kernel/arch/x86/boot/video-mode.c

// SPDX-License-Identifier: GPL-2.0-only
/* -*- linux-c -*- ------------------------------------------------------- *
 *
 *   Copyright (C) 1991, 1992 Linus Torvalds
 *   Copyright 2007-2008 rPath, Inc. - All Rights Reserved
 *
 * ----------------------------------------------------------------------- */

/*
 * arch/i386/boot/video-mode.c
 *
 * Set the video mode.  This is separated out into a different
 * file in order to be shared with the ACPI wakeup code.
 */

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

#include <uapi/asm/boot.h>

/*
 * Common variables
 */
int adapter;		/* 0=CGA/MDA/HGC, 1=EGA, 2=VGA+ */
int force_x, force_y;	/* Don't query the BIOS for cols/rows */
int do_restore;		/* Screen contents changed during mode flip */
int graphic_mode;	/* Graphic mode with linear frame buffer */

/* Probe the video drivers and have them generate their mode lists. */
void probe_cards(int unsafe)
{
	struct card_info *card;
	static u8 probed[2];

	if (probed[unsafe])
		return;

	probed[unsafe] = 1;

	for (card = video_cards; card < video_cards_end; card++) {
		if (card->unsafe == unsafe) {
			if (card->probe)
				card->nmodes = card->probe();
			else
				card->nmodes = 0;
		}
	}
}

/* Test if a mode is defined */
int mode_defined(u16 mode)
{
	struct card_info *card;
	struct mode_info *mi;
	int i;

	for (card = video_cards; card < video_cards_end; card++) {
		mi = card->modes;
		for (i = 0; i < card->nmodes; i++, mi++) {
			if (mi->mode == mode)
				return 1;
		}
	}

	return 0;
}

/* Set mode (without recalc) */
static int raw_set_mode(u16 mode, u16 *real_mode)
{
	int nmode, i;
	struct card_info *card;
	struct mode_info *mi;

	/* Drop the recalc bit if set */
	mode &= ~VIDEO_RECALC;

	/* Scan for mode based on fixed ID, position, or resolution */
	nmode = 0;
	for (card = video_cards; card < video_cards_end; card++) {
		mi = card->modes;
		for (i = 0; i < card->nmodes; i++, mi++) {
			int visible = mi->x || mi->y;

			if ((mode == nmode && visible) ||
			    mode == mi->mode ||
			    mode == (mi->y << 8)+mi->x) {
				*real_mode = mi->mode;
				return card->set_mode(mi);
			}

			if (visible)
				nmode++;
		}
	}

	/* Nothing found?  Is it an "exceptional" (unprobed) mode? */
	for (card = video_cards; card < video_cards_end; card++) {
		if (mode >= card->xmode_first &&
		    mode < card->xmode_first+card->xmode_n) {
			struct mode_info mix;
			*real_mode = mix.mode = mode;
			mix.x = mix.y = 0;
			return card->set_mode(&mix);
		}
	}

	/* Otherwise, failure... */
	return -1;
}

/*
 * Recalculate the vertical video cutoff (hack!)
 */
static void vga_recalc_vertical(void)
{
	unsigned int font_size, rows;
	u16 crtc;
	u8 pt, ov;

	set_fs(0);
	font_size = rdfs8(0x485); /* BIOS: font size (pixels) */
	rows = force_y ? force_y : rdfs8(0x484)+1; /* Text rows */

	rows *= font_size;	/* Visible scan lines */
	rows--;			/* ... minus one */

	crtc = vga_crtc();

	pt = in_idx(crtc, 0x11);
	pt &= ~0x80;		/* Unlock CR0-7 */
	out_idx(pt, crtc, 0x11);

	out_idx((u8)rows, crtc, 0x12); /* Lower height register */

	ov = in_idx(crtc, 0x07); /* Overflow register */
	ov &= 0xbd;
	ov |= (rows >> (8-1)) & 0x02;
	ov |= (rows >> (9-6)) & 0x40;
	out_idx(ov, crtc, 0x07);
}

/* Set mode (with recalc if specified) */
int set_mode(u16 mode)
{
	int rv;
	u16 real_mode;

	/* Very special mode numbers... */
	if (mode == VIDEO_CURRENT_MODE)
		return 0;	/* Nothing to do... */
	else if (mode == NORMAL_VGA)
		mode = VIDEO_80x25;
	else if (mode == EXTENDED_VGA)
		mode = VIDEO_8POINT;

	rv = raw_set_mode(mode, &real_mode);
	if (rv)
		return rv;

	if (mode & VIDEO_RECALC)
		vga_recalc_vertical();

	/* Save the canonical mode number for the kernel, not
	   an alias, size specification or menu position */
#ifndef _WAKEUP
	boot_params.hdr.vid_mode = real_mode;
#endif
	return 0;
}