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edd.c

/* -*- linux-c -*- ------------------------------------------------------- *
 *
 *   Copyright (C) 1991, 1992 Linus Torvalds
 *   Copyright 2007 rPath, Inc. - All Rights Reserved
 *
 *   This file is part of the Linux kernel, and is made available under
 *   the terms of the GNU General Public License version 2.
 *
 * ----------------------------------------------------------------------- */

/*
 * arch/i386/boot/edd.c
 *
 * Get EDD BIOS disk information
 */

#include "boot.h"
#include <linux/edd.h>

#if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)

/*
 * Read the MBR (first sector) from a specific device.
 */
static int read_mbr(u8 devno, void *buf)
{
      u16 ax, bx, cx, dx;

      ax = 0x0201;            /* Legacy Read, one sector */
      cx = 0x0001;            /* Sector 0-0-1 */
      dx = devno;
      bx = (size_t)buf;
      asm volatile("pushfl; stc; int $0x13; setc %%al; popfl"
                 : "+a" (ax), "+c" (cx), "+d" (dx), "+b" (bx)
                 : : "esi", "edi", "memory");

      return -(u8)ax;         /* 0 or -1 */
}

static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)
{
      int sector_size;
      char *mbrbuf_ptr, *mbrbuf_end;
      u32 buf_base, mbr_base;
      extern char _end[];

      sector_size = ei->params.bytes_per_sector;
      if (!sector_size)
            sector_size = 512; /* Best available guess */

      /* Produce a naturally aligned buffer on the heap */
      buf_base = (ds() << 4) + (u32)&_end;
      mbr_base = (buf_base+sector_size-1) & ~(sector_size-1);
      mbrbuf_ptr = _end + (mbr_base-buf_base);
      mbrbuf_end = mbrbuf_ptr + sector_size;

      /* Make sure we actually have space on the heap... */
      if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))
            return -1;
      if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)
            return -1;

      if (read_mbr(devno, mbrbuf_ptr))
            return -1;

      *mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
      return 0;
}

static int get_edd_info(u8 devno, struct edd_info *ei)
{
      u16 ax, bx, cx, dx, di;

      memset(ei, 0, sizeof *ei);

      /* Check Extensions Present */

      ax = 0x4100;
      bx = EDDMAGIC1;
      dx = devno;
      asm("pushfl; stc; int $0x13; setc %%al; popfl"
          : "+a" (ax), "+b" (bx), "=c" (cx), "+d" (dx)
          : : "esi", "edi");

      if ((u8)ax)
            return -1;  /* No extended information */

      if (bx != EDDMAGIC2)
            return -1;

      ei->device  = devno;
      ei->version = ax >> 8;  /* EDD version number */
      ei->interface_support = cx; /* EDD functionality subsets */

      /* Extended Get Device Parameters */

      ei->params.length = sizeof(ei->params);
      ax = 0x4800;
      dx = devno;
      asm("pushfl; int $0x13; popfl"
          : "+a" (ax), "+d" (dx), "=m" (ei->params)
          : "S" (&ei->params)
          : "ebx", "ecx", "edi");

      /* Get legacy CHS parameters */

      /* Ralf Brown recommends setting ES:DI to 0:0 */
      ax = 0x0800;
      dx = devno;
      di = 0;
      asm("pushw %%es; "
          "movw %%di,%%es; "
          "pushfl; stc; int $0x13; setc %%al; popfl; "
          "popw %%es"
          : "+a" (ax), "=b" (bx), "=c" (cx), "+d" (dx), "+D" (di)
          : : "esi");

      if ((u8)ax == 0) {
            ei->legacy_max_cylinder = (cx >> 8) + ((cx & 0xc0) << 2);
            ei->legacy_max_head = dx >> 8;
            ei->legacy_sectors_per_track = cx & 0x3f;
      }

      return 0;
}

void query_edd(void)
{
      char eddarg[8];
      int do_mbr = 1;
      int do_edd = 1;
      int devno;
      struct edd_info ei, *edp;
      u32 *mbrptr;

      if (cmdline_find_option("edd", eddarg, sizeof eddarg) > 0) {
            if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip"))
                  do_mbr = 0;
            else if (!strcmp(eddarg, "off"))
                  do_edd = 0;
      }

      edp    = boot_params.eddbuf;
      mbrptr = boot_params.edd_mbr_sig_buffer;

      if (!do_edd)
            return;

      for (devno = 0x80; devno < 0x80+EDD_MBR_SIG_MAX; devno++) {
            /*
             * Scan the BIOS-supported hard disks and query EDD
             * information...
             */
            get_edd_info(devno, &ei);

            if (boot_params.eddbuf_entries < EDDMAXNR) {
                  memcpy(edp, &ei, sizeof ei);
                  edp++;
                  boot_params.eddbuf_entries++;
            }

            if (do_mbr && !read_mbr_sig(devno, &ei, mbrptr++))
                  boot_params.edd_mbr_sig_buf_entries = devno-0x80+1;
      }
}

#endif

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