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video-bios.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/video-bios.c
 *
 * Standard video BIOS modes
 *
 * We have two options for this; silent and scanned.
 */

#include "boot.h"
#include "video.h"

__videocard video_bios;

/* Set a conventional BIOS mode */
static int set_bios_mode(u8 mode);

static int bios_set_mode(struct mode_info *mi)
{
      return set_bios_mode(mi->mode - VIDEO_FIRST_BIOS);
}

static int set_bios_mode(u8 mode)
{
      u16 ax;
      u8 new_mode;

      ax = mode;        /* AH=0x00 Set Video Mode */
      asm volatile(INT10
                 : "+a" (ax)
                 : : "ebx", "ecx", "edx", "esi", "edi");

      ax = 0x0f00;            /* Get Current Video Mode */
      asm volatile(INT10
                 : "+a" (ax)
                 : : "ebx", "ecx", "edx", "esi", "edi");

      do_restore = 1;         /* Assume video contents were lost */
      new_mode = ax & 0x7f;   /* Not all BIOSes are clean with the top bit */

      if (new_mode == mode)
            return 0;   /* Mode change OK */

      if (new_mode != boot_params.screen_info.orig_video_mode) {
            /* Mode setting failed, but we didn't end up where we
               started.  That's bad.  Try to revert to the original
               video mode. */
            ax = boot_params.screen_info.orig_video_mode;
            asm volatile(INT10
                       : "+a" (ax)
                       : : "ebx", "ecx", "edx", "esi", "edi");
      }
      return -1;
}

static int bios_probe(void)
{
      u8 mode;
      u8 saved_mode = boot_params.screen_info.orig_video_mode;
      u16 crtc;
      struct mode_info *mi;
      int nmodes = 0;

      if (adapter != ADAPTER_EGA && adapter != ADAPTER_VGA)
            return 0;

      set_fs(0);
      crtc = vga_crtc();

      video_bios.modes = GET_HEAP(struct mode_info, 0);

      for (mode = 0x14; mode <= 0x7f; mode++) {
            if (!heap_free(sizeof(struct mode_info)))
                  break;

            if (mode_defined(VIDEO_FIRST_BIOS+mode))
                  continue;

            if (set_bios_mode(mode))
                  continue;

            /* Try to verify that it's a text mode. */

            /* Attribute Controller: make graphics controller disabled */
            if (in_idx(0x3c0, 0x10) & 0x01)
                  continue;

            /* Graphics Controller: verify Alpha addressing enabled */
            if (in_idx(0x3ce, 0x06) & 0x01)
                  continue;

            /* CRTC cursor location low should be zero(?) */
            if (in_idx(crtc, 0x0f))
                  continue;

            mi = GET_HEAP(struct mode_info, 1);
            mi->mode = VIDEO_FIRST_BIOS+mode;
            mi->x = rdfs16(0x44a);
            mi->y = rdfs8(0x484)+1;
            nmodes++;
      }

      set_bios_mode(saved_mode);

      return nmodes;
}

__videocard video_bios =
{
      .card_name  = "BIOS (scanned)",
      .probe            = bios_probe,
      .set_mode   = bios_set_mode,
      .unsafe           = 1,
      .xmode_first      = VIDEO_FIRST_BIOS,
      .xmode_n    = 0x80,
};

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