[firefly-linux-kernel-4.4.55.git] / drivers / scsi / atari_scsi.c

/*
 * atari_scsi.c -- Device dependent functions for the Atari generic SCSI port
 *
 * Copyright 1994 Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>
 *
 *   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>
#include <linux/types.h>
#include <linux/delay.h>
#include <linux/blkdev.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/nvram.h>
#include <linux/bitops.h>
#include <linux/wait.h>
#include <linux/platform_device.h>

#include <asm/setup.h>
#include <asm/atarihw.h>
#include <asm/atariints.h>
#include <asm/atari_stdma.h>
#include <asm/atari_stram.h>
#include <asm/io.h>

#include <scsi/scsi_host.h>

/* Definitions for the core NCR5380 driver. */

#define REAL_DMA
#define SUPPORT_TAGS
#define MAX_TAGS                        32

#define NCR5380_implementation_fields   /* none */

#define NCR5380_read(reg)               atari_scsi_reg_read(reg)
#define NCR5380_write(reg, value)       atari_scsi_reg_write(reg, value)

#define NCR5380_queue_command           atari_scsi_queue_command
#define NCR5380_abort                   atari_scsi_abort
#define NCR5380_show_info               atari_scsi_show_info
#define NCR5380_info                    atari_scsi_info

#define NCR5380_dma_read_setup(instance, data, count) \
        atari_scsi_dma_setup(instance, data, count, 0)
#define NCR5380_dma_write_setup(instance, data, count) \
        atari_scsi_dma_setup(instance, data, count, 1)
#define NCR5380_dma_residual(instance) \
        atari_scsi_dma_residual(instance)
#define NCR5380_dma_xfer_len(instance, cmd, phase) \
        atari_dma_xfer_len(cmd->SCp.this_residual, cmd, !((phase) & SR_IO))

#define NCR5380_acquire_dma_irq(instance)      falcon_get_lock()
#define NCR5380_release_dma_irq(instance)      falcon_release_lock()

#include "NCR5380.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;
}

#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

#ifdef REAL_DMA
static void atari_scsi_fetch_restbytes(void);
#endif

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)
#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;

        dprintk(NDEBUG_INTR, "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);

                dprintk(NDEBUG_DMA, "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) {
                                dprintk(NDEBUG_DMA, "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);

        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;
                dprintk(NDEBUG_DMA, "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;
                dprintk(NDEBUG_DMA, "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);
                dprintk(NDEBUG_DMA, " = virt addr %p\n", dst);
                for (src = (char *)&tt_scsi_dma.dma_restdata; nr != 0; --nr)
                        *dst++ = *src++;
        }
}
#endif /* REAL_DMA */


/* This function releases the lock on the DMA chip if there is no
 * connected command and the disconnected queue is empty.
 */

static void falcon_release_lock(void)
{
        if (IS_A_TT())
                return;

        if (stdma_is_locked_by(scsi_falcon_intr))
                stdma_release();
}

/* 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 tell the SCSI mid-layer to defer.
 */

static int falcon_get_lock(void)
{
        if (IS_A_TT())
                return 1;

        if (in_interrupt())
                return stdma_try_lock(scsi_falcon_intr, NULL);

        stdma_lock(scsi_falcon_intr, NULL);
        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, 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)
                setup_can_queue = ints[1];
        if (ints[0] >= 2)
                setup_cmd_per_lun = ints[2];
        if (ints[0] >= 3)
                setup_sg_tablesize = ints[3];
        if (ints[0] >= 4)
                setup_hostid = ints[4];
#ifdef SUPPORT_TAGS
        if (ints[0] >= 5)
                setup_use_tagged_queuing = ints[5];
#endif

        return 1;
}

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


#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

#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);

        dprintk(NDEBUG_DMA, "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(struct 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,
                                        struct 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)
                dprintk(NDEBUG_DMA, "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 int atari_scsi_bus_reset(struct scsi_cmnd *cmd)
{
        int rv;
        unsigned long flags;

        local_irq_save(flags);

#ifdef REAL_DMA
        /* Abort a maybe active DMA transfer */
        if (IS_A_TT()) {
                tt_scsi_dma.dma_ctrl = 0;
        } else {
                st_dma.dma_mode_status = 0x90;
                atari_dma_active = 0;
                atari_dma_orig_addr = NULL;
        }
#endif

        rv = NCR5380_bus_reset(cmd);

        /* The 5380 raises its IRQ line while _RST is active but the ST DMA
         * "lock" has been released so this interrupt may end up handled by
         * floppy or IDE driver (if one of them holds the lock). The NCR5380
         * interrupt flag has been cleared already.
         */

        local_irq_restore(flags);

        return rv;
}

#define DRV_MODULE_NAME         "atari_scsi"
#define PFX                     DRV_MODULE_NAME ": "

static struct scsi_host_template atari_scsi_template = {
        .module                 = THIS_MODULE,
        .proc_name              = DRV_MODULE_NAME,
        .show_info              = atari_scsi_show_info,
        .name                   = "Atari native SCSI",
        .info                   = atari_scsi_info,
        .queuecommand           = atari_scsi_queue_command,
        .eh_abort_handler       = atari_scsi_abort,
        .eh_bus_reset_handler   = atari_scsi_bus_reset,
        .this_id                = 7,
        .use_clustering         = DISABLE_CLUSTERING
};

static int __init atari_scsi_probe(struct platform_device *pdev)
{
        struct Scsi_Host *instance;
        int error;
        struct resource *irq;
        int host_flags = 0;

        irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
        if (!irq)
                return -ENODEV;

        if (ATARIHW_PRESENT(TT_SCSI)) {
                atari_scsi_reg_read  = atari_scsi_tt_reg_read;
                atari_scsi_reg_write = atari_scsi_tt_reg_write;
        } else {
                atari_scsi_reg_read  = atari_scsi_falcon_reg_read;
                atari_scsi_reg_write = atari_scsi_falcon_reg_write;
        }

        /* The values for CMD_PER_LUN and CAN_QUEUE are somehow arbitrary.
         * Higher values should work, too; try it!
         * (But cmd_per_lun costs memory!)
         *
         * But there seems to be a bug somewhere that requires CAN_QUEUE to be
         * 2*CMD_PER_LUN. At least on a TT, no spurious timeouts seen since
         * changed CMD_PER_LUN...
         *
         * Note: The Falcon currently uses 8/1 setting due to unsolved problems
         * with cmd_per_lun != 1
         */
        if (ATARIHW_PRESENT(TT_SCSI)) {
                atari_scsi_template.can_queue    = 16;
                atari_scsi_template.cmd_per_lun  = 8;
                atari_scsi_template.sg_tablesize = SG_ALL;
        } else {
                atari_scsi_template.can_queue    = 8;
                atari_scsi_template.cmd_per_lun  = 1;
                atari_scsi_template.sg_tablesize = SG_NONE;
        }

        if (setup_can_queue > 0)
                atari_scsi_template.can_queue = setup_can_queue;

        if (setup_cmd_per_lun > 0)
                atari_scsi_template.cmd_per_lun = setup_cmd_per_lun;

        /* Leave sg_tablesize at 0 on a Falcon! */
        if (ATARIHW_PRESENT(TT_SCSI) && setup_sg_tablesize >= 0)
                atari_scsi_template.sg_tablesize = setup_sg_tablesize;

        if (setup_hostid >= 0) {
                atari_scsi_template.this_id = setup_hostid & 7;
        } else {
                /* 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)
                                atari_scsi_template.this_id = b & 7;
                }
        }

#ifdef SUPPORT_TAGS
        if (setup_use_tagged_queuing < 0)
                setup_use_tagged_queuing = 0;
#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 (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) {
                        pr_err(PFX "can't allocate ST-RAM double buffer\n");
                        return -ENOMEM;
                }
                atari_dma_phys_buffer = atari_stram_to_phys(atari_dma_buffer);
                atari_dma_orig_addr = 0;
        }
#endif

        instance = scsi_host_alloc(&atari_scsi_template,
                                   sizeof(struct NCR5380_hostdata));
        if (!instance) {
                error = -ENOMEM;
                goto fail_alloc;
        }
        atari_scsi_host = instance;

#ifdef CONFIG_ATARI_SCSI_RESET_BOOT
        atari_scsi_reset_boot();
#endif

        instance->irq = irq->start;

        host_flags |= IS_A_TT() ? 0 : FLAG_LATE_DMA_SETUP;

        NCR5380_init(instance, host_flags);

        if (IS_A_TT()) {
                error = request_irq(instance->irq, scsi_tt_intr, 0,
                                    "NCR5380", instance);
                if (error) {
                        pr_err(PFX "request irq %d failed, aborting\n",
                               instance->irq);
                        goto fail_irq;
                }
                tt_mfp.active_edge |= 0x80;     /* SCSI int on L->H */
#ifdef REAL_DMA
                tt_scsi_dma.dma_ctrl = 0;
                atari_dma_residual = 0;

                /* 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 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.
                 */
                if (MACH_IS_MEDUSA) {
                        struct NCR5380_hostdata *hostdata =
                                shost_priv(instance);

                        hostdata->read_overruns = 4;
                }
#endif
        } else {
                /* Nothing to do for the interrupt: the ST-DMA is initialized
                 * already.
                 */
#ifdef REAL_DMA
                atari_dma_residual = 0;
                atari_dma_active = 0;
                atari_dma_stram_mask = (ATARIHW_PRESENT(EXTD_DMA) ? 0x00000000
                                        : 0xff000000);
#endif
        }

        error = scsi_add_host(instance, NULL);
        if (error)
                goto fail_host;

        platform_set_drvdata(pdev, instance);

        scsi_scan_host(instance);
        return 0;

fail_host:
        if (IS_A_TT())
                free_irq(instance->irq, instance);
fail_irq:
        NCR5380_exit(instance);
        scsi_host_put(instance);
fail_alloc:
        if (atari_dma_buffer)
                atari_stram_free(atari_dma_buffer);
        return error;
}

static int __exit atari_scsi_remove(struct platform_device *pdev)
{
        struct Scsi_Host *instance = platform_get_drvdata(pdev);

        scsi_remove_host(instance);
        if (IS_A_TT())
                free_irq(instance->irq, instance);
        NCR5380_exit(instance);
        scsi_host_put(instance);
        if (atari_dma_buffer)
                atari_stram_free(atari_dma_buffer);
        return 0;
}

static struct platform_driver atari_scsi_driver = {
        .remove = __exit_p(atari_scsi_remove),
        .driver = {
                .name   = DRV_MODULE_NAME,
                .owner  = THIS_MODULE,
        },
};

module_platform_driver_probe(atari_scsi_driver, atari_scsi_probe);

MODULE_ALIAS("platform:" DRV_MODULE_NAME);
MODULE_LICENSE("GPL");