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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/x86/boot/video-bios.c
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// SPDX-License-Identifier: GPL-2.0-only

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/* -*- linux-c -*- ------------------------------------------------------- *

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 *

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 *   Copyright (C) 1991, 1992 Linus Torvalds

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 *   Copyright 2007 rPath, Inc. - All Rights Reserved

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 *   Copyright 2009 Intel Corporation; author H. Peter Anvin

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 *

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 * ----------------------------------------------------------------------- */

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/*

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 * Standard video BIOS modes

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 *

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 * We have two options for this; silent and scanned.

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 */

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#include "boot.h"

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#include "video.h"

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static __videocard video_bios;

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/* Set a conventional BIOS mode */

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static int set_bios_mode(u8 mode);

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static int bios_set_mode(struct mode_info *mi)

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{

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	return set_bios_mode(mi->mode - VIDEO_FIRST_BIOS);

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}

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static int set_bios_mode(u8 mode)

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{

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	struct biosregs ireg, oreg;

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	u8 new_mode;

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	initregs(&ireg);

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	ireg.al = mode;		/* AH=0x00 Set Video Mode */

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	intcall(0x10, &ireg, NULL);

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	ireg.ah = 0x0f;		/* Get Current Video Mode */

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	intcall(0x10, &ireg, &oreg);

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	do_restore = 1;		/* Assume video contents were lost */

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	/* Not all BIOSes are clean with the top bit */

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	new_mode = oreg.al & 0x7f;

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	if (new_mode == mode)

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		return 0;	/* Mode change OK */

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#ifndef _WAKEUP

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	if (new_mode != boot_params.screen_info.orig_video_mode) {

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		/* Mode setting failed, but we didn't end up where we

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		   started.  That's bad.  Try to revert to the original

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		   video mode. */

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		ireg.ax = boot_params.screen_info.orig_video_mode;

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		intcall(0x10, &ireg, NULL);

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	}

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#endif

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	return -1;

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}

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static int bios_probe(void)

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{

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	u8 mode;

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#ifdef _WAKEUP

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	u8 saved_mode = 0x03;

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#else

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	u8 saved_mode = boot_params.screen_info.orig_video_mode;

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#endif

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	u16 crtc;

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	struct mode_info *mi;

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	int nmodes = 0;

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	if (adapter != ADAPTER_EGA && adapter != ADAPTER_VGA)

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		return 0;

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	set_fs(0);

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	crtc = vga_crtc();

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

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	for (mode = 0x14; mode <= 0x7f; mode++) {

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		if (!heap_free(sizeof(struct mode_info)))

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			break;

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		if (mode_defined(VIDEO_FIRST_BIOS+mode))

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			continue;

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		if (set_bios_mode(mode))

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			continue;

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

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		/* Attribute Controller: make graphics controller disabled */

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		if (in_idx(0x3c0, 0x10) & 0x01)

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			continue;

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		/* Graphics Controller: verify Alpha addressing enabled */

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		if (in_idx(0x3ce, 0x06) & 0x01)

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			continue;

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		/* CRTC cursor location low should be zero(?) */

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		if (in_idx(crtc, 0x0f))

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			continue;

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		mi = GET_HEAP(struct mode_info, 1);

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		mi->mode = VIDEO_FIRST_BIOS+mode;

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		mi->depth = 0;	/* text */

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		mi->x = rdfs16(0x44a);

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		mi->y = rdfs8(0x484)+1;

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		nmodes++;

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	}

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	set_bios_mode(saved_mode);

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	return nmodes;

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}

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static __videocard video_bios =

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{

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	.card_name	= "BIOS",

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	.probe		= bios_probe,

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	.set_mode	= bios_set_mode,

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	.unsafe		= 1,

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	.xmode_first	= VIDEO_FIRST_BIOS,

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	.xmode_n	= 0x80,

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};

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