edd.c

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/* -*- linux-c -*- ------------------------------------------------------- *
 *
 *   Copyright (C) 1991, 1992 Linus Torvalds
 *   Copyright 2007 rPath, Inc. - All Rights Reserved
 *   Copyright 2009 Intel Corporation; author H. Peter Anvin
 *
 *   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)
{
    struct biosregs ireg, oreg;

    initregs(&ireg);
    ireg.ax = 0x0201;       /* Legacy Read, one sector */
    ireg.cx = 0x0001;       /* Sector 0-0-1 */
    ireg.dl = devno;
    ireg.bx = (size_t)buf;

    intcall(0x13, &ireg, &oreg);

    return -(oreg.eflags & X86_EFLAGS_CF); /* 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)
{
    struct biosregs ireg, oreg;

    memset(ei, 0, sizeof *ei);

    /* Check Extensions Present */

    initregs(&ireg);
    ireg.ah = 0x41;
    ireg.bx = EDDMAGIC1;
    ireg.dl = devno;
    intcall(0x13, &ireg, &oreg);

    if (oreg.eflags & X86_EFLAGS_CF)
        return -1;  /* No extended information */

    if (oreg.bx != EDDMAGIC2)
        return -1;

    ei->device  = devno;
    ei->version = oreg.ah;       /* EDD version number */
    ei->interface_support = oreg.cx; /* EDD functionality subsets */

    /* Extended Get Device Parameters */

    ei->params.length = sizeof(ei->params);
    ireg.ah = 0x48;
    ireg.si = (size_t)&ei->params;
    intcall(0x13, &ireg, &oreg);

    /* Get legacy CHS parameters */

    /* Ralf Brown recommends setting ES:DI to 0:0 */
    ireg.ah = 0x08;
    ireg.es = 0;
    intcall(0x13, &ireg, &oreg);

    if (!(oreg.eflags & X86_EFLAGS_CF)) {
        ei->legacy_max_cylinder = oreg.ch + ((oreg.cl & 0xc0) << 2);
        ei->legacy_max_head = oreg.dh;
        ei->legacy_sectors_per_track = oreg.cl & 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