// 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;
	dev->in = usb_rcvbulkpipe(dev->udev, dev->driver_info->in);
	dev->out = usb_sndbulkpipe(dev->udev, dev->driver_info->out);
	return 0;
}

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");