atari_scsi.c

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/*
 * atari_scsi.c -- Device dependent functions for the Atari generic SCSI port
 *
 * Copyright 1994 Roman Hodek <[email protected]>
 *
 *   Loosely based on the work of Robert De Vries' team and added:
 *    - working real DMA
 *    - Falcon support (untested yet!)   ++bjoern fixed and now it works
 *    - lots of extensions and bug fixes.
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file COPYING in the main directory of this archive
 * for more details.
 *
 */


/**************************************************************************/
/*                                                                        */
/* Notes for Falcon SCSI:                                                 */
/* ----------------------                                                 */
/*                                                                        */
/* Since the Falcon SCSI uses the ST-DMA chip, that is shared among       */
/* several device drivers, locking and unlocking the access to this       */
/* chip is required. But locking is not possible from an interrupt,       */
/* since it puts the process to sleep if the lock is not available.       */
/* This prevents "late" locking of the DMA chip, i.e. locking it just     */
/* before using it, since in case of disconnection-reconnection           */
/* commands, the DMA is started from the reselection interrupt.           */
/*                                                                        */
/* Two possible schemes for ST-DMA-locking would be:                      */
/*  1) The lock is taken for each command separately and disconnecting    */
/*     is forbidden (i.e. can_queue = 1).                                 */
/*  2) The DMA chip is locked when the first command comes in and         */
/*     released when the last command is finished and all queues are      */
/*     empty.                                                             */
/* The first alternative would result in bad performance, since the       */
/* interleaving of commands would not be used. The second is unfair to    */
/* other drivers using the ST-DMA, because the queues will seldom be      */
/* totally empty if there is a lot of disk traffic.                       */
/*                                                                        */
/* For this reasons I decided to employ a more elaborate scheme:          */
/*  - First, we give up the lock every time we can (for fairness), this    */
/*    means every time a command finishes and there are no other commands */
/*    on the disconnected queue.                                          */
/*  - If there are others waiting to lock the DMA chip, we stop           */
/*    issuing commands, i.e. moving them onto the issue queue.           */
/*    Because of that, the disconnected queue will run empty in a         */
/*    while. Instead we go to sleep on a 'fairness_queue'.                */
/*  - If the lock is released, all processes waiting on the fairness      */
/*    queue will be woken. The first of them tries to re-lock the DMA,     */
/*    the others wait for the first to finish this task. After that,      */
/*    they can all run on and do their commands...                        */
/* This sounds complicated (and it is it :-(), but it seems to be a       */
/* good compromise between fairness and performance: As long as no one     */
/* else wants to work with the ST-DMA chip, SCSI can go along as          */
/* usual. If now someone else comes, this behaviour is changed to a       */
/* "fairness mode": just already initiated commands are finished and      */
/* then the lock is released. The other one waiting will probably win     */
/* the race for locking the DMA, since it was waiting for longer. And     */
/* after it has finished, SCSI can go ahead again. Finally: I hope I      */
/* have not produced any deadlock possibilities!                          */
/*                                                                        */
/**************************************************************************/



#include <linux/module.h>

#define NDEBUG (0)

#define NDEBUG_ABORT        0x00100000
#define NDEBUG_TAGS     0x00200000
#define NDEBUG_MERGING      0x00400000

#define AUTOSENSE
/* For the Atari version, use only polled IO or REAL_DMA */
#define REAL_DMA
/* Support tagged queuing? (on devices that are able to... :-) */
#define SUPPORT_TAGS
#define MAX_TAGS 32

#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/ctype.h>
#include <linux/delay.h>
#include <linux/mm.h>
#include <linux/blkdev.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/nvram.h>
#include <linux/bitops.h>

#include <asm/setup.h>
#include <asm/atarihw.h>
#include <asm/atariints.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/irq.h>
#include <asm/traps.h>

#include "scsi.h"
#include <scsi/scsi_host.h>
#include "atari_scsi.h"
#include "NCR5380.h"
#include <asm/atari_stdma.h>
#include <asm/atari_stram.h>
#include <asm/io.h>

#include <linux/stat.h>

#define IS_A_TT()   ATARIHW_PRESENT(TT_SCSI)

#define SCSI_DMA_WRITE_P(elt,val)               \
    do {                            \
        unsigned long v = val;              \
        tt_scsi_dma.elt##_lo = v & 0xff;        \
        v >>= 8;                    \
        tt_scsi_dma.elt##_lmd = v & 0xff;       \
        v >>= 8;                    \
        tt_scsi_dma.elt##_hmd = v & 0xff;       \
        v >>= 8;                    \
        tt_scsi_dma.elt##_hi = v & 0xff;        \
    } while(0)

#define SCSI_DMA_READ_P(elt)                    \
    (((((((unsigned long)tt_scsi_dma.elt##_hi << 8) |   \
         (unsigned long)tt_scsi_dma.elt##_hmd) << 8) |  \
       (unsigned long)tt_scsi_dma.elt##_lmd) << 8) |    \
     (unsigned long)tt_scsi_dma.elt##_lo)


static inline void SCSI_DMA_SETADR(unsigned long adr)
{
    st_dma.dma_lo = (unsigned char)adr;
    MFPDELAY();
    adr >>= 8;
    st_dma.dma_md = (unsigned char)adr;
    MFPDELAY();
    adr >>= 8;
    st_dma.dma_hi = (unsigned char)adr;
    MFPDELAY();
}

static inline unsigned long SCSI_DMA_GETADR(void)
{
    unsigned long adr;
    adr = st_dma.dma_lo;
    MFPDELAY();
    adr |= (st_dma.dma_md & 0xff) << 8;
    MFPDELAY();
    adr |= (st_dma.dma_hi & 0xff) << 16;
    MFPDELAY();
    return adr;
}

static inline void ENABLE_IRQ(void)
{
    if (IS_A_TT())
        atari_enable_irq(IRQ_TT_MFP_SCSI);
    else
        atari_enable_irq(IRQ_MFP_FSCSI);
}

static inline void DISABLE_IRQ(void)
{
    if (IS_A_TT())
        atari_disable_irq(IRQ_TT_MFP_SCSI);
    else
        atari_disable_irq(IRQ_MFP_FSCSI);
}


#define HOSTDATA_DMALEN     (((struct NCR5380_hostdata *) \
                (atari_scsi_host->hostdata))->dma_len)

/* Time (in jiffies) to wait after a reset; the SCSI standard calls for 250ms,
 * we usually do 0.5s to be on the safe side. But Toshiba CD-ROMs once more
 * need ten times the standard value... */
#ifndef CONFIG_ATARI_SCSI_TOSHIBA_DELAY
#define AFTER_RESET_DELAY   (HZ/2)
#else
#define AFTER_RESET_DELAY   (5*HZ/2)
#endif

/***************************** Prototypes *****************************/

#ifdef REAL_DMA
static int scsi_dma_is_ignored_buserr(unsigned char dma_stat);
static void atari_scsi_fetch_restbytes(void);
static long atari_scsi_dma_residual(struct Scsi_Host *instance);
static int falcon_classify_cmd(Scsi_Cmnd *cmd);
static unsigned long atari_dma_xfer_len(unsigned long wanted_len,
                    Scsi_Cmnd *cmd, int write_flag);
#endif
static irqreturn_t scsi_tt_intr(int irq, void *dummy);
static irqreturn_t scsi_falcon_intr(int irq, void *dummy);
static void falcon_release_lock_if_possible(struct NCR5380_hostdata *hostdata);
static void falcon_get_lock(void);
#ifdef CONFIG_ATARI_SCSI_RESET_BOOT
static void atari_scsi_reset_boot(void);
#endif
static unsigned char atari_scsi_tt_reg_read(unsigned char reg);
static void atari_scsi_tt_reg_write(unsigned char reg, unsigned char value);
static unsigned char atari_scsi_falcon_reg_read(unsigned char reg);
static void atari_scsi_falcon_reg_write(unsigned char reg, unsigned char value);

/************************* End of Prototypes **************************/


static struct Scsi_Host *atari_scsi_host;
static unsigned char (*atari_scsi_reg_read)(unsigned char reg);
static void (*atari_scsi_reg_write)(unsigned char reg, unsigned char value);

#ifdef REAL_DMA
static unsigned long    atari_dma_residual, atari_dma_startaddr;
static short        atari_dma_active;
/* pointer to the dribble buffer */
static char     *atari_dma_buffer;
/* precalculated physical address of the dribble buffer */
static unsigned long    atari_dma_phys_buffer;
/* != 0 tells the Falcon int handler to copy data from the dribble buffer */
static char     *atari_dma_orig_addr;
/* size of the dribble buffer; 4k seems enough, since the Falcon cannot use
 * scatter-gather anyway, so most transfers are 1024 byte only. In the rare
 * cases where requests to physical contiguous buffers have been merged, this
 * request is <= 4k (one page). So I don't think we have to split transfers
 * just due to this buffer size...
 */
#define STRAM_BUFFER_SIZE   (4096)
/* mask for address bits that can't be used with the ST-DMA */
static unsigned long    atari_dma_stram_mask;
#define STRAM_ADDR(a)   (((a) & atari_dma_stram_mask) == 0)
/* number of bytes to cut from a transfer to handle NCR overruns */
static int atari_read_overruns;
#endif

static int setup_can_queue = -1;
module_param(setup_can_queue, int, 0);
static int setup_cmd_per_lun = -1;
module_param(setup_cmd_per_lun, int, 0);
static int setup_sg_tablesize = -1;
module_param(setup_sg_tablesize, int, 0);
#ifdef SUPPORT_TAGS
static int setup_use_tagged_queuing = -1;
module_param(setup_use_tagged_queuing, int, 0);
#endif
static int setup_hostid = -1;
module_param(setup_hostid, int, 0);


#if defined(REAL_DMA)

static int scsi_dma_is_ignored_buserr(unsigned char dma_stat)
{
    int i;
    unsigned long addr = SCSI_DMA_READ_P(dma_addr), end_addr;

    if (dma_stat & 0x01) {

        /* A bus error happens when DMA-ing from the last page of a
         * physical memory chunk (DMA prefetch!), but that doesn't hurt.
         * Check for this case:
         */

        for (i = 0; i < m68k_num_memory; ++i) {
            end_addr = m68k_memory[i].addr + m68k_memory[i].size;
            if (end_addr <= addr && addr <= end_addr + 4)
                return 1;
        }
    }
    return 0;
}


#if 0
/* Dead code... wasn't called anyway :-) and causes some trouble, because at
 * end-of-DMA, both SCSI ints are triggered simultaneously, so the NCR int has
 * to clear the DMA int pending bit before it allows other level 6 interrupts.
 */
static void scsi_dma_buserr(int irq, void *dummy)
{
    unsigned char dma_stat = tt_scsi_dma.dma_ctrl;

    /* Don't do anything if a NCR interrupt is pending. Probably it's just
     * masked... */
    if (atari_irq_pending(IRQ_TT_MFP_SCSI))
        return;

    printk("Bad SCSI DMA interrupt! dma_addr=0x%08lx dma_stat=%02x dma_cnt=%08lx\n",
           SCSI_DMA_READ_P(dma_addr), dma_stat, SCSI_DMA_READ_P(dma_cnt));
    if (dma_stat & 0x80) {
        if (!scsi_dma_is_ignored_buserr(dma_stat))
            printk("SCSI DMA bus error -- bad DMA programming!\n");
    } else {
        /* Under normal circumstances we never should get to this point,
         * since both interrupts are triggered simultaneously and the 5380
         * int has higher priority. When this irq is handled, that DMA
         * interrupt is cleared. So a warning message is printed here.
         */
        printk("SCSI DMA intr ?? -- this shouldn't happen!\n");
    }
}
#endif

#endif


static irqreturn_t scsi_tt_intr(int irq, void *dummy)
{
#ifdef REAL_DMA
    int dma_stat;

    dma_stat = tt_scsi_dma.dma_ctrl;

    INT_PRINTK("scsi%d: NCR5380 interrupt, DMA status = %02x\n",
           atari_scsi_host->host_no, dma_stat & 0xff);

    /* Look if it was the DMA that has interrupted: First possibility
     * is that a bus error occurred...
     */
    if (dma_stat & 0x80) {
        if (!scsi_dma_is_ignored_buserr(dma_stat)) {
            printk(KERN_ERR "SCSI DMA caused bus error near 0x%08lx\n",
                   SCSI_DMA_READ_P(dma_addr));
            printk(KERN_CRIT "SCSI DMA bus error -- bad DMA programming!");
        }
    }

    /* If the DMA is active but not finished, we have the case
     * that some other 5380 interrupt occurred within the DMA transfer.
     * This means we have residual bytes, if the desired end address
     * is not yet reached. Maybe we have to fetch some bytes from the
     * rest data register, too. The residual must be calculated from
     * the address pointer, not the counter register, because only the
     * addr reg counts bytes not yet written and pending in the rest
     * data reg!
     */
    if ((dma_stat & 0x02) && !(dma_stat & 0x40)) {
        atari_dma_residual = HOSTDATA_DMALEN - (SCSI_DMA_READ_P(dma_addr) - atari_dma_startaddr);

        DMA_PRINTK("SCSI DMA: There are %ld residual bytes.\n",
               atari_dma_residual);

        if ((signed int)atari_dma_residual < 0)
            atari_dma_residual = 0;
        if ((dma_stat & 1) == 0) {
            /*
             * After read operations, we maybe have to
             * transport some rest bytes
             */
            atari_scsi_fetch_restbytes();
        } else {
            /*
             * There seems to be a nasty bug in some SCSI-DMA/NCR
             * combinations: If a target disconnects while a write
             * operation is going on, the address register of the
             * DMA may be a few bytes farer than it actually read.
             * This is probably due to DMA prefetching and a delay
             * between DMA and NCR.  Experiments showed that the
             * dma_addr is 9 bytes to high, but this could vary.
             * The problem is, that the residual is thus calculated
             * wrong and the next transfer will start behind where
             * it should.  So we round up the residual to the next
             * multiple of a sector size, if it isn't already a
             * multiple and the originally expected transfer size
             * was.  The latter condition is there to ensure that
             * the correction is taken only for "real" data
             * transfers and not for, e.g., the parameters of some
             * other command.  These shouldn't disconnect anyway.
             */
            if (atari_dma_residual & 0x1ff) {
                DMA_PRINTK("SCSI DMA: DMA bug corrected, "
                       "difference %ld bytes\n",
                       512 - (atari_dma_residual & 0x1ff));
                atari_dma_residual = (atari_dma_residual + 511) & ~0x1ff;
            }
        }
        tt_scsi_dma.dma_ctrl = 0;
    }

    /* If the DMA is finished, fetch the rest bytes and turn it off */
    if (dma_stat & 0x40) {
        atari_dma_residual = 0;
        if ((dma_stat & 1) == 0)
            atari_scsi_fetch_restbytes();
        tt_scsi_dma.dma_ctrl = 0;
    }

#endif /* REAL_DMA */

    NCR5380_intr(irq, dummy);

#if 0
    /* To be sure the int is not masked */
    atari_enable_irq(IRQ_TT_MFP_SCSI);
#endif
    return IRQ_HANDLED;
}


static irqreturn_t scsi_falcon_intr(int irq, void *dummy)
{
#ifdef REAL_DMA
    int dma_stat;

    /* Turn off DMA and select sector counter register before
     * accessing the status register (Atari recommendation!)
     */
    st_dma.dma_mode_status = 0x90;
    dma_stat = st_dma.dma_mode_status;

    /* Bit 0 indicates some error in the DMA process... don't know
     * what happened exactly (no further docu).
     */
    if (!(dma_stat & 0x01)) {
        /* DMA error */
        printk(KERN_CRIT "SCSI DMA error near 0x%08lx!\n", SCSI_DMA_GETADR());
    }

    /* If the DMA was active, but now bit 1 is not clear, it is some
     * other 5380 interrupt that finishes the DMA transfer. We have to
     * calculate the number of residual bytes and give a warning if
     * bytes are stuck in the ST-DMA fifo (there's no way to reach them!)
     */
    if (atari_dma_active && (dma_stat & 0x02)) {
        unsigned long transferred;

        transferred = SCSI_DMA_GETADR() - atari_dma_startaddr;
        /* The ST-DMA address is incremented in 2-byte steps, but the
         * data are written only in 16-byte chunks. If the number of
         * transferred bytes is not divisible by 16, the remainder is
         * lost somewhere in outer space.
         */
        if (transferred & 15)
            printk(KERN_ERR "SCSI DMA error: %ld bytes lost in "
                   "ST-DMA fifo\n", transferred & 15);

        atari_dma_residual = HOSTDATA_DMALEN - transferred;
        DMA_PRINTK("SCSI DMA: There are %ld residual bytes.\n",
               atari_dma_residual);
    } else
        atari_dma_residual = 0;
    atari_dma_active = 0;

    if (atari_dma_orig_addr) {
        /* If the dribble buffer was used on a read operation, copy the DMA-ed
         * data to the original destination address.
         */
        memcpy(atari_dma_orig_addr, phys_to_virt(atari_dma_startaddr),
               HOSTDATA_DMALEN - atari_dma_residual);
        atari_dma_orig_addr = NULL;
    }

#endif /* REAL_DMA */

    NCR5380_intr(irq, dummy);
    return IRQ_HANDLED;
}


#ifdef REAL_DMA
static void atari_scsi_fetch_restbytes(void)
{
    int nr;
    char *src, *dst;
    unsigned long phys_dst;

    /* fetch rest bytes in the DMA register */
    phys_dst = SCSI_DMA_READ_P(dma_addr);
    nr = phys_dst & 3;
    if (nr) {
        /* there are 'nr' bytes left for the last long address
           before the DMA pointer */
        phys_dst ^= nr;
        DMA_PRINTK("SCSI DMA: there are %d rest bytes for phys addr 0x%08lx",
               nr, phys_dst);
        /* The content of the DMA pointer is a physical address!  */
        dst = phys_to_virt(phys_dst);
        DMA_PRINTK(" = virt addr %p\n", dst);
        for (src = (char *)&tt_scsi_dma.dma_restdata; nr != 0; --nr)
            *dst++ = *src++;
    }
}
#endif /* REAL_DMA */


static int falcon_got_lock = 0;
static DECLARE_WAIT_QUEUE_HEAD(falcon_fairness_wait);
static int falcon_trying_lock = 0;
static DECLARE_WAIT_QUEUE_HEAD(falcon_try_wait);
static int falcon_dont_release = 0;

/* This function releases the lock on the DMA chip if there is no
 * connected command and the disconnected queue is empty. On
 * releasing, instances of falcon_get_lock are awoken, that put
 * themselves to sleep for fairness. They can now try to get the lock
 * again (but others waiting longer more probably will win).
 */

static void falcon_release_lock_if_possible(struct NCR5380_hostdata *hostdata)
{
    unsigned long flags;

    if (IS_A_TT())
        return;

    local_irq_save(flags);

    if (falcon_got_lock && !hostdata->disconnected_queue &&
        !hostdata->issue_queue && !hostdata->connected) {

        if (falcon_dont_release) {
#if 0
            printk("WARNING: Lock release not allowed. Ignored\n");
#endif
            local_irq_restore(flags);
            return;
        }
        falcon_got_lock = 0;
        stdma_release();
        wake_up(&falcon_fairness_wait);
    }

    local_irq_restore(flags);
}

/* This function manages the locking of the ST-DMA.
 * If the DMA isn't locked already for SCSI, it tries to lock it by
 * calling stdma_lock(). But if the DMA is locked by the SCSI code and
 * there are other drivers waiting for the chip, we do not issue the
 * command immediately but wait on 'falcon_fairness_queue'. We will be
 * waked up when the DMA is unlocked by some SCSI interrupt. After that
 * we try to get the lock again.
 * But we must be prepared that more than one instance of
 * falcon_get_lock() is waiting on the fairness queue. They should not
 * try all at once to call stdma_lock(), one is enough! For that, the
 * first one sets 'falcon_trying_lock', others that see that variable
 * set wait on the queue 'falcon_try_wait'.
 * Complicated, complicated.... Sigh...
 */

static void falcon_get_lock(void)
{
    unsigned long flags;

    if (IS_A_TT())
        return;

    local_irq_save(flags);

    while (!in_irq() && falcon_got_lock && stdma_others_waiting())
        sleep_on(&falcon_fairness_wait);

    while (!falcon_got_lock) {
        if (in_irq())
            panic("Falcon SCSI hasn't ST-DMA lock in interrupt");
        if (!falcon_trying_lock) {
            falcon_trying_lock = 1;
            stdma_lock(scsi_falcon_intr, NULL);
            falcon_got_lock = 1;
            falcon_trying_lock = 0;
            wake_up(&falcon_try_wait);
        } else {
            sleep_on(&falcon_try_wait);
        }
    }

    local_irq_restore(flags);
    if (!falcon_got_lock)
        panic("Falcon SCSI: someone stole the lock :-(\n");
}


static int __init atari_scsi_detect(struct scsi_host_template *host)
{
    static int called = 0;
    struct Scsi_Host *instance;

    if (!MACH_IS_ATARI ||
        (!ATARIHW_PRESENT(ST_SCSI) && !ATARIHW_PRESENT(TT_SCSI)) ||
        called)
        return 0;

    host->proc_name = "Atari";

    atari_scsi_reg_read  = IS_A_TT() ? atari_scsi_tt_reg_read :
                       atari_scsi_falcon_reg_read;
    atari_scsi_reg_write = IS_A_TT() ? atari_scsi_tt_reg_write :
                       atari_scsi_falcon_reg_write;

    /* setup variables */
    host->can_queue =
        (setup_can_queue > 0) ? setup_can_queue :
        IS_A_TT() ? ATARI_TT_CAN_QUEUE : ATARI_FALCON_CAN_QUEUE;
    host->cmd_per_lun =
        (setup_cmd_per_lun > 0) ? setup_cmd_per_lun :
        IS_A_TT() ? ATARI_TT_CMD_PER_LUN : ATARI_FALCON_CMD_PER_LUN;
    /* Force sg_tablesize to 0 on a Falcon! */
    host->sg_tablesize =
        !IS_A_TT() ? ATARI_FALCON_SG_TABLESIZE :
        (setup_sg_tablesize >= 0) ? setup_sg_tablesize : ATARI_TT_SG_TABLESIZE;

    if (setup_hostid >= 0)
        host->this_id = setup_hostid;
    else {
        /* use 7 as default */
        host->this_id = 7;
        /* Test if a host id is set in the NVRam */
        if (ATARIHW_PRESENT(TT_CLK) && nvram_check_checksum()) {
            unsigned char b = nvram_read_byte( 14 );
            /* Arbitration enabled? (for TOS) If yes, use configured host ID */
            if (b & 0x80)
                host->this_id = b & 7;
        }
    }

#ifdef SUPPORT_TAGS
    if (setup_use_tagged_queuing < 0)
        setup_use_tagged_queuing = DEFAULT_USE_TAGGED_QUEUING;
#endif
#ifdef REAL_DMA
    /* If running on a Falcon and if there's TT-Ram (i.e., more than one
     * memory block, since there's always ST-Ram in a Falcon), then allocate a
     * STRAM_BUFFER_SIZE byte dribble buffer for transfers from/to alternative
     * Ram.
     */
    if (MACH_IS_ATARI && ATARIHW_PRESENT(ST_SCSI) &&
        !ATARIHW_PRESENT(EXTD_DMA) && m68k_num_memory > 1) {
        atari_dma_buffer = atari_stram_alloc(STRAM_BUFFER_SIZE, "SCSI");
        if (!atari_dma_buffer) {
            printk(KERN_ERR "atari_scsi_detect: can't allocate ST-RAM "
                    "double buffer\n");
            return 0;
        }
        atari_dma_phys_buffer = virt_to_phys(atari_dma_buffer);
        atari_dma_orig_addr = 0;
    }
#endif
    instance = scsi_register(host, sizeof(struct NCR5380_hostdata));
    if (instance == NULL) {
        atari_stram_free(atari_dma_buffer);
        atari_dma_buffer = 0;
        return 0;
    }
    atari_scsi_host = instance;
    /*
     * Set irq to 0, to avoid that the mid-level code disables our interrupt
     * during queue_command calls. This is completely unnecessary, and even
     * worse causes bad problems on the Falcon, where the int is shared with
     * IDE and floppy!
     */
       instance->irq = 0;

#ifdef CONFIG_ATARI_SCSI_RESET_BOOT
    atari_scsi_reset_boot();
#endif
    NCR5380_init(instance, 0);

    if (IS_A_TT()) {

        /* This int is actually "pseudo-slow", i.e. it acts like a slow
         * interrupt after having cleared the pending flag for the DMA
         * interrupt. */
        if (request_irq(IRQ_TT_MFP_SCSI, scsi_tt_intr, IRQ_TYPE_SLOW,
                 "SCSI NCR5380", instance)) {
            printk(KERN_ERR "atari_scsi_detect: cannot allocate irq %d, aborting",IRQ_TT_MFP_SCSI);
            scsi_unregister(atari_scsi_host);
            atari_stram_free(atari_dma_buffer);
            atari_dma_buffer = 0;
            return 0;
        }
        tt_mfp.active_edge |= 0x80;     /* SCSI int on L->H */
#ifdef REAL_DMA
        tt_scsi_dma.dma_ctrl = 0;
        atari_dma_residual = 0;

        if (MACH_IS_MEDUSA) {
            /* While the read overruns (described by Drew Eckhardt in
             * NCR5380.c) never happened on TTs, they do in fact on the Medusa
             * (This was the cause why SCSI didn't work right for so long
             * there.) Since handling the overruns slows down a bit, I turned
             * the #ifdef's into a runtime condition.
             *
             * In principle it should be sufficient to do max. 1 byte with
             * PIO, but there is another problem on the Medusa with the DMA
             * rest data register. So 'atari_read_overruns' is currently set
             * to 4 to avoid having transfers that aren't a multiple of 4. If
             * the rest data bug is fixed, this can be lowered to 1.
             */
            atari_read_overruns = 4;
        }
#endif /*REAL_DMA*/
    } else { /* ! IS_A_TT */

        /* Nothing to do for the interrupt: the ST-DMA is initialized
         * already by atari_init_INTS()
         */

#ifdef REAL_DMA
        atari_dma_residual = 0;
        atari_dma_active = 0;
        atari_dma_stram_mask = (ATARIHW_PRESENT(EXTD_DMA) ? 0x00000000
                    : 0xff000000);
#endif
    }

    printk(KERN_INFO "scsi%d: options CAN_QUEUE=%d CMD_PER_LUN=%d SCAT-GAT=%d "
#ifdef SUPPORT_TAGS
            "TAGGED-QUEUING=%s "
#endif
            "HOSTID=%d",
            instance->host_no, instance->hostt->can_queue,
            instance->hostt->cmd_per_lun,
            instance->hostt->sg_tablesize,
#ifdef SUPPORT_TAGS
            setup_use_tagged_queuing ? "yes" : "no",
#endif
            instance->hostt->this_id );
    NCR5380_print_options(instance);
    printk("\n");

    called = 1;
    return 1;
}

static int atari_scsi_release(struct Scsi_Host *sh)
{
    if (IS_A_TT())
        free_irq(IRQ_TT_MFP_SCSI, sh);
    if (atari_dma_buffer)
        atari_stram_free(atari_dma_buffer);
    NCR5380_exit(sh);
    return 1;
}

#ifndef MODULE
static int __init atari_scsi_setup(char *str)
{
    /* Format of atascsi parameter is:
     *   atascsi=<can_queue>,<cmd_per_lun>,<sg_tablesize>,<hostid>,<use_tags>
     * Defaults depend on TT or Falcon, hostid determined at run time.
     * Negative values mean don't change.
     */
    int ints[6];

    get_options(str, ARRAY_SIZE(ints), ints);

    if (ints[0] < 1) {
        printk("atari_scsi_setup: no arguments!\n");
        return 0;
    }

    if (ints[0] >= 1) {
        if (ints[1] > 0)
            /* no limits on this, just > 0 */
            setup_can_queue = ints[1];
    }
    if (ints[0] >= 2) {
        if (ints[2] > 0)
            setup_cmd_per_lun = ints[2];
    }
    if (ints[0] >= 3) {
        if (ints[3] >= 0) {
            setup_sg_tablesize = ints[3];
            /* Must be <= SG_ALL (255) */
            if (setup_sg_tablesize > SG_ALL)
                setup_sg_tablesize = SG_ALL;
        }
    }
    if (ints[0] >= 4) {
        /* Must be between 0 and 7 */
        if (ints[4] >= 0 && ints[4] <= 7)
            setup_hostid = ints[4];
        else if (ints[4] > 7)
            printk("atari_scsi_setup: invalid host ID %d !\n", ints[4]);
    }
#ifdef SUPPORT_TAGS
    if (ints[0] >= 5) {
        if (ints[5] >= 0)
            setup_use_tagged_queuing = !!ints[5];
    }
#endif

    return 1;
}

__setup("atascsi=", atari_scsi_setup);
#endif /* !MODULE */

static int atari_scsi_bus_reset(Scsi_Cmnd *cmd)
{
    int rv;
    struct NCR5380_hostdata *hostdata =
        (struct NCR5380_hostdata *)cmd->device->host->hostdata;

    /* For doing the reset, SCSI interrupts must be disabled first,
     * since the 5380 raises its IRQ line while _RST is active and we
     * can't disable interrupts completely, since we need the timer.
     */
    /* And abort a maybe active DMA transfer */
    if (IS_A_TT()) {
        atari_turnoff_irq(IRQ_TT_MFP_SCSI);
#ifdef REAL_DMA
        tt_scsi_dma.dma_ctrl = 0;
#endif /* REAL_DMA */
    } else {
        atari_turnoff_irq(IRQ_MFP_FSCSI);
#ifdef REAL_DMA
        st_dma.dma_mode_status = 0x90;
        atari_dma_active = 0;
        atari_dma_orig_addr = NULL;
#endif /* REAL_DMA */
    }

    rv = NCR5380_bus_reset(cmd);

    /* Re-enable ints */
    if (IS_A_TT()) {
        atari_turnon_irq(IRQ_TT_MFP_SCSI);
    } else {
        atari_turnon_irq(IRQ_MFP_FSCSI);
    }
    if ((rv & SCSI_RESET_ACTION) == SCSI_RESET_SUCCESS)
        falcon_release_lock_if_possible(hostdata);

    return rv;
}


#ifdef CONFIG_ATARI_SCSI_RESET_BOOT
static void __init atari_scsi_reset_boot(void)
{
    unsigned long end;

    /*
     * Do a SCSI reset to clean up the bus during initialization. No messing
     * with the queues, interrupts, or locks necessary here.
     */

    printk("Atari SCSI: resetting the SCSI bus...");

    /* get in phase */
    NCR5380_write(TARGET_COMMAND_REG,
              PHASE_SR_TO_TCR(NCR5380_read(STATUS_REG)));

    /* assert RST */
    NCR5380_write(INITIATOR_COMMAND_REG, ICR_BASE | ICR_ASSERT_RST);
    /* The min. reset hold time is 25us, so 40us should be enough */
    udelay(50);
    /* reset RST and interrupt */
    NCR5380_write(INITIATOR_COMMAND_REG, ICR_BASE);
    NCR5380_read(RESET_PARITY_INTERRUPT_REG);

    end = jiffies + AFTER_RESET_DELAY;
    while (time_before(jiffies, end))
        barrier();

    printk(" done\n");
}
#endif


static const char *atari_scsi_info(struct Scsi_Host *host)
{
    /* atari_scsi_detect() is verbose enough... */
    static const char string[] = "Atari native SCSI";
    return string;
}


#if defined(REAL_DMA)

static unsigned long atari_scsi_dma_setup(struct Scsi_Host *instance,
                      void *data, unsigned long count,
                      int dir)
{
    unsigned long addr = virt_to_phys(data);

    DMA_PRINTK("scsi%d: setting up dma, data = %p, phys = %lx, count = %ld, "
           "dir = %d\n", instance->host_no, data, addr, count, dir);

    if (!IS_A_TT() && !STRAM_ADDR(addr)) {
        /* If we have a non-DMAable address on a Falcon, use the dribble
         * buffer; 'orig_addr' != 0 in the read case tells the interrupt
         * handler to copy data from the dribble buffer to the originally
         * wanted address.
         */
        if (dir)
            memcpy(atari_dma_buffer, data, count);
        else
            atari_dma_orig_addr = data;
        addr = atari_dma_phys_buffer;
    }

    atari_dma_startaddr = addr; /* Needed for calculating residual later. */

    /* Cache cleanup stuff: On writes, push any dirty cache out before sending
     * it to the peripheral. (Must be done before DMA setup, since at least
     * the ST-DMA begins to fill internal buffers right after setup. For
     * reads, invalidate any cache, may be altered after DMA without CPU
     * knowledge.
     *
     * ++roman: For the Medusa, there's no need at all for that cache stuff,
     * because the hardware does bus snooping (fine!).
     */
    dma_cache_maintenance(addr, count, dir);

    if (count == 0)
        printk(KERN_NOTICE "SCSI warning: DMA programmed for 0 bytes !\n");

    if (IS_A_TT()) {
        tt_scsi_dma.dma_ctrl = dir;
        SCSI_DMA_WRITE_P(dma_addr, addr);
        SCSI_DMA_WRITE_P(dma_cnt, count);
        tt_scsi_dma.dma_ctrl = dir | 2;
    } else { /* ! IS_A_TT */

        /* set address */
        SCSI_DMA_SETADR(addr);

        /* toggle direction bit to clear FIFO and set DMA direction */
        dir <<= 8;
        st_dma.dma_mode_status = 0x90 | dir;
        st_dma.dma_mode_status = 0x90 | (dir ^ 0x100);
        st_dma.dma_mode_status = 0x90 | dir;
        udelay(40);
        /* On writes, round up the transfer length to the next multiple of 512
         * (see also comment at atari_dma_xfer_len()). */
        st_dma.fdc_acces_seccount = (count + (dir ? 511 : 0)) >> 9;
        udelay(40);
        st_dma.dma_mode_status = 0x10 | dir;
        udelay(40);
        /* need not restore value of dir, only boolean value is tested */
        atari_dma_active = 1;
    }

    return count;
}


static long atari_scsi_dma_residual(struct Scsi_Host *instance)
{
    return atari_dma_residual;
}


#define CMD_SURELY_BLOCK_MODE   0
#define CMD_SURELY_BYTE_MODE    1
#define CMD_MODE_UNKNOWN        2

static int falcon_classify_cmd(Scsi_Cmnd *cmd)
{
    unsigned char opcode = cmd->cmnd[0];

    if (opcode == READ_DEFECT_DATA || opcode == READ_LONG ||
        opcode == READ_BUFFER)
        return CMD_SURELY_BYTE_MODE;
    else if (opcode == READ_6 || opcode == READ_10 ||
         opcode == 0xa8 /* READ_12 */ || opcode == READ_REVERSE ||
         opcode == RECOVER_BUFFERED_DATA) {
        /* In case of a sequential-access target (tape), special care is
         * needed here: The transfer is block-mode only if the 'fixed' bit is
         * set! */
        if (cmd->device->type == TYPE_TAPE && !(cmd->cmnd[1] & 1))
            return CMD_SURELY_BYTE_MODE;
        else
            return CMD_SURELY_BLOCK_MODE;
    } else
        return CMD_MODE_UNKNOWN;
}


/* This function calculates the number of bytes that can be transferred via
 * DMA. On the TT, this is arbitrary, but on the Falcon we have to use the
 * ST-DMA chip. There are only multiples of 512 bytes possible and max.
 * 255*512 bytes :-( This means also, that defining READ_OVERRUNS is not
 * possible on the Falcon, since that would require to program the DMA for
 * n*512 - atari_read_overrun bytes. But it seems that the Falcon doesn't have
 * the overrun problem, so this question is academic :-)
 */

static unsigned long atari_dma_xfer_len(unsigned long wanted_len,
                    Scsi_Cmnd *cmd, int write_flag)
{
    unsigned long   possible_len, limit;

    if (IS_A_TT())
        /* TT SCSI DMA can transfer arbitrary #bytes */
        return wanted_len;

    /* ST DMA chip is stupid -- only multiples of 512 bytes! (and max.
     * 255*512 bytes, but this should be enough)
     *
     * ++roman: Aaargl! Another Falcon-SCSI problem... There are some commands
     * that return a number of bytes which cannot be known beforehand. In this
     * case, the given transfer length is an "allocation length". Now it
     * can happen that this allocation length is a multiple of 512 bytes and
     * the DMA is used. But if not n*512 bytes really arrive, some input data
     * will be lost in the ST-DMA's FIFO :-( Thus, we have to distinguish
     * between commands that do block transfers and those that do byte
     * transfers. But this isn't easy... there are lots of vendor specific
     * commands, and the user can issue any command via the
     * SCSI_IOCTL_SEND_COMMAND.
     *
     * The solution: We classify SCSI commands in 1) surely block-mode cmd.s,
     * 2) surely byte-mode cmd.s and 3) cmd.s with unknown mode. In case 1)
     * and 3), the thing to do is obvious: allow any number of blocks via DMA
     * or none. In case 2), we apply some heuristic: Byte mode is assumed if
     * the transfer (allocation) length is < 1024, hoping that no cmd. not
     * explicitly known as byte mode have such big allocation lengths...
     * BTW, all the discussion above applies only to reads. DMA writes are
     * unproblematic anyways, since the targets aborts the transfer after
     * receiving a sufficient number of bytes.
     *
     * Another point: If the transfer is from/to an non-ST-RAM address, we
     * use the dribble buffer and thus can do only STRAM_BUFFER_SIZE bytes.
     */

    if (write_flag) {
        /* Write operation can always use the DMA, but the transfer size must
         * be rounded up to the next multiple of 512 (atari_dma_setup() does
         * this).
         */
        possible_len = wanted_len;
    } else {
        /* Read operations: if the wanted transfer length is not a multiple of
         * 512, we cannot use DMA, since the ST-DMA cannot split transfers
         * (no interrupt on DMA finished!)
         */
        if (wanted_len & 0x1ff)
            possible_len = 0;
        else {
            /* Now classify the command (see above) and decide whether it is
             * allowed to do DMA at all */
            switch (falcon_classify_cmd(cmd)) {
            case CMD_SURELY_BLOCK_MODE:
                possible_len = wanted_len;
                break;
            case CMD_SURELY_BYTE_MODE:
                possible_len = 0; /* DMA prohibited */
                break;
            case CMD_MODE_UNKNOWN:
            default:
                /* For unknown commands assume block transfers if the transfer
                 * size/allocation length is >= 1024 */
                possible_len = (wanted_len < 1024) ? 0 : wanted_len;
                break;
            }
        }
    }

    /* Last step: apply the hard limit on DMA transfers */
    limit = (atari_dma_buffer && !STRAM_ADDR(virt_to_phys(cmd->SCp.ptr))) ?
            STRAM_BUFFER_SIZE : 255*512;
    if (possible_len > limit)
        possible_len = limit;

    if (possible_len != wanted_len)
        DMA_PRINTK("Sorry, must cut DMA transfer size to %ld bytes "
               "instead of %ld\n", possible_len, wanted_len);

    return possible_len;
}


#endif  /* REAL_DMA */


/* NCR5380 register access functions
 *
 * There are separate functions for TT and Falcon, because the access
 * methods are quite different. The calling macros NCR5380_read and
 * NCR5380_write call these functions via function pointers.
 */

static unsigned char atari_scsi_tt_reg_read(unsigned char reg)
{
    return tt_scsi_regp[reg * 2];
}

static void atari_scsi_tt_reg_write(unsigned char reg, unsigned char value)
{
    tt_scsi_regp[reg * 2] = value;
}

static unsigned char atari_scsi_falcon_reg_read(unsigned char reg)
{
    dma_wd.dma_mode_status= (u_short)(0x88 + reg);
    return (u_char)dma_wd.fdc_acces_seccount;
}

static void atari_scsi_falcon_reg_write(unsigned char reg, unsigned char value)
{
    dma_wd.dma_mode_status = (u_short)(0x88 + reg);
    dma_wd.fdc_acces_seccount = (u_short)value;
}


#include "atari_NCR5380.c"

static struct scsi_host_template driver_template = {
    .proc_info      = atari_scsi_proc_info,
    .name           = "Atari native SCSI",
    .detect         = atari_scsi_detect,
    .release        = atari_scsi_release,
    .info           = atari_scsi_info,
    .queuecommand       = atari_scsi_queue_command,
    .eh_abort_handler   = atari_scsi_abort,
    .eh_bus_reset_handler   = atari_scsi_bus_reset,
    .can_queue      = 0, /* initialized at run-time */
    .this_id        = 0, /* initialized at run-time */
    .sg_tablesize       = 0, /* initialized at run-time */
    .cmd_per_lun        = 0, /* initialized at run-time */
    .use_clustering     = DISABLE_CLUSTERING
};


#include "scsi_module.c"

MODULE_LICENSE("GPL");