// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * USB network interface driver for Samsung Kalmia based LTE USB modem like the
 * Samsung GT-B3730 and GT-B3710.
 *
 * Copyright (C) 2011 Marius Bjoernstad Kotsbak <marius@kotsbak.com>
 *
 * Sponsored by Quicklink Video Distribution Services Ltd.
 *
 * Based on the cdc_eem module.
 */

#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/ctype.h>
#include <linux/ethtool.h>
#include <linux/workqueue.h>
#include <linux/mii.h>
#include <linux/usb.h>
#include <linux/crc32.h>
#include <linux/usb/cdc.h>
#include <linux/usb/usbnet.h>
#include <linux/gfp.h>

/*
 * The Samsung Kalmia based LTE USB modems have a CDC ACM port for modem control
 * handled by the "option" module and an ethernet data port handled by this
 * module.
 *
 * The stick must first be switched into modem mode by usb_modeswitch
 * or similar tool. Then the modem gets sent two initialization packets by
 * this module, which gives the MAC address of the device. User space can then
 * connect the modem using AT commands through the ACM port and then use
 * DHCP on the network interface exposed by this module. Network packets are
 * sent to and from the modem in a proprietary format discovered after watching
 * the behavior of the windows driver for the modem.
 *
 * More information about the use of the modem is available in usb_modeswitch
 * forum and the project page:
 *
 * http://www.draisberghof.de/usb_modeswitch/bb/viewtopic.php?t=465
 * https://github.com/mkotsbak/Samsung-GT-B3730-linux-driver
 */

/* #define      DEBUG */
/* #define      VERBOSE */

#define KALMIA_HEADER_LENGTH 6
#define KALMIA_ALIGN_SIZE 4
#define KALMIA_USB_TIMEOUT 10000

/*-------------------------------------------------------------------------*/

static int
kalmia_send_init_packet(struct usbnet *dev, u8 *init_msg, u8 init_msg_len,
        u8 *buffer, u8 expected_len)
{
        int act_len;
        int status;

        netdev_dbg(dev->net, "Sending init packet");

        status = usb_bulk_msg(dev->udev, usb_sndbulkpipe(dev->udev, 0x02),
                init_msg, init_msg_len, &act_len, KALMIA_USB_TIMEOUT);
        if (status != 0) {
                netdev_err(dev->net,
                        "Error sending init packet. Status %i\n",
                        status);
                return status;
        }
        else if (act_len != init_msg_len) {
                netdev_err(dev->net,
                        "Did not send all of init packet. Bytes sent: %i",
                        act_len);
        }
        else {
                netdev_dbg(dev->net, "Successfully sent init packet.");
        }

        status = usb_bulk_msg(dev->udev, usb_rcvbulkpipe(dev->udev, 0x81),
                buffer, expected_len, &act_len, KALMIA_USB_TIMEOUT);

        if (status != 0)
                netdev_err(dev->net,
                        "Error receiving init result. Status %i\n",
                        status);
        else if (act_len != expected_len)
                netdev_err(dev->net, "Unexpected init result length: %i\n",
                        act_len);

        return status;
}

static int
kalmia_init_and_get_ethernet_addr(struct usbnet *dev, u8 *ethernet_addr)
{
        static const char init_msg_1[] =
                { 0x57, 0x50, 0x04, 0x00, 0x00, 0x00, 0x00, 0x20, 0x00, 0x00,
                0x00, 0x00 };
        static const char init_msg_2[] =
                { 0x57, 0x50, 0x04, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0xf4,
                0x00, 0x00 };
        static const int buflen = 28;
        char *usb_buf;
        int status;

        usb_buf = kmalloc(buflen, GFP_DMA | GFP_KERNEL);
        if (!usb_buf)
                return -ENOMEM;

        memcpy(usb_buf, init_msg_1, 12);
        status = kalmia_send_init_packet(dev, usb_buf, ARRAY_SIZE(init_msg_1),
                                         usb_buf, 24);
        if (status != 0)
                goto out;

        memcpy(usb_buf, init_msg_2, 12);
        status = kalmia_send_init_packet(dev, usb_buf, ARRAY_SIZE(init_msg_2),
                                         usb_buf, 28);
        if (status != 0)
                goto out;

        memcpy(ethernet_addr, usb_buf + 10, ETH_ALEN);
out:
        kfree(usb_buf);
        return status;
}

static int
kalmia_bind(struct usbnet *dev, struct usb_interface *intf)
{
        int status;
        u8 ethernet_addr[ETH_ALEN];
        static const u8 ep_addr[] = {
                1 | USB_DIR_IN,
                2 | USB_DIR_OUT,
                0};

        /* Don't bind to AT command interface */
        if (intf->cur_altsetting->desc.bInterfaceClass != USB_CLASS_VENDOR_SPEC)
                return -EINVAL;

        if (!usb_check_bulk_endpoints(intf, ep_addr))
                return -ENODEV;

        dev->in = usb_rcvbulkpipe(dev->udev, 0x81 & USB_ENDPOINT_NUMBER_MASK);
        dev->out = usb_sndbulkpipe(dev->udev, 0x02 & USB_ENDPOINT_NUMBER_MASK);
        dev->status = NULL;

        dev->net->hard_header_len += KALMIA_HEADER_LENGTH;
        dev->hard_mtu = 1400;
        dev->rx_urb_size = dev->hard_mtu * 10; // Found as optimal after testing

        status = kalmia_init_and_get_ethernet_addr(dev, ethernet_addr);
        if (status)
                return status;

        eth_hw_addr_set(dev->net, ethernet_addr);

        return status;
}

static struct sk_buff *
kalmia_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
{
        struct sk_buff *skb2 = NULL;
        u16 content_len;
        unsigned char *header_start;
        unsigned char ether_type_1, ether_type_2;
        u8 remainder, padlen = 0;

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

                if ((tailroom >= KALMIA_ALIGN_SIZE) && (headroom
                        >= KALMIA_HEADER_LENGTH))
                        goto done;

                if ((headroom + tailroom) > (KALMIA_HEADER_LENGTH
                        + KALMIA_ALIGN_SIZE)) {
                        skb->data = memmove(skb->head + KALMIA_HEADER_LENGTH,
                                skb->data, skb->len);
                        skb_set_tail_pointer(skb, skb->len);
                        goto done;
                }
        }

        skb2 = skb_copy_expand(skb, KALMIA_HEADER_LENGTH,
                KALMIA_ALIGN_SIZE, flags);
        if (!skb2)
                return NULL;

        dev_kfree_skb_any(skb);
        skb = skb2;

done:
        header_start = skb_push(skb, KALMIA_HEADER_LENGTH);
        ether_type_1 = header_start[KALMIA_HEADER_LENGTH + 12];
        ether_type_2 = header_start[KALMIA_HEADER_LENGTH + 13];

        netdev_dbg(dev->net, "Sending etherType: %02x%02x", ether_type_1,
                ether_type_2);

        /* According to empiric data for data packages */
        header_start[0] = 0x57;
        header_start[1] = 0x44;
        content_len = skb->len - KALMIA_HEADER_LENGTH;

        put_unaligned_le16(content_len, &header_start[2]);
        header_start[4] = ether_type_1;
        header_start[5] = ether_type_2;

        /* Align to 4 bytes by padding with zeros */
        remainder = skb->len % KALMIA_ALIGN_SIZE;
        if (remainder > 0) {
                padlen = KALMIA_ALIGN_SIZE - remainder;
                skb_put_zero(skb, padlen);
        }

        netdev_dbg(dev->net,
                "Sending package with length %i and padding %i. Header: %6phC.",
                content_len, padlen, header_start);

        return skb;
}

static int
kalmia_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
{
        /*
         * Our task here is to strip off framing, leaving skb with one
         * data frame for the usbnet framework code to process.
         */
        static const u8 HEADER_END_OF_USB_PACKET[] =
                { 0x57, 0x5a, 0x00, 0x00, 0x08, 0x00 };
        static const u8 EXPECTED_UNKNOWN_HEADER_1[] =
                { 0x57, 0x43, 0x1e, 0x00, 0x15, 0x02 };
        static const u8 EXPECTED_UNKNOWN_HEADER_2[] =
                { 0x57, 0x50, 0x0e, 0x00, 0x00, 0x00 };
        int i = 0;

        /* incomplete header? */
        if (skb->len < KALMIA_HEADER_LENGTH)
                return 0;

        do {
                struct sk_buff *skb2 = NULL;
                u8 *header_start;
                u16 usb_packet_length, ether_packet_length;
                int is_last;

                header_start = skb->data;

                if (unlikely(header_start[0] != 0x57 || header_start[1] != 0x44)) {
                        if (!memcmp(header_start, EXPECTED_UNKNOWN_HEADER_1,
                                sizeof(EXPECTED_UNKNOWN_HEADER_1)) || !memcmp(
                                header_start, EXPECTED_UNKNOWN_HEADER_2,
                                sizeof(EXPECTED_UNKNOWN_HEADER_2))) {
                                netdev_dbg(dev->net,
                                        "Received expected unknown frame header: %6phC. Package length: %i\n",
                                        header_start,
                                        skb->len - KALMIA_HEADER_LENGTH);
                        }
                        else {
                                netdev_err(dev->net,
                                        "Received unknown frame header: %6phC. Package length: %i\n",
                                        header_start,
                                        skb->len - KALMIA_HEADER_LENGTH);
                                return 0;
                        }
                }
                else
                        netdev_dbg(dev->net,
                                "Received header: %6phC. Package length: %i\n",
                                header_start, skb->len - KALMIA_HEADER_LENGTH);

                /* subtract start header and end header */
                usb_packet_length = skb->len - (2 * KALMIA_HEADER_LENGTH);
                ether_packet_length = get_unaligned_le16(&header_start[2]);
                skb_pull(skb, KALMIA_HEADER_LENGTH);

                /* Some small packets misses end marker */
                if (usb_packet_length < ether_packet_length) {
                        ether_packet_length = usb_packet_length
                                + KALMIA_HEADER_LENGTH;
                        is_last = true;
                }
                else {
                        netdev_dbg(dev->net, "Correct package length #%i", i
                                + 1);

                        is_last = (memcmp(skb->data + ether_packet_length,
                                HEADER_END_OF_USB_PACKET,
                                sizeof(HEADER_END_OF_USB_PACKET)) == 0);
                        if (!is_last) {
                                header_start = skb->data + ether_packet_length;
                                netdev_dbg(dev->net,
                                        "End header: %6phC. Package length: %i\n",
                                        header_start,
                                        skb->len - KALMIA_HEADER_LENGTH);
                        }
                }

                if (is_last) {
                        skb2 = skb;
                }
                else {
                        skb2 = skb_clone(skb, GFP_ATOMIC);
                        if (unlikely(!skb2))
                                return 0;
                }

                skb_trim(skb2, ether_packet_length);

                if (is_last) {
                        return 1;
                }
                else {
                        usbnet_skb_return(dev, skb2);
                        skb_pull(skb, ether_packet_length);
                }

                i++;
        }
        while (skb->len);

        return 1;
}

static const struct driver_info kalmia_info = {
        .description = "Samsung Kalmia LTE USB dongle",
        .flags = FLAG_WWAN,
        .bind = kalmia_bind,
        .rx_fixup = kalmia_rx_fixup,
        .tx_fixup = kalmia_tx_fixup
};

/*-------------------------------------------------------------------------*/

static const struct usb_device_id products[] = {
        /* The unswitched USB ID, to get the module auto loaded: */
        { USB_DEVICE(0x04e8, 0x689a) },
        /* The stick switched into modem (by e.g. usb_modeswitch): */
        { USB_DEVICE(0x04e8, 0x6889),
                .driver_info = (unsigned long) &kalmia_info, },
        { /* EMPTY == end of list */} };
MODULE_DEVICE_TABLE( usb, products);

static struct usb_driver kalmia_driver = {
        .name = "kalmia",
        .id_table = products,
        .probe = usbnet_probe,
        .disconnect = usbnet_disconnect,
        .suspend = usbnet_suspend,
        .resume = usbnet_resume,
        .disable_hub_initiated_lpm = 1,
};

module_usb_driver(kalmia_driver);

MODULE_AUTHOR("Marius Bjoernstad Kotsbak <marius@kotsbak.com>");
MODULE_DESCRIPTION("Samsung Kalmia USB network driver");
MODULE_LICENSE("GPL");