/* znet.c: An Zenith Z-Note ethernet driver for linux. */

/*
        Written by Donald Becker.

        The author may be reached as becker@scyld.com.
        This driver is based on the Linux skeleton driver.  The copyright of the
        skeleton driver is held by the United States Government, as represented
        by DIRNSA, and it is released under the GPL.

        Thanks to Mike Hollick for alpha testing and suggestions.

  References:
           The Crynwr packet driver.

          "82593 CSMA/CD Core LAN Controller" Intel datasheet, 1992
          Intel Microcommunications Databook, Vol. 1, 1990.
    As usual with Intel, the documentation is incomplete and inaccurate.
        I had to read the Crynwr packet driver to figure out how to actually
        use the i82593, and guess at what register bits matched the loosely
        related i82586.

                                        Theory of Operation

        The i82593 used in the Zenith Z-Note series operates using two(!) slave
        DMA     channels, one interrupt, and one 8-bit I/O port.

        While there     several ways to configure '593 DMA system, I chose the one
        that seemed commensurate with the highest system performance in the face
        of moderate interrupt latency: Both DMA channels are configured as
        recirculating ring buffers, with one channel (#0) dedicated to Rx and
        the other channel (#1) to Tx and configuration.  (Note that this is
        different than the Crynwr driver, where the Tx DMA channel is initialized
        before each operation.  That approach simplifies operation and Tx error
        recovery, but requires additional I/O in normal operation and precludes
        transmit buffer chaining.)

        Both rings are set to 8192 bytes using {TX,RX}_RING_SIZE.  This provides
        a reasonable ring size for Rx, while simplifying DMA buffer allocation --
        DMA buffers must not cross a 128K boundary.  (In truth the size selection
        was influenced by my lack of '593 documentation.  I thus was constrained
        to use the Crynwr '593 initialization table, which sets the Rx ring size
        to 8K.)

        Despite my usual low opinion about Intel-designed parts, I must admit
        that the bulk data handling of the i82593 is a good design for
        an integrated system, like a laptop, where using two slave DMA channels
        doesn't pose a problem.  I still take issue with using only a single I/O
        port.  In the same controlled environment there are essentially no
        limitations on I/O space, and using multiple locations would eliminate
        the     need for multiple operations when looking at status registers,
        setting the Rx ring boundary, or switching to promiscuous mode.

        I also question Zenith's selection of the '593: one of the advertised
        advantages of earlier Intel parts was that if you figured out the magic
        initialization incantation you could use the same part on many different
        network types.  Zenith's use of the "FriendlyNet" (sic) connector rather
        than an on-board transceiver leads me to believe that they were planning
        to take advantage of this.  But, uhmmm, the '593 omits all but ethernet
        functionality from the serial subsystem.
 */

/* 10/2002

   o Resurected for Linux 2.5+ by Marc Zyngier <maz@wild-wind.fr.eu.org> :

   - Removed strange DMA snooping in znet_sent_packet, which lead to
     TX buffer corruption on my laptop.
   - Use init_etherdev stuff.
   - Use kmalloc-ed DMA buffers.
   - Use as few global variables as possible.
   - Use proper resources management.
   - Use wireless/i82593.h as much as possible (structure, constants)
   - Compiles as module or build-in.
   - Now survives unplugging/replugging cable.

   Some code was taken from wavelan_cs.

   Tested on a vintage Zenith Z-Note 433Lnp+. Probably broken on
   anything else. Testers (and detailed bug reports) are welcome :-).

   o TODO :

   - Properly handle multicast
   - Understand why some traffic patterns add a 1s latency...
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/ioport.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/if_arp.h>
#include <linux/bitops.h>

#include <asm/system.h>
#include <asm/io.h>
#include <asm/dma.h>

/* This include could be elsewhere, since it is not wireless specific */
#include "wireless/i82593.h"

static char version[] __initdata = "znet.c:v1.02 9/23/94 becker@scyld.com\n";

#ifndef ZNET_DEBUG
#define ZNET_DEBUG 1
#endif
static unsigned int znet_debug = ZNET_DEBUG;
module_param (znet_debug, int, 0);
MODULE_PARM_DESC (znet_debug, "ZNet debug level");
MODULE_LICENSE("GPL");

/* The DMA modes we need aren't in <dma.h>. */
#define DMA_RX_MODE             0x14    /* Auto init, I/O to mem, ++, demand. */
#define DMA_TX_MODE             0x18    /* Auto init, Mem to I/O, ++, demand. */
#define dma_page_eq(ptr1, ptr2) ((long)(ptr1)>>17 == (long)(ptr2)>>17)
#define RX_BUF_SIZE 8192
#define TX_BUF_SIZE 8192
#define DMA_BUF_SIZE (RX_BUF_SIZE + 16) /* 8k + 16 bytes for trailers */

#define TX_TIMEOUT      10

struct znet_private {
        int rx_dma, tx_dma;
        spinlock_t lock;
        short sia_base, sia_size, io_size;
        struct i82593_conf_block i593_init;
        /* The starting, current, and end pointers for the packet buffers. */
        ushort *rx_start, *rx_cur, *rx_end;
        ushort *tx_start, *tx_cur, *tx_end;
        ushort tx_buf_len;                      /* Tx buffer length, in words. */
};

/* Only one can be built-in;-> */
static struct net_device *znet_dev;

struct netidblk {
        char magic[8];          /* The magic number (string) "NETIDBLK" */
        unsigned char netid[8]; /* The physical station address */
        char nettype, globalopt;
        char vendor[8];         /* The machine vendor and product name. */
        char product[8];
        char irq1, irq2;                /* Interrupts, only one is currently used.      */
        char dma1, dma2;
        short dma_mem_misc[8];          /* DMA buffer locations (unused in Linux). */
        short iobase1, iosize1;
        short iobase2, iosize2;         /* Second iobase unused. */
        char driver_options;                    /* Misc. bits */
        char pad;
};

static int      znet_open(struct net_device *dev);
static int      znet_send_packet(struct sk_buff *skb, struct net_device *dev);
static irqreturn_t znet_interrupt(int irq, void *dev_id);
static void     znet_rx(struct net_device *dev);
static int      znet_close(struct net_device *dev);
static void hardware_init(struct net_device *dev);
static void update_stop_hit(short ioaddr, unsigned short rx_stop_offset);
static void znet_tx_timeout (struct net_device *dev);

/* Request needed resources */
static int znet_request_resources (struct net_device *dev)
{
        struct znet_private *znet = dev->priv;
        unsigned long flags;

        if (request_irq (dev->irq, &znet_interrupt, 0, "ZNet", dev))
                goto failed;
        if (request_dma (znet->rx_dma, "ZNet rx"))
                goto free_irq;
        if (request_dma (znet->tx_dma, "ZNet tx"))
                goto free_rx_dma;
        if (!request_region (znet->sia_base, znet->sia_size, "ZNet SIA"))
                goto free_tx_dma;
        if (!request_region (dev->base_addr, znet->io_size, "ZNet I/O"))
                goto free_sia;

        return 0;                               /* Happy ! */

 free_sia:
        release_region (znet->sia_base, znet->sia_size);
 free_tx_dma:
        flags = claim_dma_lock();
        free_dma (znet->tx_dma);
        release_dma_lock (flags);
 free_rx_dma:
        flags = claim_dma_lock();
        free_dma (znet->rx_dma);
        release_dma_lock (flags);
 free_irq:
        free_irq (dev->irq, dev);
 failed:
        return -1;
}

static void znet_release_resources (struct net_device *dev)
{
        struct znet_private *znet = dev->priv;
        unsigned long flags;

        release_region (znet->sia_base, znet->sia_size);
        release_region (dev->base_addr, znet->io_size);
        flags = claim_dma_lock();
        free_dma (znet->tx_dma);
        free_dma (znet->rx_dma);
        release_dma_lock (flags);
        free_irq (dev->irq, dev);
}

/* Keep the magical SIA stuff in a single function... */
static void znet_transceiver_power (struct net_device *dev, int on)
{
        struct znet_private *znet = dev->priv;
        unsigned char v;

        /* Turn on/off the 82501 SIA, using zenith-specific magic. */
        /* Select LAN control register */
        outb(0x10, znet->sia_base);

        if (on)
                v = inb(znet->sia_base + 1) | 0x84;
        else
                v = inb(znet->sia_base + 1) & ~0x84;

        outb(v, znet->sia_base+1); /* Turn on/off LAN power (bit 2). */
}

/* Init the i82593, with current promisc/mcast configuration.
   Also used from hardware_init. */
static void znet_set_multicast_list (struct net_device *dev)
{
        struct znet_private *znet = dev->priv;
        short ioaddr = dev->base_addr;
        struct i82593_conf_block *cfblk = &znet->i593_init;

        memset(cfblk, 0x00, sizeof(struct i82593_conf_block));

        /* The configuration block.  What an undocumented nightmare.
           The first set of values are those suggested (without explanation)
           for ethernet in the Intel 82586 databook.  The rest appear to be
           completely undocumented, except for cryptic notes in the Crynwr
           packet driver.  This driver uses the Crynwr values verbatim. */

        /* maz : Rewritten to take advantage of the wanvelan includes.
           At least we have names, not just blind values */

        /* Byte 0 */
        cfblk->fifo_limit = 10; /* = 16 B rx and 80 B tx fifo thresholds */
        cfblk->forgnesi = 0;    /* 0=82C501, 1=AMD7992B compatibility */
        cfblk->fifo_32 = 1;
        cfblk->d6mod = 0;       /* Run in i82593 advanced mode */
        cfblk->throttle_enb = 1;

        /* Byte 1 */
        cfblk->throttle = 8;    /* Continuous w/interrupts, 128-clock DMA. */
        cfblk->cntrxint = 0;    /* enable continuous mode receive interrupts */
        cfblk->contin = 1;      /* enable continuous mode */

        /* Byte 2 */
        cfblk->addr_len = ETH_ALEN;
        cfblk->acloc = 1;       /* Disable source addr insertion by i82593 */
        cfblk->preamb_len = 2;  /* 8 bytes preamble */
        cfblk->loopback = 0;    /* Loopback off */

        /* Byte 3 */
        cfblk->lin_prio = 0;    /* Default priorities & backoff methods. */
        cfblk->tbofstop = 0;
        cfblk->exp_prio = 0;
        cfblk->bof_met = 0;

        /* Byte 4 */
        cfblk->ifrm_spc = 6;    /* 96 bit times interframe spacing */

        /* Byte 5 */
        cfblk->slottim_low = 0; /* 512 bit times slot time (low) */

        /* Byte 6 */
        cfblk->slottim_hi = 2;  /* 512 bit times slot time (high) */
        cfblk->max_retr = 15;   /* 15 collisions retries */

        /* Byte 7 */
        cfblk->prmisc = ((dev->flags & IFF_PROMISC) ? 1 : 0); /* Promiscuous mode */
        cfblk->bc_dis = 0;      /* Enable broadcast reception */
        cfblk->crs_1 = 0;       /* Don't transmit without carrier sense */
        cfblk->nocrc_ins = 0;   /* i82593 generates CRC */
        cfblk->crc_1632 = 0;    /* 32-bit Autodin-II CRC */
        cfblk->crs_cdt = 0;     /* CD not to be interpreted as CS */

        /* Byte 8 */
        cfblk->cs_filter = 0;   /* CS is recognized immediately */
        cfblk->crs_src = 0;     /* External carrier sense */
        cfblk->cd_filter = 0;   /* CD is recognized immediately */

        /* Byte 9 */
        cfblk->min_fr_len = ETH_ZLEN >> 2; /* Minimum frame length */

        /* Byte A */
        cfblk->lng_typ = 1;     /* Type/length checks OFF */
        cfblk->lng_fld = 1;     /* Disable 802.3 length field check */
        cfblk->rxcrc_xf = 1;    /* Don't transfer CRC to memory */
        cfblk->artx = 1;        /* Disable automatic retransmission */
        cfblk->sarec = 1;       /* Disable source addr trig of CD */
        cfblk->tx_jabber = 0;   /* Disable jabber jam sequence */
        cfblk->hash_1 = 1;      /* Use bits 0-5 in mc address hash */
        cfblk->lbpkpol = 0;     /* Loopback pin active high */

        /* Byte B */
        cfblk->fdx = 0;         /* Disable full duplex operation */

        /* Byte C */
        cfblk->dummy_6 = 0x3f;  /* all ones, Default multicast addresses & backoff. */
        cfblk->mult_ia = 0;     /* No multiple individual addresses */
        cfblk->dis_bof = 0;     /* Disable the backoff algorithm ?! */

        /* Byte D */
        cfblk->dummy_1 = 1;     /* set to 1 */
        cfblk->tx_ifs_retrig = 3; /* Hmm... Disabled */
        cfblk->mc_all = (dev->mc_list || (dev->flags&IFF_ALLMULTI));/* multicast all mode */
        cfblk->rcv_mon = 0;     /* Monitor mode disabled */
        cfblk->frag_acpt = 0;   /* Do not accept fragments */
        cfblk->tstrttrs = 0;    /* No start transmission threshold */

        /* Byte E */
        cfblk->fretx = 1;       /* FIFO automatic retransmission */
        cfblk->runt_eop = 0;    /* drop "runt" packets */
        cfblk->hw_sw_pin = 0;   /* ?? */
        cfblk->big_endn = 0;    /* Big Endian ? no... */
        cfblk->syncrqs = 1;     /* Synchronous DRQ deassertion... */
        cfblk->sttlen = 1;      /* 6 byte status registers */
        cfblk->rx_eop = 0;      /* Signal EOP on packet reception */
        cfblk->tx_eop = 0;      /* Signal EOP on packet transmission */

        /* Byte F */
        cfblk->rbuf_size = RX_BUF_SIZE >> 12; /* Set receive buffer size */
        cfblk->rcvstop = 1;     /* Enable Receive Stop Register */

        if (znet_debug > 2) {
                int i;
                unsigned char *c;

                for (i = 0, c = (char *) cfblk; i < sizeof (*cfblk); i++)
                        printk ("%02X ", c[i]);
                printk ("\n");
        }

        *znet->tx_cur++ = sizeof(struct i82593_conf_block);
        memcpy(znet->tx_cur, cfblk, sizeof(struct i82593_conf_block));
        znet->tx_cur += sizeof(struct i82593_conf_block)/2;
        outb(OP0_CONFIGURE | CR0_CHNL, ioaddr);

        /* XXX FIXME maz : Add multicast addresses here, so having a
         * multicast address configured isn't equal to IFF_ALLMULTI */
}

/* The Z-Note probe is pretty easy.  The NETIDBLK exists in the safe-to-probe
   BIOS area.  We just scan for the signature, and pull the vital parameters
   out of the structure. */

static int __init znet_probe (void)
{
        int i;
        struct netidblk *netinfo;
        struct znet_private *znet;
        struct net_device *dev;
        char *p;
        int err = -ENOMEM;
        DECLARE_MAC_BUF(mac);

        /* This code scans the region 0xf0000 to 0xfffff for a "NETIDBLK". */
        for(p = (char *)phys_to_virt(0xf0000); p < (char *)phys_to_virt(0x100000); p++)
                if (*p == 'N'  &&  strncmp(p, "NETIDBLK", 8) == 0)
                        break;

        if (p >= (char *)phys_to_virt(0x100000)) {
                if (znet_debug > 1)
                        printk(KERN_INFO "No Z-Note ethernet adaptor found.\n");
                return -ENODEV;
        }

        dev = alloc_etherdev(sizeof(struct znet_private));
        if (!dev)
                return -ENOMEM;

        znet = dev->priv;

        netinfo = (struct netidblk *)p;
        dev->base_addr = netinfo->iobase1;
        dev->irq = netinfo->irq1;

        /* The station address is in the "netidblk" at 0x0f0000. */
        for (i = 0; i < 6; i++)
                dev->dev_addr[i] = netinfo->netid[i];

        printk(KERN_INFO "%s: ZNET at %#3lx, %s"
               ", using IRQ %d DMA %d and %d.\n",
               dev->name, dev->base_addr, print_mac(mac, dev->dev_addr),
               dev->irq, netinfo->dma1, netinfo->dma2);

        if (znet_debug > 1) {
                printk(KERN_INFO "%s: vendor '%16.16s' IRQ1 %d IRQ2 %d DMA1 %d DMA2 %d.\n",
                       dev->name, netinfo->vendor,
                       netinfo->irq1, netinfo->irq2,
                       netinfo->dma1, netinfo->dma2);
                printk(KERN_INFO "%s: iobase1 %#x size %d iobase2 %#x size %d net type %2.2x.\n",
                       dev->name, netinfo->iobase1, netinfo->iosize1,
                       netinfo->iobase2, netinfo->iosize2, netinfo->nettype);
        }

        if (znet_debug > 0)
                printk(KERN_INFO "%s", version);

        znet->rx_dma = netinfo->dma1;
        znet->tx_dma = netinfo->dma2;
        spin_lock_init(&znet->lock);
        znet->sia_base = 0xe6;  /* Magic address for the 82501 SIA */
        znet->sia_size = 2;
        /* maz: Despite the '593 being advertised above as using a
         * single 8bits I/O port, this driver does many 16bits
         * access. So set io_size accordingly */
        znet->io_size  = 2;

        if (!(znet->rx_start = kmalloc (DMA_BUF_SIZE, GFP_KERNEL | GFP_DMA)))
                goto free_dev;
        if (!(znet->tx_start = kmalloc (DMA_BUF_SIZE, GFP_KERNEL | GFP_DMA)))
                goto free_rx;

        if (!dma_page_eq (znet->rx_start, znet->rx_start + (RX_BUF_SIZE/2-1)) ||
            !dma_page_eq (znet->tx_start, znet->tx_start + (TX_BUF_SIZE/2-1))) {
                printk (KERN_WARNING "tx/rx crossing DMA frontiers, giving up\n");
                goto free_tx;
        }

        znet->rx_end = znet->rx_start + RX_BUF_SIZE/2;
        znet->tx_buf_len = TX_BUF_SIZE/2;
        znet->tx_end = znet->tx_start + znet->tx_buf_len;

        /* The ZNET-specific entries in the device structure. */
        dev->open = &znet_open;
        dev->hard_start_xmit = &znet_send_packet;
        dev->stop = &znet_close;
        dev->set_multicast_list = &znet_set_multicast_list;
        dev->tx_timeout = znet_tx_timeout;
        dev->watchdog_timeo = TX_TIMEOUT;
        err = register_netdev(dev);
        if (err)
                goto free_tx;
        znet_dev = dev;
        return 0;

 free_tx:
        kfree(znet->tx_start);
 free_rx:
        kfree(znet->rx_start);
 free_dev:
        free_netdev(dev);
        return err;
}


static int znet_open(struct net_device *dev)
{
        int ioaddr = dev->base_addr;

        if (znet_debug > 2)
                printk(KERN_DEBUG "%s: znet_open() called.\n", dev->name);

        /* These should never fail.  You can't add devices to a sealed box! */
        if (znet_request_resources (dev)) {
                printk(KERN_WARNING "%s: Not opened -- resource busy?!?\n", dev->name);
                return -EBUSY;
        }

        znet_transceiver_power (dev, 1);

        /* According to the Crynwr driver we should wait 50 msec. for the
           LAN clock to stabilize.  My experiments indicates that the '593 can
           be initialized immediately.  The delay is probably needed for the
           DC-to-DC converter to come up to full voltage, and for the oscillator
           to be spot-on at 20Mhz before transmitting.
           Until this proves to be a problem we rely on the higher layers for the
           delay and save allocating a timer entry. */

        /* maz : Well, I'm getting every time the following message
         * without the delay on a 486@33. This machine is much too
         * fast... :-) So maybe the Crynwr driver wasn't wrong after
         * all, even if the message is completly harmless on my
         * setup. */
        mdelay (50);

        /* This follows the packet driver's lead, and checks for success. */
        if (inb(ioaddr) != 0x10 && inb(ioaddr) != 0x00)
                printk(KERN_WARNING "%s: Problem turning on the transceiver power.\n",
                       dev->name);

        hardware_init(dev);
        netif_start_queue (dev);

        return 0;
}


static void znet_tx_timeout (struct net_device *dev)
{
        int ioaddr = dev->base_addr;
        ushort event, tx_status, rx_offset, state;

        outb (CR0_STATUS_0, ioaddr);
        event = inb (ioaddr);
        outb (CR0_STATUS_1, ioaddr);
        tx_status = inw (ioaddr);
        outb (CR0_STATUS_2, ioaddr);
        rx_offset = inw (ioaddr);
        outb (CR0_STATUS_3, ioaddr);
        state = inb (ioaddr);
        printk (KERN_WARNING "%s: transmit timed out, status %02x %04x %04x %02x,"
         " resetting.\n", dev->name, event, tx_status, rx_offset, state);
        if (tx_status == TX_LOST_CRS)
                printk (KERN_WARNING "%s: Tx carrier error, check transceiver cable.\n",
                        dev->name);
        outb (OP0_RESET, ioaddr);
        hardware_init (dev);
        netif_wake_queue (dev);
}

static int znet_send_packet(struct sk_buff *skb, struct net_device *dev)
{
        int ioaddr = dev->base_addr;
        struct znet_private *znet = dev->priv;
        unsigned long flags;
        short length = skb->len;

        if (znet_debug > 4)
                printk(KERN_DEBUG "%s: ZNet_send_packet.\n", dev->name);

        if (length < ETH_ZLEN) {
                if (skb_padto(skb, ETH_ZLEN))
                        return 0;
                length = ETH_ZLEN;
        }

        netif_stop_queue (dev);

        /* Check that the part hasn't reset itself, probably from suspend. */
        outb(CR0_STATUS_0, ioaddr);
        if (inw(ioaddr) == 0x0010 &&
            inw(ioaddr) == 0x0000 &&
            inw(ioaddr) == 0x0010) {
                if (znet_debug > 1)
                        printk (KERN_WARNING "%s : waking up\n", dev->name);
                hardware_init(dev);
                znet_transceiver_power (dev, 1);
        }

        if (1) {
                unsigned char *buf = (void *)skb->data;
                ushort *tx_link = znet->tx_cur - 1;
                ushort rnd_len = (length + 1)>>1;

                dev->stats.tx_bytes+=length;

                if (znet->tx_cur >= znet->tx_end)
                  znet->tx_cur = znet->tx_start;
                *znet->tx_cur++ = length;
                if (znet->tx_cur + rnd_len + 1 > znet->tx_end) {
                        int semi_cnt = (znet->tx_end - znet->tx_cur)<<1; /* Cvrt to byte cnt. */
                        memcpy(znet->tx_cur, buf, semi_cnt);
                        rnd_len -= semi_cnt>>1;
                        memcpy(znet->tx_start, buf + semi_cnt, length - semi_cnt);
                        znet->tx_cur = znet->tx_start + rnd_len;
                } else {
                        memcpy(znet->tx_cur, buf, skb->len);
                        znet->tx_cur += rnd_len;
                }
                *znet->tx_cur++ = 0;

                spin_lock_irqsave(&znet->lock, flags);
                {
                        *tx_link = OP0_TRANSMIT | CR0_CHNL;
                        /* Is this always safe to do? */
                        outb(OP0_TRANSMIT | CR0_CHNL, ioaddr);
                }
                spin_unlock_irqrestore (&znet->lock, flags);

                dev->trans_start = jiffies;
                netif_start_queue (dev);

                if (znet_debug > 4)
                  printk(KERN_DEBUG "%s: Transmitter queued, length %d.\n", dev->name, length);
        }
        dev_kfree_skb(skb);
        return 0;
}

/* The ZNET interrupt handler. */
static irqreturn_t znet_interrupt(int irq, void *dev_id)
{
        struct net_device *dev = dev_id;
        struct znet_private *znet = dev->priv;
        int ioaddr;
        int boguscnt = 20;
        int handled = 0;

        spin_lock (&znet->lock);

        ioaddr = dev->base_addr;

        outb(CR0_STATUS_0, ioaddr);
        do {
                ushort status = inb(ioaddr);
                if (znet_debug > 5) {
                        ushort result, rx_ptr, running;
                        outb(CR0_STATUS_1, ioaddr);
                        result = inw(ioaddr);
                        outb(CR0_STATUS_2, ioaddr);
                        rx_ptr = inw(ioaddr);
                        outb(CR0_STATUS_3, ioaddr);
                        running = inb(ioaddr);
                        printk(KERN_DEBUG "%s: interrupt, status %02x, %04x %04x %02x serial %d.\n",
                                 dev->name, status, result, rx_ptr, running, boguscnt);
                }
                if ((status & SR0_INTERRUPT) == 0)
                        break;

                handled = 1;

                if ((status & SR0_EVENT_MASK) == SR0_TRANSMIT_DONE ||
                    (status & SR0_EVENT_MASK) == SR0_RETRANSMIT_DONE ||
                    (status & SR0_EVENT_MASK) == SR0_TRANSMIT_NO_CRC_DONE) {
                        int tx_status;
                        outb(CR0_STATUS_1, ioaddr);
                        tx_status = inw(ioaddr);
                        /* It's undocumented, but tx_status seems to match the i82586. */
                        if (tx_status & TX_OK) {
                                dev->stats.tx_packets++;
                                dev->stats.collisions += tx_status & TX_NCOL_MASK;
                        } else {
                                if (tx_status & (TX_LOST_CTS | TX_LOST_CRS))
                                        dev->stats.tx_carrier_errors++;
                                if (tx_status & TX_UND_RUN)
                                        dev->stats.tx_fifo_errors++;
                                if (!(tx_status & TX_HRT_BEAT))
                                        dev->stats.tx_heartbeat_errors++;
                                if (tx_status & TX_MAX_COL)
                                        dev->stats.tx_aborted_errors++;
                                /* ...and the catch-all. */
                                if ((tx_status | (TX_LOST_CRS | TX_LOST_CTS | TX_UND_RUN | TX_HRT_BEAT | TX_MAX_COL)) != (TX_LOST_CRS | TX_LOST_CTS | TX_UND_RUN | TX_HRT_BEAT | TX_MAX_COL))
                                        dev->stats.tx_errors++;

                                /* Transceiver may be stuck if cable
                                 * was removed while emiting a
                                 * packet. Flip it off, then on to
                                 * reset it. This is very empirical,
                                 * but it seems to work. */

                                znet_transceiver_power (dev, 0);
                                znet_transceiver_power (dev, 1);
                        }
                        netif_wake_queue (dev);
                }

                if ((status & SR0_RECEPTION) ||
                    (status & SR0_EVENT_MASK) == SR0_STOP_REG_HIT) {
                        znet_rx(dev);
                }
                /* Clear the interrupts we've handled. */
                outb(CR0_INT_ACK, ioaddr);
        } while (boguscnt--);

        spin_unlock (&znet->lock);

        return IRQ_RETVAL(handled);
}

static void znet_rx(struct net_device *dev)
{
        struct znet_private *znet = dev->priv;
        int ioaddr = dev->base_addr;
        int boguscount = 1;
        short next_frame_end_offset = 0;                /* Offset of next frame start. */
        short *cur_frame_end;
        short cur_frame_end_offset;

        outb(CR0_STATUS_2, ioaddr);
        cur_frame_end_offset = inw(ioaddr);

        if (cur_frame_end_offset == znet->rx_cur - znet->rx_start) {
                printk(KERN_WARNING "%s: Interrupted, but nothing to receive, offset %03x.\n",
                           dev->name, cur_frame_end_offset);
                return;
        }

        /* Use same method as the Crynwr driver: construct a forward list in
           the same area of the backwards links we now have.  This allows us to
           pass packets to the upper layers in the order they were received --
           important for fast-path sequential operations. */
         while (znet->rx_start + cur_frame_end_offset != znet->rx_cur
                        && ++boguscount < 5) {
                unsigned short hi_cnt, lo_cnt, hi_status, lo_status;
                int count, status;

                if (cur_frame_end_offset < 4) {
                        /* Oh no, we have a special case: the frame trailer wraps around
                           the end of the ring buffer.  We've saved space at the end of
                           the ring buffer for just this problem. */
                        memcpy(znet->rx_end, znet->rx_start, 8);
                        cur_frame_end_offset += (RX_BUF_SIZE/2);
                }
                cur_frame_end = znet->rx_start + cur_frame_end_offset - 4;

                lo_status = *cur_frame_end++;
                hi_status = *cur_frame_end++;
                status = ((hi_status & 0xff) << 8) + (lo_status & 0xff);
                lo_cnt = *cur_frame_end++;
                hi_cnt = *cur_frame_end++;
                count = ((hi_cnt & 0xff) << 8) + (lo_cnt & 0xff);

                if (znet_debug > 5)
                  printk(KERN_DEBUG "Constructing trailer at location %03x, %04x %04x %04x %04x"
                                 " count %#x status %04x.\n",
                                 cur_frame_end_offset<<1, lo_status, hi_status, lo_cnt, hi_cnt,
                                 count, status);
                cur_frame_end[-4] = status;
                cur_frame_end[-3] = next_frame_end_offset;
                cur_frame_end[-2] = count;
                next_frame_end_offset = cur_frame_end_offset;
                cur_frame_end_offset -= ((count + 1)>>1) + 3;
                if (cur_frame_end_offset < 0)
                  cur_frame_end_offset += RX_BUF_SIZE/2;
        };

        /* Now step  forward through the list. */
        do {
                ushort *this_rfp_ptr = znet->rx_start + next_frame_end_offset;
                int status = this_rfp_ptr[-4];
                int pkt_len = this_rfp_ptr[-2];

                if (znet_debug > 5)
                  printk(KERN_DEBUG "Looking at trailer ending at %04x status %04x length %03x"
                                 " next %04x.\n", next_frame_end_offset<<1, status, pkt_len,
                                 this_rfp_ptr[-3]<<1);
                /* Once again we must assume that the i82586 docs apply. */
                if ( ! (status & RX_RCV_OK)) { /* There was an error. */
                        dev->stats.rx_errors++;
                        if (status & RX_CRC_ERR) dev->stats.rx_crc_errors++;
                        if (status & RX_ALG_ERR) dev->stats.rx_frame_errors++;
#if 0
                        if (status & 0x0200) dev->stats.rx_over_errors++; /* Wrong. */
                        if (status & 0x0100) dev->stats.rx_fifo_errors++;
#else
                        /* maz : Wild guess... */
                        if (status & RX_OVRRUN) dev->stats.rx_over_errors++;
#endif
                        if (status & RX_SRT_FRM) dev->stats.rx_length_errors++;
                } else if (pkt_len > 1536) {
                        dev->stats.rx_length_errors++;
                } else {
                        /* Malloc up new buffer. */
                        struct sk_buff *skb;

                        skb = dev_alloc_skb(pkt_len);
                        if (skb == NULL) {
                                if (znet_debug)
                                  printk(KERN_WARNING "%s: Memory squeeze, dropping packet.\n", dev->name);
                                dev->stats.rx_dropped++;
                                break;
                        }

                        if (&znet->rx_cur[(pkt_len+1)>>1] > znet->rx_end) {
                                int semi_cnt = (znet->rx_end - znet->rx_cur)<<1;
                                memcpy(skb_put(skb,semi_cnt), znet->rx_cur, semi_cnt);
                                memcpy(skb_put(skb,pkt_len-semi_cnt), znet->rx_start,
                                           pkt_len - semi_cnt);
                        } else {
                                memcpy(skb_put(skb,pkt_len), znet->rx_cur, pkt_len);
                                if (znet_debug > 6) {
                                        unsigned int *packet = (unsigned int *) skb->data;
                                        printk(KERN_DEBUG "Packet data is %08x %08x %08x %08x.\n", packet[0],
                                                   packet[1], packet[2], packet[3]);
                                }
                  }
                  skb->protocol=eth_type_trans(skb,dev);
                  netif_rx(skb);
                  dev->last_rx = jiffies;
                  dev->stats.rx_packets++;
                  dev->stats.rx_bytes += pkt_len;
                }
                znet->rx_cur = this_rfp_ptr;
                if (znet->rx_cur >= znet->rx_end)
                        znet->rx_cur -= RX_BUF_SIZE/2;
                update_stop_hit(ioaddr, (znet->rx_cur - znet->rx_start)<<1);
                next_frame_end_offset = this_rfp_ptr[-3];
                if (next_frame_end_offset == 0)         /* Read all the frames? */
                        break;                  /* Done for now */
                this_rfp_ptr = znet->rx_start + next_frame_end_offset;
        } while (--boguscount);

        /* If any worth-while packets have been received, dev_rint()
           has done a mark_bh(INET_BH) for us and will work on them
           when we get to the bottom-half routine. */
        return;
}

/* The inverse routine to znet_open(). */
static int znet_close(struct net_device *dev)
{
        int ioaddr = dev->base_addr;

        netif_stop_queue (dev);

        outb(OP0_RESET, ioaddr);                        /* CMD0_RESET */

        if (znet_debug > 1)
                printk(KERN_DEBUG "%s: Shutting down ethercard.\n", dev->name);
        /* Turn off transceiver power. */
        znet_transceiver_power (dev, 0);

        znet_release_resources (dev);

        return 0;
}

static void show_dma(struct net_device *dev)
{
        short ioaddr = dev->base_addr;
        unsigned char stat = inb (ioaddr);
        struct znet_private *znet = dev->priv;
        unsigned long flags;
        short dma_port = ((znet->tx_dma&3)<<2) + IO_DMA2_BASE;
        unsigned addr = inb(dma_port);
        short residue;

        addr |= inb(dma_port) << 8;
        residue = get_dma_residue(znet->tx_dma);

        if (znet_debug > 1) {
                flags=claim_dma_lock();
                printk(KERN_DEBUG "Stat:%02x Addr: %04x cnt:%3x\n",
                       stat, addr<<1, residue);
                release_dma_lock(flags);
        }
}

/* Initialize the hardware.  We have to do this when the board is open()ed
   or when we come out of suspend mode. */
static void hardware_init(struct net_device *dev)
{
        unsigned long flags;
        short ioaddr = dev->base_addr;
        struct znet_private *znet = dev->priv;

        znet->rx_cur = znet->rx_start;
        znet->tx_cur = znet->tx_start;

        /* Reset the chip, and start it up. */
        outb(OP0_RESET, ioaddr);

        flags=claim_dma_lock();
        disable_dma(znet->rx_dma);              /* reset by an interrupting task. */
        clear_dma_ff(znet->rx_dma);
        set_dma_mode(znet->rx_dma, DMA_RX_MODE);
        set_dma_addr(znet->rx_dma, (unsigned int) znet->rx_start);
        set_dma_count(znet->rx_dma, RX_BUF_SIZE);
        enable_dma(znet->rx_dma);
        /* Now set up the Tx channel. */
        disable_dma(znet->tx_dma);
        clear_dma_ff(znet->tx_dma);
        set_dma_mode(znet->tx_dma, DMA_TX_MODE);
        set_dma_addr(znet->tx_dma, (unsigned int) znet->tx_start);
        set_dma_count(znet->tx_dma, znet->tx_buf_len<<1);
        enable_dma(znet->tx_dma);
        release_dma_lock(flags);

        if (znet_debug > 1)
          printk(KERN_DEBUG "%s: Initializing the i82593, rx buf %p tx buf %p\n",
                         dev->name, znet->rx_start,znet->tx_start);
        /* Do an empty configure command, just like the Crynwr driver.  This
           resets to chip to its default values. */
        *znet->tx_cur++ = 0;
        *znet->tx_cur++ = 0;
        show_dma(dev);
        outb(OP0_CONFIGURE | CR0_CHNL, ioaddr);

        znet_set_multicast_list (dev);

        *znet->tx_cur++ = 6;
        memcpy(znet->tx_cur, dev->dev_addr, 6);
        znet->tx_cur += 3;
        show_dma(dev);
        outb(OP0_IA_SETUP | CR0_CHNL, ioaddr);
        show_dma(dev);

        update_stop_hit(ioaddr, 8192);
        if (znet_debug > 1)  printk(KERN_DEBUG "enabling Rx.\n");
        outb(OP0_RCV_ENABLE, ioaddr);
        netif_start_queue (dev);
}

static void update_stop_hit(short ioaddr, unsigned short rx_stop_offset)
{
        outb(OP0_SWIT_TO_PORT_1 | CR0_CHNL, ioaddr);
        if (znet_debug > 5)
          printk(KERN_DEBUG "Updating stop hit with value %02x.\n",
                         (rx_stop_offset >> 6) | CR1_STOP_REG_UPDATE);
        outb((rx_stop_offset >> 6) | CR1_STOP_REG_UPDATE, ioaddr);
        outb(OP1_SWIT_TO_PORT_0, ioaddr);
}

static __exit void znet_cleanup (void)
{
        if (znet_dev) {
                struct znet_private *znet = znet_dev->priv;

                unregister_netdev (znet_dev);
                kfree (znet->rx_start);
                kfree (znet->tx_start);
                free_netdev (znet_dev);
        }
}

module_init (znet_probe);
module_exit (znet_cleanup);