/* Copyright (C) 1991, 1992 Aladdin Enterprises.  All rights reserved.

This file is part of Ghostscript.

Ghostscript is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY.  No author or distributor accepts responsibility
to anyone for the consequences of using it or for whether it serves any
particular purpose or works at all, unless he says so in writing.  Refer
to the Ghostscript General Public License for full details.

Everyone is granted permission to copy, modify and redistribute
Ghostscript, but only under the conditions described in the Ghostscript
General Public License.  A copy of this license is supposed to have been
given to you along with Ghostscript so you can know your rights and
responsibilities.  It should be in a file named COPYING.  Among other
things, the copyright notice and this notice must be preserved on all
copies.  */

/* gdevsvga.c */
/* SuperVGA display drivers for Ghostscript */
#include "memory_.h"
#include "gx.h"
#include "gserrors.h"
#include "gxdevice.h"
#include "gdevpcfb.h"
#include "gdevsvga.h"

/* The color map for dynamically assignable colors. */
#define first_dc_index 64
private int next_dc_index;
#define dc_hash_size 293	/* prime, >num_dc */
typedef struct { ushort rgb, index; } dc_entry;
private dc_entry dynamic_colors[dc_hash_size + 1];

/* Macro for casting gx_device argument */
#define fb_dev ((gx_device_svga *)dev)

/* Procedure records */
#define svga_procs(open) {\
	open, gx_default_get_initial_matrix,\
	gx_default_sync_output, gx_default_output_page, svga_close,\
	svga_map_rgb_color, svga_map_color_rgb,\
	svga_fill_rectangle, gx_default_tile_rectangle,\
	svga_copy_mono, svga_copy_color, gx_default_draw_line,\
	svga_get_bits, gx_default_get_props, gx_default_put_props\
}

/* Save the controller mode */
private int svga_save_mode = -1;

/* ------ Internal routines ------ */

#define regen 0xa000

/* Construct a pointer for writing a pixel. */
/* Assume 64K pages, 64K granularity. */
/* We know that y is within bounds. */
#define set_pixel_ptr(ptr, fbdev, x, y, wnum)\
{	ulong index = (ulong)(y) * fbdev->raster + (uint)(x);\
	if ( (uint)(index >> 16) != fbdev->page )\
	   {	(*fbdev->set_page)(fbdev, (fbdev->page = index >> 16), wnum);\
	   }\
	ptr = (fb_ptr)MK_PTR(regen, (ushort)index);\
}
#define set_pixel_write_ptr(ptr, fbdev, x, y)\
  set_pixel_ptr(ptr, fbdev, x, y, fbdev->wnum_write)
#define set_pixel_read_ptr(ptr, fbdev, x, y)\
  set_pixel_ptr(ptr, fbdev, x, y, fbdev->wnum_read)

/* Find the graphics mode for a desired width and height. */
/* Set the mode in the device structure and return 0, */
/* or return an error code. */
int
svga_find_mode(gx_device *dev, const mode_info _ds *mip)
{	for ( ; ; mip++ )
	{	if ( mip->width >= fb_dev->width &&
		     mip->height >= fb_dev->height ||
		     mip[1].mode < 0
		   )
		{	fb_dev->mode = mip;
			gx_device_adjust_resolution(dev, mip->width, mip->height, 1);
			fb_dev->raster = fb_dev->width;
			return 0;
		}
	}
	return_error(gs_error_rangecheck);
}

/* Set the index for writing into the color DAC. */
#define svga_dac_set_write_index(i) outportb(0x3c8, i)

/* Write 6-bit R,G,B values into the color DAC. */
#define svga_dac_write(r, g, b)\
  (outportb(0x3c9, r), outportb(0x3c9, g), outportb(0x3c9, b))

/* ------ Common procedures ------ */

/* Initialize the device structure and the DACs. */
int
svga_open(gx_device *dev)
{	fb_dev->x_pixels_per_inch =
	  fb_dev->y_pixels_per_inch =
	    fb_dev->height / PAGE_HEIGHT_INCHES;
	/* Set the display mode. */
	if ( svga_save_mode < 0 )
		svga_save_mode = (*fb_dev->get_mode)();
	(*fb_dev->set_mode)(fb_dev->mode->mode);
	/* Load the color DAC. */
	svga_dac_set_write_index(0);
	   {	int c;
		for ( c = 0; c < 64; c++ )
		   {	static const byte c2[10] =
			   { 0, 42, 0, 0, 0, 0, 0, 0, 21, 63 };
			svga_dac_write(c2[(c >> 2) & 9], c2[(c >> 1) & 9],
				       c2[c & 9]);
		   }
	   }
	/* Initialize the dynamic color table. */
	memset(dynamic_colors, 0, (dc_hash_size + 1) * sizeof(dc_entry));
	next_dc_index = first_dc_index;
	fb_dev->page = -1;
	return 0;
}

/* Close the device; reinitialize the display for text mode. */
int
svga_close(gx_device *dev)
{	if ( svga_save_mode >= 0 )
		(*fb_dev->set_mode)(svga_save_mode);
	svga_save_mode = -1;
	return 0;
}

/* Map a r-g-b color to a palette index. */
/* The first 64 entries of the color map are set */
/* for compatibility with the older display modes: */
/* these are indexed as 0.0.R0.G0.B0.R1.G1.B1. */
gx_color_index
svga_map_rgb_color(gx_device *dev, ushort r, ushort g, ushort b)
{
#define cv_bits(v,n) (v >> (gx_color_value_bits - n))
	ushort r5 = cv_bits(r, 5), g5 = cv_bits(g, 5), b5 = cv_bits(b, 5);
	static const byte cube_bits[32] =
	   {	0, 128, 128, 128, 128, 128, 128, 128, 128, 128,
		8, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128,
		1, 128, 128, 128, 128, 128, 128, 128, 128, 128,
		9
	   };
	uint cx = ((uint)cube_bits[r5] << 2) + ((uint)cube_bits[g5] << 1) +
		  (uint)cube_bits[b5];
	ushort rgb;
	register dc_entry _ds *pdc;
	/* Check for a color on the cube. */
	if ( cx < 64 ) return (gx_color_index)cx;
	/* Not on the cube, check the dynamic color table. */
	rgb = (r5 << 10) + (g5 << 5) + b5;
	for ( pdc = &dynamic_colors[rgb % dc_hash_size]; pdc->rgb != 0; pdc++ )
	{	if ( pdc->rgb == rgb )
			return (gx_color_index)(pdc->index);
	}
	if ( pdc == &dynamic_colors[dc_hash_size] )
	{	/* Wraparound */
		for ( pdc = &dynamic_colors[0]; pdc->rgb != 0; pdc++ )
		{	if ( pdc->rgb == rgb )
				return (gx_color_index)(pdc->index);
		}
	}
	if ( next_dc_index == 256 )
	{	/* No space left, report failure. */
		return gx_no_color_index;
	}
	/* Not on the cube, and not in the dynamic table. */
	/* Put in the dynamic table if space available. */
	{	int i = next_dc_index++;
		pdc->rgb = rgb;
		pdc->index = i;
		svga_dac_set_write_index(i);
		svga_dac_write(cv_bits(r, 6), cv_bits(g, 6), cv_bits(b, 6));
		return (gx_color_index)i;
	}
}

/* Map a color code to r-g-b. */
/* This routine must invert the transformation of the one above. */
/* Since this is practically never used, we just read the DAC. */
int
svga_map_color_rgb(gx_device *dev, gx_color_index color, ushort prgb[3])
{	uint cval;
	outportb(0x3c7, (byte)color);
#define dacin() (cval = inportb(0x3c9) >> 1,\
  ((cval << 11) + (cval << 6) + (cval << 1) + (cval >> 4)) >>\
   (16 - gx_color_value_bits))
	prgb[0] = dacin();
	prgb[1] = dacin();
	prgb[2] = dacin();
#undef dacin
	return 0;
}

/* Copy a monochrome bitmap.  The colors are given explicitly. */
/* Color = gx_no_color_index means transparent (no effect on the image). */
int
svga_copy_mono(gx_device *dev,
  const byte *base, int sourcex, int sraster, gx_bitmap_id id,
  int x, int y, int w, int h, gx_color_index czero, gx_color_index cone)
{	uint raster = fb_dev->raster;
	ushort limit;
	register int wi;
	uint skip;
	int yi;
	register fb_ptr ptr = (fb_ptr)0;
	const byte *srow;
	uint invert;
	fit_copy(dev, base, sourcex, sraster, id, x, y, w, h);
	limit = (ushort)-w;
	skip = raster - w + 1;
	srow = base + (sourcex >> 3);
#define izero (int)czero
#define ione (int)cone
	if ( ione == no_color )
	{	gx_color_index temp;
		if ( izero == no_color ) return 0;	/* no-op */
		temp = czero;
		czero = cone;
		cone = temp;
		invert = ~0;
	}
	else
		invert = 0;
	/* Pre-filling saves us a test in the loop, */
	/* and since tiling is uncommon, we come out ahead. */
	if ( izero != no_color )
		svga_fill_rectangle(dev, x, y, w, h, czero);
	for ( yi = 0; yi < h; yi++ )
	   {	const byte *sptr = srow;
		uint bits;
		int bitno = sourcex & 7;
		wi = w;
		if ( PTR_OFF(ptr) <= skip )
		{	set_pixel_write_ptr(ptr, fb_dev, x, y + yi);
		}
		else if ( PTR_OFF(ptr) > limit )
		{	/* We're crossing a page boundary. */
			/* This is extremely rare, so it doesn't matter */
			/* how slow it is. */
			int xi = (ushort)-PTR_OFF(ptr);
			svga_copy_mono(dev, srow, sourcex & 7, sraster,
				gx_no_bitmap_id, x, y + yi, xi, 1,
				gx_no_color_index, cone);
			set_pixel_write_ptr(ptr, fb_dev, x + xi, y + yi);
			sptr = srow - (sourcex >> 3) + ((sourcex + xi) >> 3);
			bitno = (sourcex + xi) & 7;
			wi -= xi;
		}
		bits = *sptr ^ invert;
		switch ( bitno )
		{
#define ifbit(msk)\
  if ( bits & msk ) *ptr = (byte)ione;\
  if ( !--wi ) break; ptr++
		case 0:
bit0:			ifbit(0x80);
		case 1:
			ifbit(0x40);
		case 2:
			ifbit(0x20);
		case 3:
			ifbit(0x10);
		case 4:
			ifbit(0x08);
		case 5:
			ifbit(0x04);
		case 6:
			ifbit(0x02);
		case 7:
			ifbit(0x01);
#undef ifbit
			bits = *++sptr ^ invert;
			goto bit0;
		}
		ptr += skip;
		srow += sraster;
	   }
#undef izero
#undef ione
	return 0;
}

/* Copy a color pixelmap.  This is just like a bitmap, */
/* except that each pixel takes 8 bits instead of 1. */
int
svga_copy_color(gx_device *dev,
  const byte *base, int sourcex, int sraster, gx_bitmap_id id,
  int x, int y, int w, int h)
{	int xi, yi;
	int skip;
	const byte *sptr;
	fb_ptr ptr;
	fit_copy(dev, base, sourcex, sraster, id, x, y, w, h);
	skip = sraster - w;
	sptr = base + sourcex;
	for ( yi = y; yi - y < h; yi++ )
	   {	ptr = 0;
		for ( xi = x; xi - x < w; xi++ )
		   {	if ( PTR_OFF(ptr) == 0 )
				set_pixel_write_ptr(ptr, fb_dev, xi, yi);
			*ptr++ = *sptr++;
		   }
		sptr += skip;
	   }
	return 0;
}

/* Fill a rectangle. */
int
svga_fill_rectangle(gx_device *dev, int x, int y, int w, int h,
  gx_color_index color)
{	uint raster = fb_dev->raster;
	ushort limit = (ushort)-raster;
	int yi;
	fb_ptr ptr;
	fit_fill(dev, x, y, w, h);
	set_pixel_write_ptr(ptr, fb_dev, x, y);
	/* Most fills are very small and don't cross a page boundary. */
	yi = h;
	switch ( w )
	   {
	case 0: return 0;		/* no-op */
	case 1:
		while ( --yi >= 0 && PTR_OFF(ptr) < limit )
			ptr[0] = (byte)color,
			ptr += raster;
		if ( !++yi ) return 0;
		break;
	case 2:
		while ( --yi >= 0 && PTR_OFF(ptr) < limit )
			ptr[0] = ptr[1] = (byte)color,
			ptr += raster;
		if ( !++yi ) return 0;
		break;
	case 3:
		while ( --yi >= 0 && PTR_OFF(ptr) < limit )
			ptr[0] = ptr[1] = ptr[2] = (byte)color,
			ptr += raster;
		if ( !++yi ) return 0;
		break;
	case 4:
		while ( --yi >= 0 && PTR_OFF(ptr) < limit )
			ptr[0] = ptr[1] = ptr[2] = ptr[3] = (byte)color,
			ptr += raster;
		if ( !++yi ) return 0;
		break;
	default:
		if ( w < 0 ) return 0;
	   }
	while ( --yi >= 0 )
	   {	if ( PTR_OFF(ptr) < limit )
		   {	memset(ptr, (byte)color, w);
			ptr += raster;
		   }
		else if ( PTR_OFF(ptr) <= (ushort)(-w) )
		   {	memset(ptr, (byte)color, w);
			if ( yi > 0 )
				set_pixel_write_ptr(ptr, fb_dev, x, y + h - yi);
		   }
		else
		   {	uint left = (uint)0x10000 - PTR_OFF(ptr);
			memset(ptr, (byte)color, left);
			set_pixel_write_ptr(ptr, fb_dev, x + left, y + h - 1 - yi);
			memset(ptr, (byte)color, w - left);
			ptr += raster - left;
		   }
	   }
	return 0;
}

/* Read scan lines back from the frame buffer. */
int
svga_get_bits(gx_device *dev, int y, byte *data, byte **actual_data)
{	uint bytes_per_row = dev->width;
	byte *dest = data;
	ushort limit = (ushort)-bytes_per_row;
	fb_ptr src;
	if ( y < 0 || y >= dev->height )
		return gs_error_rangecheck;
	set_pixel_read_ptr(src, fb_dev, 0, y);
	/* The logic here is similar to fill_rectangle. */
	if ( PTR_OFF(src) <= limit )
		memcpy(data, src, bytes_per_row);
	else
	   {	uint left = (uint)0x10000 - PTR_OFF(src);
		memcpy(data, src, left);
		set_pixel_read_ptr(src, fb_dev, left, y);
		memcpy(data + left, src, bytes_per_row - left);
	   }
	if ( actual_data != 0 )
		*actual_data = data;
	return 0;
}

/* ------ The VESA device ------ */

private dev_proc_open_device(vesa_open);
private gx_device_procs vesa_procs = svga_procs(vesa_open);
int vesa_get_mode(P0());
void vesa_set_mode(P1(int));
private void vesa_set_page(P3(gx_device_svga *, int, int));
gx_device_svga gs_vesa_device =
	svga_device(vesa_procs, "vesa", vesa_get_mode, vesa_set_mode, vesa_set_page);

/* Define the structures for information returned by the BIOS. */
#define bits_include(a, m) !(~(a) & (m))
/* Information about the BIOS capabilities. */
typedef struct {
	byte vesa_signature[4];		/* "VESA" */
	ushort vesa_version;
	char *product_info;		/* product name string */
	byte capabilities[4];		/* (undefined) */
	ushort *mode_list;		/* supported video modes, -1 ends */
} vga_bios_info;
/* Information about an individual VESA mode. */
typedef enum {
	m_supported = 1,
	m_graphics = 0x10
} mode_attribute;
typedef enum {
	w_supported = 1,
	w_readable = 2,
	w_writable = 4
} win_attribute;
typedef struct {
	ushort mode_attributes;
	byte win_a_attributes;
	byte win_b_attributes;
	ushort win_granularity;
	ushort win_size;
	ushort win_a_segment;
	ushort win_b_segment;
	void (*win_func_ptr)(P2(int, int));
	ushort bytes_per_line;
		/* Optional information */
	ushort x_resolution;
	ushort y_resolution;
	byte x_char_size;
	byte y_char_size;
	byte number_of_planes;
	byte bits_per_pixel;
	byte number_of_banks;
	byte memory_model;
	byte bank_size;
		/* Padding to 256 bytes */
	byte _padding[256-29];
} vesa_info;

/* Read the device mode */
int
vesa_get_mode(void)
{	registers regs;
	regs.h.ah = 0x4f;
	regs.h.al = 0x03;
	int86(0x10, &regs, &regs);
	return regs.rshort.bx;
}

/* Set the device mode */
void
vesa_set_mode(int mode)
{	registers regs;
	regs.h.ah = 0x4f;
	regs.h.al = 0x02;
	regs.rshort.bx = mode;
	int86(0x10, &regs, &regs);
}

/* Read information about a device mode */
private int
vesa_get_info(int mode, vesa_info _ss *info)
{	registers regs;
	struct SREGS sregs;
	regs.h.ah = 0x4f;
	regs.h.al = 0x01;
	regs.rshort.cx = mode;
	segread(&sregs);
	sregs.es = sregs.ss;
	regs.rshort.di = PTR_OFF(info);
	int86x(0x10, &regs, &regs, &sregs);
#ifdef DEBUG
	if ( regs.h.ah == 0 && regs.h.al == 0x4f )
		dprintf8("vesa_get_info(%x): ma=%x wa=%x/%x wg=%x ws=%x wseg=%x/%x\n",
			 mode, info->mode_attributes,
			 info->win_a_attributes, info->win_b_attributes,
			 info->win_granularity, info->win_size,
			 info->win_a_segment, info->win_b_segment);
	else
		dprintf3("vesa_get_info(%x) failed: ah=%x al=%x\n",
			 mode, regs.h.ah, regs.h.al);
#endif
	return (regs.h.ah == 0 && regs.h.al == 0x4f ? 0 : -1);
}

/* Initialize the graphics mode. */
/* Shared routine to look up a VESA-compatible BIOS mode. */
private int
vesa_find_mode(gx_device *dev, const mode_info _ds *mode_table)
{	/* Select the proper video mode */
	vesa_info info;
	const mode_info _ds *mip;
	for ( mip = mode_table; mip->mode >= 0; mip++ )
	   {	if ( mip->width >= fb_dev->width &&
		     mip->height >= fb_dev->height &&
		     vesa_get_info(mip->mode, &info) >= 0 &&
		     bits_include(info.mode_attributes,
			m_supported | m_graphics) &&
		     info.win_granularity == 64 &&
		     info.win_size == 64 &&
		     bits_include(info.win_a_attributes,
			w_supported) &&
		     info.win_a_segment == regen
		   )
		   {	/* Make sure we can both read & write. */
			/* Initialize for the default case. */
			fb_dev->wnum_read = 0;
			fb_dev->wnum_write = 0;
			if ( bits_include(info.win_a_attributes,
				w_readable | w_writable)
			   )
				break;
			else if ( info.win_b_segment == regen &&
				bits_include(info.win_b_attributes,
					w_supported) &&
				bits_include(info.win_a_attributes |
					info.win_b_attributes,
					w_readable | w_writable)
			   )
			   {	/* Two superimposed windows. */
				if ( !bits_include(info.win_a_attributes,
					w_writable)
				   )
					fb_dev->wnum_write = 1;
				else
					fb_dev->wnum_read = 1;
			   }
			break;
		   }
	   }
	if ( mip->mode < 0 )
		return_error(gs_error_rangecheck);	/* mode not available */
	fb_dev->mode = mip;
	gx_device_adjust_resolution(dev, mip->width, mip->height, 1);
	fb_dev->info.vesa.bios_set_page = info.win_func_ptr;
	/* Reset the raster per the VESA info. */
	fb_dev->raster = info.bytes_per_line;
	return 0;
}
private int
vesa_open(gx_device *dev)
{	static const mode_info mode_table[] = {
	   {	 640,  400, 0x100	},
	   {	 640,  480, 0x101	},
	   {	 800,  600, 0x103	},
	   {	1024,  768, 0x105	},
	   {	1280, 1024, 0x107	},
	   {	-1, -1, -1	}
	};
	int code = vesa_find_mode(dev, mode_table);
	if ( code < 0 ) return code;
	return svga_open(dev);
}

/* Set the current display page. */
private void
vesa_set_page(gx_device_svga *dev, int pn, int wnum)
{
#if USE_ASM
extern void vesa_call_set_page(P3(void (*)(P2(int, int)), int, int));
	if ( dev->info.vesa.bios_set_page != NULL )
		vesa_call_set_page(dev->info.vesa.bios_set_page, pn, wnum);
	else
#endif
	   {	registers regs;
		regs.rshort.dx = pn;
		regs.h.ah = 0x4f;
		regs.h.al = 5;
		regs.rshort.bx = wnum;
		int86(0x10, &regs, &regs);
	   }
}

/* ------ The ATI Wonder device ------ */

private dev_proc_open_device(atiw_open);
private gx_device_procs atiw_procs = svga_procs(atiw_open);
private int atiw_get_mode(P0());
private void atiw_set_mode(P1(int));
private void atiw_set_page(P3(gx_device_svga *, int, int));
gx_device_svga gs_atiw_device =
	svga_device(atiw_procs, "atiw", atiw_get_mode, atiw_set_mode, atiw_set_page);

/* Read the device mode */
private int
atiw_get_mode(void)
{	registers regs;
	regs.h.ah = 0xf;
	int86(0x10, &regs, &regs);
	return regs.h.al;
}

/* Set the device mode */
private void
atiw_set_mode(int mode)
{	registers regs;
	regs.h.ah = 0;
	regs.h.al = mode;
	int86(0x10, &regs, &regs);
}

/* Initialize the graphics mode. */
private int
atiw_open(gx_device *dev)
{	/* Select the proper video mode */
	   {	static const mode_info mode_table[] = {
		   {	 640,  400, 0x61	},
		   {	 640,  480, 0x62	},
		   {	 800,  600, 0x63	},
		   {	1024,  768, 0x64	},
		   {	-1, -1, -1	}
		};
		int code = svga_find_mode(dev, mode_table);
		if ( code < 0 ) return code;	/* mode not available */
		fb_dev->info.atiw.select_reg = *(int *)MK_PTR(0xc000, 0x10);
		return svga_open(dev);
	   }
}

/* Set the current display page. */
private void
atiw_set_page(gx_device_svga *dev, int pn, int wnum)
{	int select_reg = dev->info.atiw.select_reg;
	byte reg;
	disable();
	outportb(select_reg, 0xb2);
	reg = inportb(select_reg + 1);
	outportb(select_reg, 0xb2);
	outportb(select_reg + 1, (reg & 0xe1) + (pn << 1));
	enable();
}

/* ------ The Trident device ------ */

private dev_proc_open_device(tvga_open);
private gx_device_procs tvga_procs = svga_procs(tvga_open);
/* We can use the tseng_get/set_mode procedures. */
private void tvga_set_page(P3(gx_device_svga *, int, int));
gx_device_svga gs_tvga_device =
	svga_device(tvga_procs, "tvga", atiw_get_mode, atiw_set_mode, tvga_set_page);

/* Initialize the graphics mode. */
private int
tvga_open(gx_device *dev)
{       fb_dev->wnum_read = 1;
	fb_dev->wnum_write = 0;
	/* Select the proper video mode */
	   {    static const mode_info mode_table[] = {
		   {     640,  400, 0x5c        },
		   {     640,  480, 0x5d        },
		   {     800,  600, 0x5e        },
		   {     1024, 768, 0x62        },
		   {    -1, -1, -1      }
		};
		int code = svga_find_mode(dev, mode_table);
		if ( code < 0 ) return code;      /* mode not available */
		return svga_open(dev);
	   }
}

/* Set the current display page. */
private void
tvga_set_page(gx_device_svga *dev, int pn, int wnum)
{
	/* new mode */
	outportb(0x3c4, 0x0b);
	inportb(0x3c4);

	outportb(0x3c4, 0x0e);
	outportb(0x3c5, pn ^ 2);
}

/* ------ The Tseng Labs ET3000/4000 device ------ */

private dev_proc_open_device(tseng_open);
private gx_device_procs tseng_procs = svga_procs(tseng_open);
/* We can use the tseng_get/set_mode procedures. */
private void tseng_set_page(P3(gx_device_svga *, int, int));
gx_device_svga gs_tseng_device =
	svga_device(tseng_procs, "tseng", atiw_get_mode, atiw_set_mode, tseng_set_page);

/* Initialize the graphics mode. */
private int
tseng_open(gx_device *dev)
{	fb_dev->wnum_read = 1;
	fb_dev->wnum_write = 0;
	/* Select the proper video mode */
	   {	static const mode_info mode_table[] = {
		   {	 640,  350, 0x2d	},
		   {	 640,  480, 0x2e	},
		   {	 800,  600, 0x30	},
		   {	 1024, 768, 0x38	},
		   {	-1, -1, -1	}
		};
		int code = svga_find_mode(dev, mode_table);
		volatile_fb_ptr p0 = (volatile_fb_ptr)MK_PTR(regen, 0);
		if ( code < 0 ) return code;	/* mode not available */
		code = svga_open(dev);
		if ( code < 0 ) return 0;
		/* Figure out whether we have an ET3000 or an ET4000 */
		/* by playing with the segment register. */
		outportb(0x3cd, 0x44);
		*p0 = 4;		/* byte 0, page 4 */
		outportb(0x3cd, 0x40);
		*p0 = 3;		/* byte 0, page 0 */
		fb_dev->info.tseng.et_model = *p0;
					/* read page 0 if ET3000, */
					/* page 4 if ET4000 */
		return 0;
	   }
}

/* Set the current display page. */
private void
tseng_set_page(gx_device_svga *dev, int pn, int wnum)
{	/* The ET3000 has read page = 5:3, write page = 2:0; */
	/* the ET4000 has read page = 7:4, write page = 3:0. */
	int shift = dev->info.tseng.et_model;
	int mask = (1 << shift) - 1;
	if ( wnum ) pn <<= shift, mask <<= shift;
	outportb(0x3cd, (inportb(0x3cd) & ~mask) + pn);
}
