grub/disk/ata.c

/* ata.c - ATA disk access.  */
/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 2007, 2008, 2009  Free Software Foundation, Inc.
 *
 *  GRUB is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  GRUB is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <grub/ata.h>
#include <grub/dl.h>
#include <grub/disk.h>
#include <grub/mm.h>
#include <grub/time.h>
#include <grub/pci.h>
#include <grub/scsi.h>

/* At the moment, only two IDE ports are supported.  */
static const int grub_ata_ioaddress[] = { 0x1f0, 0x170 };
static const int grub_ata_ioaddress2[] = { 0x3f6, 0x376 };

static struct grub_ata_device *grub_ata_devices;

/* Wait for !BSY.  */
grub_err_t
grub_ata_wait_not_busy (struct grub_ata_device *dev, int milliseconds)
{
  /* ATA requires 400ns (after a write to CMD register) or
     1 PIO cycle (after a DRQ block transfer) before
     first check of BSY.  */
  grub_millisleep (1);

  int i = 1;
  while (grub_ata_regget (dev, GRUB_ATA_REG_STATUS) & GRUB_ATA_STATUS_BUSY)
    {
      if (i >= milliseconds)
        {
	  grub_dprintf ("ata", "timeout: %dms\n", milliseconds);
	  return grub_error (GRUB_ERR_TIMEOUT, "ATA timeout");
	}

      grub_millisleep (1);
      i++;
    }

  return GRUB_ERR_NONE;
}

static inline void
grub_ata_wait (void)
{
  grub_millisleep (50);
}

/* Wait for !BSY, DRQ.  */
grub_err_t
grub_ata_wait_drq (struct grub_ata_device *dev, int rw,
		   int milliseconds)
{
  if (grub_ata_wait_not_busy (dev, milliseconds))
    return grub_errno;

  /* !DRQ implies error condition.  */
  grub_uint8_t sts = grub_ata_regget (dev, GRUB_ATA_REG_STATUS);
  if ((sts & (GRUB_ATA_STATUS_DRQ | GRUB_ATA_STATUS_ERR))
      != GRUB_ATA_STATUS_DRQ)
    {
      grub_dprintf ("ata", "ata error: status=0x%x, error=0x%x\n",
		    sts, grub_ata_regget (dev, GRUB_ATA_REG_ERROR));
      if (! rw)
        return grub_error (GRUB_ERR_READ_ERROR, "ATA read error");
      else
        return grub_error (GRUB_ERR_WRITE_ERROR, "ATA write error");
    }

  return GRUB_ERR_NONE;
}

/* Byteorder has to be changed before strings can be read.  */
static void
grub_ata_strncpy (char *dst, char *src, grub_size_t len)
{
  grub_uint16_t *src16 = (grub_uint16_t *) src;
  grub_uint16_t *dst16 = (grub_uint16_t *) dst;
  unsigned int i;

  for (i = 0; i < len / 2; i++)
    *(dst16++) = grub_be_to_cpu16 (*(src16++));
  dst[len] = '\0';
}

void
grub_ata_pio_read (struct grub_ata_device *dev, char *buf, grub_size_t size)
{
  grub_uint16_t *buf16 = (grub_uint16_t *) buf;
  unsigned int i;

  /* Read in the data, word by word.  */
  for (i = 0; i < size / 2; i++)
    buf16[i] = grub_le_to_cpu16 (grub_inw(dev->ioaddress + GRUB_ATA_REG_DATA));
}

static void
grub_ata_pio_write (struct grub_ata_device *dev, char *buf, grub_size_t size)
{
  grub_uint16_t *buf16 = (grub_uint16_t *) buf;
  unsigned int i;

  /* Write the data, word by word.  */
  for (i = 0; i < size / 2; i++)
    grub_outw(grub_cpu_to_le16 (buf16[i]), dev->ioaddress + GRUB_ATA_REG_DATA);
}

static void
grub_ata_dumpinfo (struct grub_ata_device *dev, char *info)
{
  char text[41];

  /* The device information was read, dump it for debugging.  */
  grub_ata_strncpy (text, info + 20, 20);
  grub_dprintf ("ata", "Serial: %s\n", text);
  grub_ata_strncpy (text, info + 46, 8);
  grub_dprintf ("ata", "Firmware: %s\n", text);
  grub_ata_strncpy (text, info + 54, 40);
  grub_dprintf ("ata", "Model: %s\n", text);

  if (! dev->atapi)
    {
      grub_dprintf ("ata", "Addressing: %d\n", dev->addr);
      grub_dprintf ("ata", "Sectors: %lld\n", dev->size);
    }
}

static grub_err_t
grub_atapi_identify (struct grub_ata_device *dev)
{
  char *info;

  info = grub_malloc (GRUB_DISK_SECTOR_SIZE);
  if (! info)
    return grub_errno;

  grub_ata_regset (dev, GRUB_ATA_REG_DISK, 0xE0 | dev->device << 4);
  if (grub_ata_check_ready (dev))
    {
      grub_free (info);
      return grub_errno;
    }

  grub_ata_regset (dev, GRUB_ATA_REG_CMD, GRUB_ATA_CMD_IDENTIFY_PACKET_DEVICE);
  grub_ata_wait ();

  if (grub_ata_wait_drq (dev, 0, GRUB_ATA_TOUT_STD))
    {
      grub_free (info);
      return grub_errno;
    }
  grub_ata_pio_read (dev, info, GRUB_DISK_SECTOR_SIZE);

  dev->atapi = 1;

  grub_ata_dumpinfo (dev, info);

  grub_free (info);

  return GRUB_ERR_NONE;
}

static grub_err_t
grub_atapi_wait_drq (struct grub_ata_device *dev,
		     grub_uint8_t ireason,
		     int milliseconds)
{
  /* Wait for !BSY, DRQ, ireason */
  if (grub_ata_wait_not_busy (dev, milliseconds))
    return grub_errno;

  grub_uint8_t sts = grub_ata_regget (dev, GRUB_ATA_REG_STATUS);
  grub_uint8_t irs = grub_ata_regget (dev, GRUB_ATAPI_REG_IREASON);

  /* OK if DRQ is asserted and interrupt reason is as expected.  */
  if ((sts & GRUB_ATA_STATUS_DRQ)
      && (irs & GRUB_ATAPI_IREASON_MASK) == ireason)
    return GRUB_ERR_NONE;

  /* !DRQ implies error condition.  */
  grub_dprintf ("ata", "atapi error: status=0x%x, ireason=0x%x, error=0x%x\n",
	        sts, irs, grub_ata_regget (dev, GRUB_ATA_REG_ERROR));

  if (! (sts & GRUB_ATA_STATUS_DRQ)
      && (irs & GRUB_ATAPI_IREASON_MASK) == GRUB_ATAPI_IREASON_ERROR)
    {
      if (ireason == GRUB_ATAPI_IREASON_CMD_OUT)
	return grub_error (GRUB_ERR_READ_ERROR, "ATA PACKET command error");
      else
	return grub_error (GRUB_ERR_READ_ERROR, "ATAPI read error");
    }

  return grub_error (GRUB_ERR_READ_ERROR, "ATAPI protocol error");
}

static grub_err_t
grub_atapi_packet (struct grub_ata_device *dev, char *packet,
		   grub_size_t size)
{
  grub_ata_regset (dev, GRUB_ATA_REG_DISK, dev->device << 4);
  if (grub_ata_check_ready (dev))
    return grub_errno;

  /* Send ATA PACKET command.  */
  grub_ata_regset (dev, GRUB_ATA_REG_FEATURES, 0);
  grub_ata_regset (dev, GRUB_ATAPI_REG_IREASON, 0);
  grub_ata_regset (dev, GRUB_ATAPI_REG_CNTHIGH, size >> 8);
  grub_ata_regset (dev, GRUB_ATAPI_REG_CNTLOW, size & 0xFF);

  grub_ata_regset (dev, GRUB_ATA_REG_CMD, GRUB_ATA_CMD_PACKET);

  /* Wait for !BSY, DRQ, !I/O, C/D.  */
  if (grub_atapi_wait_drq (dev, GRUB_ATAPI_IREASON_CMD_OUT, GRUB_ATA_TOUT_STD))
    return grub_errno;

  /* Write the packet.  */
  grub_ata_pio_write (dev, packet, 12);

  return GRUB_ERR_NONE;
}

static grub_err_t
grub_ata_identify (struct grub_ata_device *dev)
{
  char *info;
  grub_uint16_t *info16;

  info = grub_malloc (GRUB_DISK_SECTOR_SIZE);
  if (! info)
    return grub_errno;

  info16 = (grub_uint16_t *) info;

  grub_ata_regset (dev, GRUB_ATA_REG_DISK, 0xE0 | dev->device << 4);
  if (grub_ata_check_ready (dev))
    {
      grub_free (info);
      return grub_errno;
    }

  grub_ata_regset (dev, GRUB_ATA_REG_CMD, GRUB_ATA_CMD_IDENTIFY_DEVICE);
  grub_ata_wait ();

  if (grub_ata_wait_drq (dev, 0, GRUB_ATA_TOUT_STD))
    {
      if (grub_ata_regget (dev, GRUB_ATA_REG_ERROR) & 0x04) /* ABRT */
	{
	  /* Device without ATA IDENTIFY, try ATAPI.  */
	  grub_free(info);
	  grub_errno = GRUB_ERR_NONE;
	  return grub_atapi_identify (dev);
	}
      else
	{
	  /* Error.  */
	  grub_free(info);
	  return grub_error (GRUB_ERR_UNKNOWN_DEVICE,
			     "device can not be identified");
	}
    }

  grub_ata_pio_read (dev, info, GRUB_DISK_SECTOR_SIZE);

  /* Now it is certain that this is not an ATAPI device.  */
  dev->atapi = 0;

  /* CHS is always supported.  */
  dev->addr = GRUB_ATA_CHS;

  /* Check if LBA is supported.  */
  if (info16[49] & (1 << 9))
    {
      /* Check if LBA48 is supported.  */
      if (info16[83] & (1 << 10))
	dev->addr = GRUB_ATA_LBA48;
      else
	dev->addr = GRUB_ATA_LBA;
    }

  /* Determine the amount of sectors.  */
  if (dev->addr != GRUB_ATA_LBA48)
    dev->size = grub_le_to_cpu32(*((grub_uint32_t *) &info16[60]));
  else
    dev->size = grub_le_to_cpu64(*((grub_uint64_t *) &info16[100]));

  /* Read CHS information.  */
  dev->cylinders = info16[1];
  dev->heads = info16[3];
  dev->sectors_per_track = info16[6];

  grub_ata_dumpinfo (dev, info);

  grub_free(info);

  return 0;
}

static grub_err_t
grub_ata_device_initialize (int port, int device, int addr, int addr2)
{
  struct grub_ata_device *dev;
  struct grub_ata_device **devp;

  grub_dprintf ("ata", "detecting device %d,%d (0x%x, 0x%x)\n",
		port, device, addr, addr2);

  dev = grub_malloc (sizeof(*dev));
  if (! dev)
    return grub_errno;

  /* Setup the device information.  */
  dev->port = port;
  dev->device = device;
  dev->ioaddress = addr;
  dev->ioaddress2 = addr2;
  dev->next = NULL;

  grub_ata_regset (dev, GRUB_ATA_REG_DISK, dev->device << 4);
  grub_ata_wait ();

  /* If status is 0x00, it is safe to assume that there
     is no device (or only a !READY) device connected.  */
  grub_int8_t sts = grub_ata_regget (dev, GRUB_ATA_REG_STATUS);
  grub_dprintf ("ata", "status=0x%x\n", sts);
  if (sts == 0x00)
    {
      grub_free(dev);
      return 0;
    }

  /* Try to detect if the port is in use by writing to it,
     waiting for a while and reading it again.  If the value
     was preserved, there is a device connected.
     But this tests often detects a second (slave) device
     connected to a SATA controller which supports only one
     (master) device.  In this case, the status register
     check above usually works.  */
  grub_ata_regset (dev, GRUB_ATA_REG_SECTORS, 0x5A);  
  grub_ata_wait ();
  grub_int8_t sec = grub_ata_regget (dev, GRUB_ATA_REG_SECTORS);
  grub_dprintf ("ata", "sectors=0x%x\n", sec);
  if (sec != 0x5A)
    {
      grub_free(dev);
      return 0;
    }

  /* Use the IDENTIFY DEVICE command to query the device.  */
  if (grub_ata_identify (dev))
    {
      grub_free (dev);
      return 0;
    }

  /* Register the device.  */
  for (devp = &grub_ata_devices; *devp; devp = &(*devp)->next);
  *devp = dev;

  return 0;
}

static int NESTED_FUNC_ATTR
grub_ata_pciinit (int bus, int device, int func,
		  grub_pci_id_t pciid __attribute__((unused)))
{
  static int compat_use[2] = { 0 };
  grub_pci_address_t addr;
  grub_uint32_t class;
  grub_uint32_t bar1;
  grub_uint32_t bar2;
  int rega;
  int regb;
  int i;
  static int controller = 0;

  /* Read class.  */
  addr = grub_pci_make_address (bus, device, func, 2);
  class = grub_pci_read (addr);

  /* Check if this class ID matches that of a PCI IDE Controller.  */
  if (class >> 16 != 0x0101)
    return 0;

  for (i = 0; i < 2; i++)
    {
      /* Set to 0 when the channel operated in compatibility mode.  */
      int compat = (class >> (8 + 2 * i)) & 1;

      rega = 0;
      regb = 0;

      /* If the channel is in compatibility mode, just assign the
	 default registers.  */
      if (compat == 0 && !compat_use[i])
	{
	  rega = grub_ata_ioaddress[i];
	  regb = grub_ata_ioaddress2[i];
	  compat_use[i] = 1;
	}
      else if (compat)
	{
	  /* Read the BARs, which either contain a mmapped IO address
	     or the IO port address.  */
	  addr = grub_pci_make_address (bus, device, func, 4 + 2 * i);
	  bar1 = grub_pci_read (addr);
	  addr = grub_pci_make_address (bus, device, func, 5 + 2 * i);
	  bar2 = grub_pci_read (addr);

	  /* Check if the BARs describe an IO region.  */
	  if ((bar1 & 1) && (bar2 & 1))   
	    {
	      rega = bar1 & ~3;
	      regb = bar2 & ~3;
	    }
	}

      grub_dprintf ("ata",
		    "PCI dev (%d,%d,%d) compat=%d rega=0x%x regb=0x%x\n",
		    bus, device, func, compat, rega, regb);

      if (rega && regb)
	{
	  grub_errno = GRUB_ERR_NONE;
	  grub_ata_device_initialize (controller * 2 + i, 0, rega, regb);

	  /* Most errors raised by grub_ata_device_initialize() are harmless.
	     They just indicate this particular drive is not responding, most
	     likely because it doesn't exist.  We might want to ignore specific
	     error types here, instead of printing them.  */
	  if (grub_errno)
	    {
	      grub_print_error ();
	      grub_errno = GRUB_ERR_NONE;
	    }

	  grub_ata_device_initialize (controller * 2 + i, 1, rega, regb);

	  /* Likewise.  */
	  if (grub_errno)
	    {
	      grub_print_error ();
	      grub_errno = GRUB_ERR_NONE;
	    }
	}
    }

  controller++;

  return 0;
}

static grub_err_t
grub_ata_initialize (void)
{
  grub_pci_iterate (grub_ata_pciinit);
  return 0;
}


static void
grub_ata_setlba (struct grub_ata_device *dev, grub_disk_addr_t sector,
		 grub_size_t size)
{
  grub_ata_regset (dev, GRUB_ATA_REG_SECTORS, size);
  grub_ata_regset (dev, GRUB_ATA_REG_LBALOW, sector & 0xFF);
  grub_ata_regset (dev, GRUB_ATA_REG_LBAMID, (sector >> 8) & 0xFF);
  grub_ata_regset (dev, GRUB_ATA_REG_LBAHIGH, (sector >> 16) & 0xFF);
}

static grub_err_t
grub_ata_setaddress (struct grub_ata_device *dev,
		     grub_ata_addressing_t addressing,
		     grub_disk_addr_t sector,
		     grub_size_t size)
{
  switch (addressing)
    {
    case GRUB_ATA_CHS:
      {
	unsigned int cylinder;
	unsigned int head;
	unsigned int sect;

	/* Calculate the sector, cylinder and head to use.  */
	sect = ((grub_uint32_t) sector % dev->sectors_per_track) + 1;
	cylinder = (((grub_uint32_t) sector / dev->sectors_per_track)
		    / dev->heads);
	head = ((grub_uint32_t) sector / dev->sectors_per_track) % dev->heads;

	if (sect > dev->sectors_per_track
	    || cylinder > dev->cylinders
	    || head > dev->heads)
	  return grub_error (GRUB_ERR_OUT_OF_RANGE,
			     "sector %d can not be addressed "
			     "using CHS addressing", sector);

	grub_ata_regset (dev, GRUB_ATA_REG_DISK, (dev->device << 4) | head);
	if (grub_ata_check_ready (dev))
	  return grub_errno;

	grub_ata_regset (dev, GRUB_ATA_REG_SECTNUM, sect);
	grub_ata_regset (dev, GRUB_ATA_REG_CYLLSB, cylinder & 0xFF);
	grub_ata_regset (dev, GRUB_ATA_REG_CYLMSB, cylinder >> 8);

	break;
      }

    case GRUB_ATA_LBA:
      if (size == 256)
	size = 0;
      grub_ata_regset (dev, GRUB_ATA_REG_DISK,
		       0xE0 | (dev->device << 4) | ((sector >> 24) & 0x0F));
      if (grub_ata_check_ready (dev))
	return grub_errno;

      grub_ata_setlba (dev, sector, size);
      break;

    case GRUB_ATA_LBA48:
      if (size == 65536)
	size = 0;

      grub_ata_regset (dev, GRUB_ATA_REG_DISK, 0xE0 | (dev->device << 4));
      if (grub_ata_check_ready (dev))
	return grub_errno;

      /* Set "Previous".  */
      grub_ata_setlba (dev, sector >> 24, size >> 8);
      /* Set "Current".  */
      grub_ata_setlba (dev, sector, size);

      break;
    }

  return GRUB_ERR_NONE;
}

static grub_err_t
grub_ata_readwrite (grub_disk_t disk, grub_disk_addr_t sector,
		    grub_size_t size, char *buf, int rw)
{
  struct grub_ata_device *dev = (struct grub_ata_device *) disk->data;

  grub_dprintf("ata", "grub_ata_readwrite (size=%u, rw=%d)\n", size, rw);

  grub_ata_addressing_t addressing = dev->addr;
  grub_size_t batch;
  int cmd, cmd_write;

  if (addressing == GRUB_ATA_LBA48 && ((sector + size) >> 28) != 0)
    {
      batch = 65536;
      cmd = GRUB_ATA_CMD_READ_SECTORS_EXT;
      cmd_write = GRUB_ATA_CMD_WRITE_SECTORS_EXT;
    }
  else
    {
      if (addressing == GRUB_ATA_LBA48)
	addressing = GRUB_ATA_LBA;
      batch = 256;
      cmd = GRUB_ATA_CMD_READ_SECTORS;
      cmd_write = GRUB_ATA_CMD_WRITE_SECTORS;
    }

  grub_size_t nsectors = 0;
  while (nsectors < size)
    {
      if (size - nsectors < batch)
	batch = size - nsectors;

      grub_dprintf("ata", "rw=%d, sector=%llu, batch=%u\n", rw, sector, batch);

      /* Send read/write command.  */
      if (grub_ata_setaddress (dev, addressing, sector, batch))
	return grub_errno;

      grub_ata_regset (dev, GRUB_ATA_REG_CMD, (! rw ? cmd : cmd_write));

      unsigned sect;
      for (sect = 0; sect < batch; sect++)
	{
	  /* Wait for !BSY, DRQ.  */
	  if (grub_ata_wait_drq (dev, rw, GRUB_ATA_TOUT_DATA))
	    return grub_errno;

	  /* Transfer data.  */
	  if (! rw)
	    grub_ata_pio_read (dev, buf, GRUB_DISK_SECTOR_SIZE);
	  else
	    grub_ata_pio_write (dev, buf, GRUB_DISK_SECTOR_SIZE);

	  buf += GRUB_DISK_SECTOR_SIZE;
	}

      if (rw)
        {
	  /* Check for write error.  */
	  if (grub_ata_wait_not_busy (dev, GRUB_ATA_TOUT_DATA))
	    return grub_errno;

	  if (grub_ata_regget (dev, GRUB_ATA_REG_STATUS)
	      & (GRUB_ATA_STATUS_DRQ | GRUB_ATA_STATUS_ERR))
	    return grub_error (GRUB_ERR_WRITE_ERROR, "ATA write error");
	}

      sector += batch;
      nsectors += batch;
    }

  return GRUB_ERR_NONE;
}



static int
grub_ata_iterate (int (*hook) (const char *name))
{
  struct grub_ata_device *dev;

  for (dev = grub_ata_devices; dev; dev = dev->next)
    {
      char devname[5];
      grub_sprintf (devname, "ata%d", dev->port * 2 + dev->device);

      if (dev->atapi)
	continue;

      if (hook (devname))
	return 1;
    }

  return 0;
}

static grub_err_t
grub_ata_open (const char *name, grub_disk_t disk)
{
  struct grub_ata_device *dev;

  for (dev = grub_ata_devices; dev; dev = dev->next)
    {
      char devname[5];
      grub_sprintf (devname, "ata%d", dev->port * 2 + dev->device);
      if (grub_strcmp (name, devname) == 0)
	break;
    }

  if (! dev)
    return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "Can't open device");

  if (dev->atapi)
    return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "not an ATA harddisk");

  disk->total_sectors = dev->size;

  disk->id = (unsigned long) dev;
  
  disk->has_partitions = 1;
  disk->data = dev;

  return 0;
}

static void
grub_ata_close (grub_disk_t disk __attribute__((unused)))
{
  
}

static grub_err_t
grub_ata_read (grub_disk_t disk, grub_disk_addr_t sector,
	       grub_size_t size, char *buf)
{
  return grub_ata_readwrite (disk, sector, size, buf, 0);
}

static grub_err_t
grub_ata_write (grub_disk_t disk,
		grub_disk_addr_t sector,
		grub_size_t size,
		const char *buf)
{
  return grub_ata_readwrite (disk, sector, size, (char *) buf, 1);
}

static struct grub_disk_dev grub_atadisk_dev =
  {
    .name = "ATA",
    .id = GRUB_DISK_DEVICE_ATA_ID,
    .iterate = grub_ata_iterate,
    .open = grub_ata_open,
    .close = grub_ata_close,
    .read = grub_ata_read,
    .write = grub_ata_write,
    .next = 0
  };



/* ATAPI code.  */

static int
grub_atapi_iterate (int (*hook) (const char *name, int luns))
{
  struct grub_ata_device *dev;

  for (dev = grub_ata_devices; dev; dev = dev->next)
    {
      char devname[7];
      grub_sprintf (devname, "ata%d", dev->port * 2 + dev->device);

      if (! dev->atapi)
	continue;

      if (hook (devname, 1))
	return 1;
    }

  return 0;

}

static grub_err_t
grub_atapi_read (struct grub_scsi *scsi,
		 grub_size_t cmdsize __attribute__((unused)),
		 char *cmd, grub_size_t size, char *buf)
{
  struct grub_ata_device *dev = (struct grub_ata_device *) scsi->data;

  grub_dprintf("ata", "grub_atapi_read (size=%u)\n", size);

  if (grub_atapi_packet (dev, cmd, size))
    return grub_errno;

  grub_size_t nread = 0;
  while (nread < size)
    {
      /* Wait for !BSY, DRQ, I/O, !C/D.  */
      if (grub_atapi_wait_drq (dev, GRUB_ATAPI_IREASON_DATA_IN, GRUB_ATA_TOUT_DATA))
	return grub_errno;

      /* Get byte count for this DRQ assertion.  */
      unsigned cnt = grub_ata_regget (dev, GRUB_ATAPI_REG_CNTHIGH) << 8
		   | grub_ata_regget (dev, GRUB_ATAPI_REG_CNTLOW);
      grub_dprintf("ata", "DRQ count=%u\n", cnt);

      /* Count of last transfer may be uneven.  */
      if (! (0 < cnt && cnt <= size - nread && (! (cnt & 1) || cnt == size - nread)))
	return grub_error (GRUB_ERR_READ_ERROR, "Invalid ATAPI transfer count");

      /* Read the data.  */
      grub_ata_pio_read (dev, buf + nread, cnt);

      if (cnt & 1)
	buf[nread + cnt - 1] = (char) grub_le_to_cpu16 (grub_inw (dev->ioaddress + GRUB_ATA_REG_DATA));

      nread += cnt;
    }

  return GRUB_ERR_NONE;
}

static grub_err_t
grub_atapi_write (struct grub_scsi *scsi __attribute__((unused)),
		  grub_size_t cmdsize __attribute__((unused)),
		  char *cmd __attribute__((unused)),
		  grub_size_t size __attribute__((unused)),
		  char *buf __attribute__((unused)))
{
  // XXX: scsi.mod does not use write yet.
  return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET, "ATAPI write not implemented");
}

static grub_err_t
grub_atapi_open (const char *name, struct grub_scsi *scsi)
{
  struct grub_ata_device *dev;
  struct grub_ata_device *devfnd = 0;

  for (dev = grub_ata_devices; dev; dev = dev->next)
    {
      char devname[7];
      grub_sprintf (devname, "ata%d", dev->port * 2 + dev->device);

      if (!grub_strcmp (devname, name))
	{
	  devfnd = dev;
	  break;
	}
    }

  grub_dprintf ("ata", "opening ATAPI dev `%s'\n", name);

  if (! devfnd)
    return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "No such ATAPI device");

  scsi->data = devfnd;

  return GRUB_ERR_NONE;
}

static void
grub_atapi_close (struct grub_scsi *scsi)
{
  grub_free (scsi->name);
}

static struct grub_scsi_dev grub_atapi_dev =
  {
    .name = "ATAPI",
    .iterate = grub_atapi_iterate,
    .open = grub_atapi_open,
    .close = grub_atapi_close,
    .read = grub_atapi_read,
    .write = grub_atapi_write
  }; 



GRUB_MOD_INIT(ata)
{
  /* To prevent two drivers operating on the same disks.  */
  grub_disk_firmware_is_tainted = 1;
  if (grub_disk_firmware_fini)
    {
      grub_disk_firmware_fini ();
      grub_disk_firmware_fini = NULL;
    }
  
  /* ATA initialization.  */
  grub_ata_initialize ();

  grub_disk_dev_register (&grub_atadisk_dev);

  /* ATAPI devices are handled by scsi.mod.  */
  grub_scsi_dev_register (&grub_atapi_dev);
}

GRUB_MOD_FINI(ata)
{
  grub_scsi_dev_unregister (&grub_atapi_dev);
  grub_disk_dev_unregister (&grub_atadisk_dev);
}