root/arch/x86/boot/edd.c

DEFINITIONS

1. read_mbr
2. read_mbr_sig
3. get_edd_info
4. query_edd

/* -*- 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.
 *
 * ----------------------------------------------------------------------- */

/*
 * 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[];
        u16 mbr_magic;

        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;

        memset(mbrbuf_ptr, 0, sector_size);
        if (read_mbr(devno, mbrbuf_ptr))
                return -1;

        *mbrsig = *(u32 *)&mbrbuf_ptr[EDD_MBR_SIG_OFFSET];
        mbr_magic = *(u16 *)&mbrbuf_ptr[510];

        /* check for valid MBR magic */
        return mbr_magic == 0xAA55 ? 0 : -1;
}

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;
#ifdef CONFIG_EDD_OFF
        int do_edd = 0;
#else
        int do_edd = 1;
#endif
        int be_quiet;
        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_edd = 1;
                        do_mbr = 0;
                }
                else if (!strcmp(eddarg, "off"))
                        do_edd = 0;
                else if (!strcmp(eddarg, "on"))
                        do_edd = 1;
        }

        be_quiet = cmdline_find_option_bool("quiet");

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

        if (!do_edd)
                return;

        /* Bugs in OnBoard or AddOnCards Bios may hang the EDD probe,
         * so give a hint if this happens.
         */

        if (!be_quiet)
                printf("Probing EDD (edd=off to disable)... ");

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

        if (!be_quiet)
                printf("ok\n");
}

#endif