// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * GeneSys GL620USB-A based links
 * Copyright (C) 2001 by Jiun-Jie Huang <huangjj@genesyslogic.com.tw>
 * Copyright (C) 2001 by Stanislav Brabec <utx@penguin.cz>
 */

// #define      DEBUG                   // error path messages, extra info
// #define      VERBOSE                 // more; success messages

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


/*
 * GeneSys GL620USB-A (www.genesyslogic.com.tw)
 *
 * ... should partially interop with the Win32 driver for this hardware.
 * The GeneSys docs imply there's some NDIS issue motivating this framing.
 *
 * Some info from GeneSys:
 *  - GL620USB-A is full duplex; GL620USB is only half duplex for bulk.
 *    (Some cables, like the BAFO-100c, use the half duplex version.)
 *  - For the full duplex model, the low bit of the version code says
 *    which side is which ("left/right").
 *  - For the half duplex type, a control/interrupt handshake settles
 *    the transfer direction.  (That's disabled here, partially coded.)
 *    A control URB would block until other side writes an interrupt.
 *
 * Original code from Jiun-Jie Huang <huangjj@genesyslogic.com.tw>
 * and merged into "usbnet" by Stanislav Brabec <utx@penguin.cz>.
 */

// control msg write command
#define GENELINK_CONNECT_WRITE                  0xF0
// interrupt pipe index
#define GENELINK_INTERRUPT_PIPE                 0x03
// interrupt read buffer size
#define INTERRUPT_BUFSIZE                       0x08
// interrupt pipe interval value
#define GENELINK_INTERRUPT_INTERVAL             0x10
// max transmit packet number per transmit
#define GL_MAX_TRANSMIT_PACKETS                 32
// max packet length
#define GL_MAX_PACKET_LEN                       1514
// max receive buffer size
#define GL_RCV_BUF_SIZE         \
        (((GL_MAX_PACKET_LEN + 4) * GL_MAX_TRANSMIT_PACKETS) + 4)

struct gl_packet {
        __le32          packet_length;
        char            packet_data[];
};

struct gl_header {
        __le32                  packet_count;
        struct gl_packet        packets;
};

static int genelink_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
{
        struct gl_header        *header;
        struct gl_packet        *packet;
        struct sk_buff          *gl_skb;
        u32                     size;
        u32                     count;

        /* This check is no longer done by usbnet */
        if (skb->len < dev->net->hard_header_len)
                return 0;

        header = (struct gl_header *) skb->data;

        // get the packet count of the received skb
        count = le32_to_cpu(header->packet_count);
        if (count > GL_MAX_TRANSMIT_PACKETS) {
                netdev_dbg(dev->net,
                           "genelink: invalid received packet count %u\n",
                           count);
                return 0;
        }

        // set the current packet pointer to the first packet
        packet = &header->packets;

        // decrement the length for the packet count size 4 bytes
        skb_pull(skb, 4);

        while (count > 1) {
                // get the packet length
                size = le32_to_cpu(packet->packet_length);

                // this may be a broken packet
                if (size > GL_MAX_PACKET_LEN) {
                        netdev_dbg(dev->net, "genelink: invalid rx length %d\n",
                                   size);
                        return 0;
                }

                // allocate the skb for the individual packet
                gl_skb = alloc_skb(size, GFP_ATOMIC);
                if (gl_skb) {

                        // copy the packet data to the new skb
                        skb_put_data(gl_skb, packet->packet_data, size);
                        usbnet_skb_return(dev, gl_skb);
                }

                // advance to the next packet
                packet = (struct gl_packet *)&packet->packet_data[size];
                count--;

                // shift the data pointer to the next gl_packet
                skb_pull(skb, size + 4);
        }

        // skip the packet length field 4 bytes
        skb_pull(skb, 4);

        if (skb->len > GL_MAX_PACKET_LEN) {
                netdev_dbg(dev->net, "genelink: invalid rx length %d\n",
                           skb->len);
                return 0;
        }
        return 1;
}

static struct sk_buff *
genelink_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
{
        int     padlen;
        int     length = skb->len;
        int     headroom = skb_headroom(skb);
        int     tailroom = skb_tailroom(skb);
        __le32  *packet_count;
        __le32  *packet_len;

        // FIXME:  magic numbers, bleech
        padlen = ((skb->len + (4 + 4*1)) % 64) ? 0 : 1;

        if ((!skb_cloned(skb))
                        && ((headroom + tailroom) >= (padlen + (4 + 4*1)))) {
                if ((headroom < (4 + 4*1)) || (tailroom < padlen)) {
                        skb->data = memmove(skb->head + (4 + 4*1),
                                             skb->data, skb->len);
                        skb_set_tail_pointer(skb, skb->len);
                }
        } else {
                struct sk_buff  *skb2;
                skb2 = skb_copy_expand(skb, (4 + 4*1) , padlen, flags);
                dev_kfree_skb_any(skb);
                skb = skb2;
                if (!skb)
                        return NULL;
        }

        // attach the packet count to the header
        packet_count = skb_push(skb, (4 + 4 * 1));
        packet_len = packet_count + 1;

        *packet_count = cpu_to_le32(1);
        *packet_len = cpu_to_le32(length);

        // add padding byte
        if ((skb->len % dev->maxpacket) == 0)
                skb_put(skb, 1);

        return skb;
}

static int genelink_bind(struct usbnet *dev, struct usb_interface *intf)
{
        dev->hard_mtu = GL_RCV_BUF_SIZE;
        dev->net->hard_header_len += 4;
        return usbnet_get_endpoints(dev, intf);
}

static const struct driver_info genelink_info = {
        .description =  "Genesys GeneLink",
        .flags =        FLAG_POINTTOPOINT | FLAG_FRAMING_GL | FLAG_NO_SETINT,
        .bind =         genelink_bind,
        .rx_fixup =     genelink_rx_fixup,
        .tx_fixup =     genelink_tx_fixup,

        .in = 1, .out = 2,

#ifdef  GENELINK_ACK
        .check_connect =genelink_check_connect,
#endif
};

static const struct usb_device_id       products [] = {

{
        USB_DEVICE(0x05e3, 0x0502),     // GL620USB-A
        .driver_info =  (unsigned long) &genelink_info,
},
        /* NOT: USB_DEVICE(0x05e3, 0x0501),     // GL620USB
         * that's half duplex, not currently supported
         */
        { },            // END
};
MODULE_DEVICE_TABLE(usb, products);

static struct usb_driver gl620a_driver = {
        .name =         "gl620a",
        .id_table =     products,
        .probe =        usbnet_probe,
        .disconnect =   usbnet_disconnect,
        .suspend =      usbnet_suspend,
        .resume =       usbnet_resume,
        .disable_hub_initiated_lpm = 1,
};

module_usb_driver(gl620a_driver);

MODULE_AUTHOR("Jiun-Jie Huang");
MODULE_DESCRIPTION("GL620-USB-A Host-to-Host Link cables");
MODULE_LICENSE("GPL");