/**
 ** VESA.C ---- VESA compatible paging routines
 **
 ** Copyright (C) 1991 DJ Delorie, 24 Kirsten Ave, Rochester NH 03867-2954
 ** Copyright (C) 1992 Csaba Biegl, 820 Stirrup Dr, Nashville, TN 37221
 ** Copyright (C) 1993 Grzegorz Mazur, gbm@ii.pw.edu.pl
 **
 ** This file is distributed under the terms listed in the document
 ** "copying.dj", available from DJ Delorie at the address above.
 ** A copy of "copying.dj" should accompany this file; if not, a copy
 ** should be available from where this file was obtained.  This file
 ** may not be distributed without a verbatim copy of "copying.dj".
 **
 ** This file is distributed WITHOUT ANY WARRANTY; without even the implied
 ** warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 **/

int  VESA_win_write = 0;	/* VESA window index of the writable page */
int  VESA_win_read  = (-1);	/* VESA window index of the readable page */

void far paging_routine(void)
{
	return;
}

void far VESA_paging_routine(void)
{
	asm push    ds;
	asm push    es;
	asm mov	    cl,BYTE PTR cs:[driver_header.page_gran_shift];
	asm mov	    dl,al;
	asm xor	    dh,dh;
	asm shl	    dx,cl;				/* DX: write window (A or B) index */
	asm mov	    al,ah;
	asm xor	    ah,ah;
	asm shl	    ax,cl;				/* AX: read window index */
	asm mov	    bx,WORD PTR cs:[VESA_win_write];	/* index (A or B) of write window */
	asm cmp	    bx,(-1);				/* set it ? */
	asm je	    set_read_window;
	asm push    ax;					/* save read window */
	asm mov	    ax,0x4f05;
	asm call    DWORD PTR cs:[driver_header.VESA_paging_fnc];
	asm pop	    ax;
set_read_window:
	asm mov	    bx,WORD PTR cs:[VESA_win_read];	/* index (A or B) of read window */
	asm cmp	    bx,(-1);				/* set it ? */
	asm je	    paging_done;
	asm mov	    dx,ax;
	asm mov	    ax,0x4f05;
	asm call    DWORD PTR cs:[driver_header.VESA_paging_fnc];
paging_done:
	asm pop	    es;
	asm pop	    ds;
	asm mov	    al,8;				/* reconfig GR CTRL port for mask writes */
	asm mov	    dx,0x3ce;				/* GRX expects it in 16 color modes, and */
	asm out	    dx,al;				/* the paging func may have changed it */
	return;
}

int setup_VESA_paging(GrModeEntry *md)
{
	ModeInfoBlock *mb = VESAgetModeInfo(md->mode.vdr.BIOS_mode);
	int winsize,wingran,Aattr,Battr,Sdiff;

	if(!mb || !(mb->ModeAttributes & MODE_ISGRAPHICS)) {
	    VESA_win_read  = (-1);
	    VESA_win_write = (-1);
	    driver_header.VESA_paging_fnc = 0L;
	    driver_header.paging_routine  = FP_OFF(paging_routine);
	    return(GRD_NO_RW);
	}

	/* size and granularity must be pwr of 2! */
	for(winsize = 0; (1 << winsize) < mb->WinSize;	      winsize++) ;
	for(wingran = 0; (1 << wingran) < mb->WinGranularity; wingran++) ;
	if((1 << winsize) != mb->WinSize)	 return(-1);
	if((1 << wingran) != mb->WinGranularity) return(-1);

	/* check window attributes */
	Aattr = mb->WinAAttributes;
	Battr = mb->WinBAttributes;
	Sdiff = mb->WinBSegment - mb->WinASegment;
	Aattr &= (Aattr & WIN_SUPPORTED) ? (WIN_READABLE | WIN_WRITABLE) : 0;
	Battr &= (Battr & WIN_SUPPORTED) ? (WIN_READABLE | WIN_WRITABLE) : 0;

	/* cases with two adjacent split R/W pages (ATI) */
	if((Aattr == (WIN_READABLE | WIN_WRITABLE)) &&
	   (Battr == (WIN_READABLE | WIN_WRITABLE)) &&
	   (Sdiff == ((1024 / 16) << winsize))) {
	    driver_header.wr_page_start = mb->WinASegment;
	    driver_header.rd_page_start = mb->WinBSegment;
	    VESA_win_write = 0;
	    VESA_win_read  = 1;
	}
	else if((Aattr == (WIN_READABLE | WIN_WRITABLE)) &&
		(Battr == (WIN_READABLE | WIN_WRITABLE)) &&
		(Sdiff == ((-1024 / 16) << winsize))) {
	    driver_header.wr_page_start = mb->WinBSegment;
	    driver_header.rd_page_start = mb->WinASegment;
	    VESA_win_write = 1;
	    VESA_win_read  = 0;
	}

	/* cases with one full R and one full W page (Tseng 4000) */
	else if((Aattr & WIN_READABLE) &&
		(Battr & WIN_WRITABLE) &&
		(Sdiff == 0)) {
	    driver_header.wr_page_start = mb->WinBSegment;
	    driver_header.rd_page_start = mb->WinASegment;
	    VESA_win_write = 1;
	    VESA_win_read  = 0;
	}
	else if((Aattr & WIN_WRITABLE) &&
		(Battr & WIN_READABLE) &&
		(Sdiff == 0)) {
	    driver_header.wr_page_start = mb->WinASegment;
	    driver_header.rd_page_start = mb->WinBSegment;
	    VESA_win_write = 0;
	    VESA_win_read  = 1;
	}

	/* single page cases (Trident) */
	else if(Aattr == (WIN_WRITABLE | WIN_READABLE)) {
	    driver_header.wr_page_start = mb->WinASegment;
	    driver_header.rd_page_start = 0xffff;
	    VESA_win_write = 0;
	    VESA_win_read  = (-1);
	}
	else if(Battr == (WIN_WRITABLE | WIN_READABLE)) {
	    driver_header.wr_page_start = mb->WinBSegment;
	    driver_header.rd_page_start = 0xffff;
	    VESA_win_write = 1;
	    VESA_win_read  = (-1);
	}
	/* cannot use the paging scheme of this card */
	else return(-1);

	/* setup header variables */
	driver_header.page_size_shift = winsize - 2;	     /* in 4kByte units */
	driver_header.page_gran_shift = winsize - wingran;
	driver_header.line_offset     = mb->BytesPerScanLine;
	driver_header.VESA_paging_fnc = mb->WinFuncPtr;
	driver_header.paging_routine  = FP_OFF(VESA_paging_routine);
	return((VESA_win_read == (-1)) ? GRD_NO_RW : GRD_RW_64K);
}