Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 892 insertions, 0 deletions

diff --git a/drivers/scsi/atari_scsi.c b/drivers/scsi/atari_scsi.c
new file mode 100644
index 0000000000..d401cf2711
--- /dev/null
+++ b/drivers/scsi/atari_scsi.c
@@ -0,0 +1,892 @@
+/*
+ * 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 DMA
+ *
+ * The 5380 device is one of several that all share the DMA chip. Hence
+ * "locking" and "unlocking" access to this chip is required.
+ *
+ * Two possible schemes for ST DMA acquisition by atari_scsi are:
+ * 1) The lock is taken for each command separately (i.e. can_queue == 1).
+ * 2) The lock is taken when the first command arrives and released
+ * when the last command is finished (i.e. can_queue > 1).
+ *
+ * The first alternative limits SCSI bus utilization, since interleaving
+ * commands is not possible. The second gives better performance but is
+ * unfair to other drivers needing to use the ST DMA chip. In order to
+ * allow the IDE and floppy drivers equal access to the ST DMA chip
+ * the default is can_queue == 1.
+ */
+
+#include <linux/module.h>
+#include <linux/types.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>
+
+#define DMA_MIN_SIZE                    32
+
+/* Definitions for the core NCR5380 driver. */
+
+#define NCR5380_implementation_fields   /* none */
+
+static u8 (*atari_scsi_reg_read)(unsigned int);
+static void (*atari_scsi_reg_write)(unsigned int, u8);
+
+#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_info                    atari_scsi_info
+
+#define NCR5380_dma_xfer_len            atari_scsi_dma_xfer_len
+#define NCR5380_dma_recv_setup          atari_scsi_dma_recv_setup
+#define NCR5380_dma_send_setup          atari_scsi_dma_send_setup
+#define NCR5380_dma_residual            atari_scsi_dma_residual
+
+#define NCR5380_acquire_dma_irq(instance)      falcon_get_lock(instance)
+#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;
+}
+
+static void atari_scsi_fetch_restbytes(void);
+
+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)
+
+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);
+static int setup_hostid = -1;
+module_param(setup_hostid, int, 0);
+static int setup_toshiba_delay = -1;
+module_param(setup_toshiba_delay, int, 0);
+
+
+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;
+}
+
+
+static irqreturn_t scsi_tt_intr(int irq, void *dev)
+{
+	struct Scsi_Host *instance = dev;
+	struct NCR5380_hostdata *hostdata = shost_priv(instance);
+	int dma_stat;
+
+	dma_stat = tt_scsi_dma.dma_ctrl;
+
+	dsprintk(NDEBUG_INTR, instance, "NCR5380 interrupt, DMA status = %02x\n",
+	         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->dma_len -
+			(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;
+	}
+
+	NCR5380_intr(irq, dev);
+
+	return IRQ_HANDLED;
+}
+
+
+static irqreturn_t scsi_falcon_intr(int irq, void *dev)
+{
+	struct Scsi_Host *instance = dev;
+	struct NCR5380_hostdata *hostdata = shost_priv(instance);
+	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->dma_len - 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->dma_len - atari_dma_residual);
+		atari_dma_orig_addr = NULL;
+	}
+
+	NCR5380_intr(irq, dev);
+
+	return IRQ_HANDLED;
+}
+
+
+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++;
+	}
+}
+
+
+/* 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(struct Scsi_Host *instance)
+{
+	if (IS_A_TT())
+		return 1;
+
+	if (stdma_is_locked_by(scsi_falcon_intr))
+		return 1;
+
+	/* stdma_lock() may sleep which means it can't be used here */
+	return stdma_try_lock(scsi_falcon_intr, instance);
+}
+
+#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[8];
+
+	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];
+	/* ints[5] (use_tagged_queuing) is ignored */
+	/* ints[6] (use_pdma) is ignored */
+	if (ints[0] >= 7)
+		setup_toshiba_delay = ints[7];
+
+	return 1;
+}
+
+__setup("atascsi=", atari_scsi_setup);
+#endif /* !MODULE */
+
+static unsigned long atari_scsi_dma_setup(struct NCR5380_hostdata *hostdata,
+					  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",
+	        hostdata->host->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 (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 inline int atari_scsi_dma_recv_setup(struct NCR5380_hostdata *hostdata,
+                                            unsigned char *data, int count)
+{
+	return atari_scsi_dma_setup(hostdata, data, count, 0);
+}
+
+static inline int atari_scsi_dma_send_setup(struct NCR5380_hostdata *hostdata,
+                                            unsigned char *data, int count)
+{
+	return atari_scsi_dma_setup(hostdata, data, count, 1);
+}
+
+static int atari_scsi_dma_residual(struct NCR5380_hostdata *hostdata)
+{
+	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 int atari_scsi_dma_xfer_len(struct NCR5380_hostdata *hostdata,
+                                   struct scsi_cmnd *cmd)
+{
+	int wanted_len = NCR5380_to_ncmd(cmd)->this_residual;
+	int possible_len, limit;
+
+	if (wanted_len < DMA_MIN_SIZE)
+		return 0;
+
+	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 (cmd->sc_data_direction == DMA_TO_DEVICE) {
+		/* 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(NCR5380_to_ncmd(cmd)->ptr))) ?
+		    STRAM_BUFFER_SIZE : 255*512;
+	if (possible_len > limit)
+		possible_len = limit;
+
+	if (possible_len != wanted_len)
+		dprintk(NDEBUG_DMA, "DMA transfer now %d bytes instead of %d\n",
+		        possible_len, wanted_len);
+
+	return possible_len;
+}
+
+
+/* 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 u8 atari_scsi_tt_reg_read(unsigned int reg)
+{
+	return tt_scsi_regp[reg * 2];
+}
+
+static void atari_scsi_tt_reg_write(unsigned int reg, u8 value)
+{
+	tt_scsi_regp[reg * 2] = value;
+}
+
+static u8 atari_scsi_falcon_reg_read(unsigned int reg)
+{
+	unsigned long flags;
+	u8 result;
+
+	reg += 0x88;
+	local_irq_save(flags);
+	dma_wd.dma_mode_status = (u_short)reg;
+	result = (u8)dma_wd.fdc_acces_seccount;
+	local_irq_restore(flags);
+	return result;
+}
+
+static void atari_scsi_falcon_reg_write(unsigned int reg, u8 value)
+{
+	unsigned long flags;
+
+	reg += 0x88;
+	local_irq_save(flags);
+	dma_wd.dma_mode_status = (u_short)reg;
+	dma_wd.fdc_acces_seccount = (u_short)value;
+	local_irq_restore(flags);
+}
+
+
+#include "NCR5380.c"
+
+static int atari_scsi_host_reset(struct scsi_cmnd *cmd)
+{
+	int rv;
+	unsigned long flags;
+
+	local_irq_save(flags);
+
+	/* Abort a maybe active DMA transfer */
+	if (IS_A_TT()) {
+		tt_scsi_dma.dma_ctrl = 0;
+	} else {
+		if (stdma_is_locked_by(scsi_falcon_intr))
+			st_dma.dma_mode_status = 0x90;
+		atari_dma_active = 0;
+		atari_dma_orig_addr = NULL;
+	}
+
+	rv = NCR5380_host_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,
+	.name			= "Atari native SCSI",
+	.info			= atari_scsi_info,
+	.queuecommand		= atari_scsi_queue_command,
+	.eh_abort_handler	= atari_scsi_abort,
+	.eh_host_reset_handler	= atari_scsi_host_reset,
+	.this_id		= 7,
+	.cmd_per_lun		= 2,
+	.dma_boundary		= PAGE_SIZE - 1,
+	.cmd_size		= sizeof(struct NCR5380_cmd),
+};
+
+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;
+	}
+
+	if (ATARIHW_PRESENT(TT_SCSI)) {
+		atari_scsi_template.can_queue    = 16;
+		atari_scsi_template.sg_tablesize = SG_ALL;
+	} else {
+		atari_scsi_template.can_queue    = 1;
+		atari_scsi_template.sg_tablesize = 1;
+	}
+
+	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;
+
+	/* Don't increase sg_tablesize on 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 if (IS_REACHABLE(CONFIG_NVRAM)) {
+		/* Test if a host id is set in the NVRam */
+		if (ATARIHW_PRESENT(TT_CLK)) {
+			unsigned char b;
+			loff_t offset = 16;
+			ssize_t count = nvram_read(&b, 1, &offset);
+
+			/* Arbitration enabled? (for TOS)
+			 * If yes, use configured host ID
+			 */
+			if ((count == 1) && (b & 0x80))
+				atari_scsi_template.this_id = b & 7;
+		}
+	}
+
+	/* 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_realnum_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 = NULL;
+	}
+
+	instance = scsi_host_alloc(&atari_scsi_template,
+	                           sizeof(struct NCR5380_hostdata));
+	if (!instance) {
+		error = -ENOMEM;
+		goto fail_alloc;
+	}
+
+	instance->irq = irq->start;
+
+	host_flags |= IS_A_TT() ? 0 : FLAG_LATE_DMA_SETUP;
+	host_flags |= setup_toshiba_delay > 0 ? FLAG_TOSHIBA_DELAY : 0;
+
+	error = NCR5380_init(instance, host_flags);
+	if (error)
+		goto fail_init;
+
+	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 */
+
+		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;
+		}
+	} else {
+		/* Nothing to do for the interrupt: the ST-DMA is initialized
+		 * already.
+		 */
+		atari_dma_residual = 0;
+		atari_dma_active = 0;
+		atari_dma_stram_mask = (ATARIHW_PRESENT(EXTD_DMA) ? 0x00000000
+					: 0xff000000);
+	}
+
+	NCR5380_maybe_reset_bus(instance);
+
+	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);
+fail_init:
+	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,
+	},
+};
+
+module_platform_driver_probe(atari_scsi_driver, atari_scsi_probe);
+
+MODULE_ALIAS("platform:" DRV_MODULE_NAME);
+MODULE_LICENSE("GPL");