        .name           = "lg-vl600",
        .id_table       = products,
        .probe          = usbnet_probe,
        .disconnect     = usbnet_disconnect,
        .suspend        = usbnet_suspend,
        .resume         = usbnet_resume,
        .disable_hub_initiated_lpm = 1,
};

module_usb_driver(lg_vl600_driver);

MODULE_AUTHOR("Anrzej Zaborowski");
MODULE_DESCRIPTION("LG-VL600 modem's ethernet link");
MODULE_LICENSE("GPL");