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#include <u.h>
#include <libc.h>
#include <bio.h>
#include </386/include/ureg.h>
typedef struct Ureg Ureg;

#include "pci.h"
#include "vga.h"

typedef struct Vbe Vbe;
typedef struct Vmode Vmode;
typedef struct Modelist Modelist;
typedef struct Edid Edid;

enum
{
        MemSize = 1024*1024,
        PageSize = 4096,
        RealModeBuf = 0x9000,
};

struct Vbe
{
        int     rmfd;   /* /dev/realmode */
        int     memfd;  /* /dev/realmem */
        uchar   *mem;   /* copy of memory; 1MB */
        uchar   *isvalid;       /* 1byte per 4kB in mem */
        uchar   *buf;
        uchar   *modebuf;
};

struct Vmode
{
        char    name[32];
        char    chan[32];
        int     id;
        int     attr;   /* flags */
        int     bpl;
        int     dx, dy;
        int     depth;
        char    *model;
        int     r, g, b, x;
        int     ro, go, bo, xo;
        int     directcolor;    /* flags */
        ulong   paddr;
};

struct Edid {
        char            mfr[4];         /* manufacturer */
        char            serialstr[16];  /* serial number as string (in extended data) */
        char            name[16];               /* monitor name as string (in extended data) */
        ushort  product;                /* product code, 0 = unused */
        ulong   serial;         /* serial number, 0 = unused */
        uchar   version;                /* major version number */
        uchar   revision;               /* minor version number */
        uchar   mfrweek;                /* week of manufacture, 0 = unused */
        int             mfryear;                /* year of manufacture, 0 = unused */
        uchar   dxcm;           /* horizontal image size in cm. */
        uchar   dycm;           /* vertical image size in cm. */
        int             gamma;          /* gamma*100 */
        int             rrmin;          /* minimum vertical refresh rate */
        int             rrmax;          /* maximum vertical refresh rate */
        int             hrmin;          /* minimum horizontal refresh rate */
        int             hrmax;          /* maximum horizontal refresh rate */
        ulong   pclkmax;                /* maximum pixel clock */
        int             flags;

        Modelist        *modelist;              /* list of supported modes */
};

struct Modelist
{
        Mode;
        Modelist *next;
};

enum {
        Fdigital = 1<<0,                /* is a digital display */
        Fdpmsstandby = 1<<1,    /* supports DPMS standby mode */
        Fdpmssuspend = 1<<2,    /* supports DPMS suspend mode */
        Fdpmsactiveoff = 1<<3,  /* supports DPMS active off mode */
        Fmonochrome = 1<<4,     /* is a monochrome display */
        Fgtf = 1<<5,            /* supports VESA GTF: see /public/doc/vesa/gtf10.pdf */
};

#define WORD(p) ((p)[0] | ((p)[1]<<8))
#define LONG(p) ((p)[0] | ((p)[1]<<8) | ((p)[2]<<16) | ((p)[3]<<24))
#define PWORD(p, v) (p)[0] = (v); (p)[1] = (v)>>8
#define PLONG(p, v) (p)[0] = (v); (p)[1] = (v)>>8; (p)[2] = (v)>>16; (p)[3] = (v)>>24

static Vbe *vbe;
static Edid edid;

Vbe *mkvbe(void);
int vbecheck(Vbe*);
uchar *vbemodes(Vbe*);
int vbemodeinfo(Vbe*, int, Vmode*);
int vbegetmode(Vbe*);
int vbesetmode(Vbe*, int);
void vbeprintinfo(Vbe*);
void vbeprintmodeinfo(Vbe*, int, char*);
int vbesnarf(Vbe*, Vga*);
void vesaddc(void);
int vbeddcedid(Vbe *vbe, Edid *e);
void printedid(Edid*);

int
dbvesa(Vga* vga)
{
        vbe = mkvbe();
        if(vbe == nil){
                fprint(2, "mkvbe: %r\n");
                return 0;
        }
        if(vbecheck(vbe) < 0){
                fprint(2, "dbvesa: %r\n");
                return 0;
        }
        vga->link = alloc(sizeof(Ctlr));
        *vga->link = vesa;
        vga->vesa = vga->link;
        vga->ctlr = vga->link;

        vga->link->link = alloc(sizeof(Ctlr));
        *vga->link->link = softhwgc;
        vga->hwgc = vga->link->link;

        return 1;
}

Mode*
dbvesamode(char *mode)
{
        int i;
        uchar *p, *ep;
        Vmode vm;
        Mode *m;
        
        if(vbe == nil)
                return nil;

        p = vbemodes(vbe);
        if(p == nil)
                return nil;
        for(ep=p+1024; (p[0]!=0xFF || p[1]!=0xFF) && p<ep; p+=2){
                if(vbemodeinfo(vbe, WORD(p), &vm) < 0)
                        continue;
                if(strcmp(vm.name, mode) == 0)
                        goto havemode;
        }
        if(1){
                fprint(2, "warning: scanning for unoffered vesa modes\n");
                for(i=0x100; i<0x200; i++){
                        if(vbemodeinfo(vbe, i, &vm) < 0)
                                continue;
                        if(strcmp(vm.name, mode) == 0)
                                goto havemode;
                }
        }
        werrstr("no such vesa mode");
        return nil;

havemode:
        m = alloc(sizeof(Mode));
        strcpy(m->type, "vesa");
        strcpy(m->size, vm.name);
        strcpy(m->chan, vm.chan);
        m->frequency = 100;
        m->x = vm.dx;
        m->y = vm.dy;
        m->z = vm.depth;
        m->ht = m->x;
        m->shb = m->x;
        m->ehb = m->x;
        m->shs = m->x;
        m->ehs = m->x;
        m->vt = m->y;
        m->vrs = m->y;
        m->vre = m->y;

        m->attr = alloc(sizeof(Attr));
        m->attr->attr = "id";
        m->attr->val = alloc(32);
        sprint(m->attr->val, "0x%x", vm.id);
        return m;
}

static void
snarf(Vga* vga, Ctlr* ctlr)
{
        if(!vbe)
                vbe = mkvbe();
        if(vbe)
                vga->vesa = ctlr;
        vbesnarf(vbe, vga);
        vga->linear = 1;
        ctlr->flag |= Hlinear|Ulinear;
}

static void
load(Vga* vga, Ctlr* ctlr)
{
        if(vbe == nil)
                error("no vesa bios\n");
        if(vbesetmode(vbe, atoi(dbattr(vga->mode->attr, "id"))) < 0){
                ctlr->flag |= Ferror;
                fprint(2, "vbesetmode: %r\n");
        }
}

static void
dump(Vga*, Ctlr*)
{
        int i;
        char did[0x200];
        uchar *p, *ep;

        if(!vbe){
                Bprint(&stdout, "no vesa bios\n");
                return;
        }

        memset(did, 0, sizeof did);
        vbeprintinfo(vbe);
        p = vbemodes(vbe);
        if(p){
                for(ep=p+1024; (p[0]!=0xFF || p[1]!=0xFF) && p<ep; p+=2){
                        vbeprintmodeinfo(vbe, WORD(p), "");
                        if(WORD(p) < nelem(did))
                                did[WORD(p)] = 1;
                }
        }
        for(i=0x100; i<0x1FF; i++)
                if(!did[i])
                        vbeprintmodeinfo(vbe, i, " (unoffered)");
                                
        
        if(vbeddcedid(vbe, &edid) < 0)
                fprint(2, "warning: reading edid: %r\n");
        else
                printedid(&edid);
}

Ctlr vesa = {
        "vesa",                 /* name */
        snarf,                          /* snarf */
        0,                      /* options */
        0,                              /* init */
        load,                           /* load */
        dump,                           /* dump */
};

Ctlr softhwgc = {
        "soft",
};

/*
 * VESA bios extension
 */

typedef struct Flag Flag;
struct Flag {
        int bit;
        char *desc;
};

static Flag capabilityflag[] = {
        0x01, "8-bit-dac",
        0x02, "not-vga",
        0x04, "ramdac-needs-blank",
        0x08, "stereoscopic",
        0x10, "stereo-evc",
        0
};

static Flag modeattributesflags[] = {
        1<<0, "supported",
        1<<2, "tty",
        1<<3, "color",
        1<<4, "graphics",
        1<<5, "not-vga",
        1<<6, "no-windowed-vga",
        1<<7, "linear",
        1<<8, "double-scan",
        1<<9, "interlace",
        1<<10, "triple-buffer",
        1<<11, "stereoscopic",
        1<<12, "dual-start-addr",
        0
};

static Flag winattributesflags[] = {
        1<<0, "relocatable",
        1<<1, "readable",
        1<<2, "writeable",
        0
};

static Flag directcolorflags[] = {
        1<<0, "programmable-color-ramp",
        1<<1, "x-usable",
        0
};

static char *modelstr[] = {
        "text", "cga", "hercules", "planar", "packed", "non-chain4", "direct", "YUV"
};

static void
printflags(Flag *f, int b)
{
        int i;

        for(i=0; f[i].bit; i++)
                if(f[i].bit & b)
                        Bprint(&stdout, " %s", f[i].desc);
        Bprint(&stdout, "\n");
}

Vbe*
mkvbe(void)
{
        Vbe *vbe;

        vbe = alloc(sizeof(Vbe));
        if((vbe->rmfd = open("/dev/realmode", ORDWR)) < 0)
                return nil;
        if((vbe->memfd = open("/dev/realmodemem", ORDWR)) < 0)
                return nil;
        vbe->mem = alloc(MemSize);
        vbe->isvalid = alloc(MemSize/PageSize);
        vbe->buf = alloc(PageSize);
        vbe->modebuf = alloc(PageSize);
        return vbe;
}

static void
loadpage(Vbe *vbe, int p)
{
        if(p >= MemSize/PageSize || vbe->isvalid[p])
                return;
        if(pread(vbe->memfd, vbe->mem+p*PageSize, PageSize, p*PageSize) != PageSize)
                error("read /dev/realmodemem: %r\n");
        vbe->isvalid[p] = 1;
}

static void*
unfarptr(Vbe *vbe, uchar *p)
{
        int seg, off;

        seg = WORD(p+2);
        off = WORD(p);
        if(seg==0 && off==0)
                return nil;
        off += seg<<4;
        if(off >= MemSize)
                return nil;
        loadpage(vbe, off/PageSize);
        loadpage(vbe, off/PageSize+1);  /* just in case */
        return vbe->mem+off;
}

uchar*
vbesetup(Vbe *vbe, Ureg *u, int ax)
{
        memset(vbe->buf, 0, PageSize);
        memset(u, 0, sizeof *u);
        u->ax = ax;
        u->es = (RealModeBuf>>4)&0xF000;
        u->di = RealModeBuf&0xFFFF;
        return vbe->buf;
}

int
vbecall(Vbe *vbe, Ureg *u)
{
        u->trap = 0x10;
        if(pwrite(vbe->memfd, vbe->buf, PageSize, RealModeBuf) != PageSize)
                error("write /dev/realmodemem: %r\n");
        if(pwrite(vbe->rmfd, u, sizeof *u, 0) != sizeof *u)
                error("write /dev/realmode: %r\n");
        if(pread(vbe->rmfd, u, sizeof *u, 0) != sizeof *u)
                error("read /dev/realmode: %r\n");
        if(pread(vbe->memfd, vbe->buf, PageSize, RealModeBuf) != PageSize)
                error("read /dev/realmodemem: %r\n");
        if((u->ax&0xFFFF) != 0x004F){
                werrstr("VBE error %#.4lux", u->ax&0xFFFF);
                return -1;
        }
        memset(vbe->isvalid, 0, MemSize/PageSize);
        return 0;
}

int
vbecheck(Vbe *vbe)
{
        uchar *p;
        Ureg u;

        p = vbesetup(vbe, &u, 0x4F00);
        strcpy((char*)p, "VBE2");
        if(vbecall(vbe, &u) < 0)
                return -1;
        if(memcmp(p, "VESA", 4) != 0 || p[5] < 2){
                werrstr("invalid vesa signature %.4H %.4H\n", p, p+4);
                return -1;
        }
        return 0;
}

int
vbesnarf(Vbe *vbe, Vga *vga)
{
        uchar *p;
        Ureg u;

        p = vbesetup(vbe, &u, 0x4F00);
        strcpy((char*)p, "VBE2");
        if(vbecall(vbe, &u) < 0)
                return -1;
        if(memcmp(p, "VESA", 4) != 0 || p[5] < 2)
                return -1;
        vga->apz = WORD(p+18)*0x10000UL;
        return 0;
}

void
vbeprintinfo(Vbe *vbe)
{
        uchar *p;
        Ureg u;

        p = vbesetup(vbe, &u, 0x4F00);
        strcpy((char*)p, "VBE2");
        if(vbecall(vbe, &u) < 0)
                return;

        printitem("vesa", "sig");
        Bprint(&stdout, "%.4s %d.%d\n", (char*)p, p[5], p[4]);
        if(p[5] < 2)
                return;

        printitem("vesa", "oem");
        Bprint(&stdout, "%s %d.%d\n", unfarptr(vbe, p+6), p[21], p[20]);
        printitem("vesa", "vendor");
        Bprint(&stdout, "%s\n", unfarptr(vbe, p+22));
        printitem("vesa", "product");
        Bprint(&stdout, "%s\n", unfarptr(vbe, p+26));
        printitem("vesa", "rev");
        Bprint(&stdout, "%s\n", unfarptr(vbe, p+30));

        printitem("vesa", "cap");
        printflags(capabilityflag, p[10]);

        printitem("vesa", "mem");
        Bprint(&stdout, "%lud\n", WORD(p+18)*0x10000UL);
}

uchar*
vbemodes(Vbe *vbe)
{
        uchar *p;
        Ureg u;

        p = vbesetup(vbe, &u, 0x4F00);
        strcpy((char*)p, "VBE2");
        if(vbecall(vbe, &u) < 0)
                return nil;
        memmove(vbe->modebuf, unfarptr(vbe, p+14), 1024);
        return vbe->modebuf;
}

int
vbemodeinfo(Vbe *vbe, int id, Vmode *m)
{
        int o;
        ulong d, c, x;
        uchar *p;
        char tmp[sizeof m->chan];
        Ureg u;

        p = vbesetup(vbe, &u, 0x4F01);
        u.cx = id;
        if(vbecall(vbe, &u) < 0)
                return -1;

        m->id = id;
        m->attr = WORD(p);
        m->bpl = WORD(p+16);
        m->dx = WORD(p+18);
        m->dy = WORD(p+20);
        m->depth = p[25];
        m->model = p[27] < nelem(modelstr) ? modelstr[p[27]] : "unknown";
        m->r = p[31];
        m->g = p[33];
        m->b = p[35];
        m->x = p[37];
        m->ro = p[32];
        m->go = p[34];
        m->bo = p[36];
        m->xo = p[38];
        m->directcolor = p[39];
        m->paddr = LONG(p+40);
        snprint(m->name, sizeof m->name, "%dx%dx%d",
                m->dx, m->dy, m->depth);
        if(m->depth <= 8) {
                snprint(m->chan, sizeof m->chan, "m%d", m->depth);
                return 0;
        }

        m->xo = m->x = 0;
        d = 1 << (m->depth - 1);
        d |= d - 1;
        c  = ((1<<m->r)-1) << m->ro;
        c |= ((1<<m->g)-1) << m->go;
        c |= ((1<<m->b)-1) << m->bo;
        x = d ^ c;
        if(x != 0){
                for(; (x & 1) == 0; x >>= 1)
                        m->xo++;
                for(; x & 1; x >>= 1)
                        m->x++;
        }

        m->chan[0] = o = 0;
        while(o < m->depth){
                if(m->r && m->ro == o){
                        snprint(tmp, sizeof tmp, "r%d%s", m->r, m->chan);
                        o += m->r;
                }else if(m->g && m->go == o){
                        snprint(tmp, sizeof tmp, "g%d%s", m->g, m->chan);
                        o += m->g;
                }else if(m->b && m->bo == o){
                        snprint(tmp, sizeof tmp, "b%d%s", m->b, m->chan);
                        o += m->b;
                }else if(m->x && m->xo == o){
                        snprint(tmp, sizeof tmp, "x%d%s", m->x, m->chan);
                        o += m->x;
                }else
                        break;
                strncpy(m->chan, tmp, sizeof m->chan);
        }
        return 0;
}

void
vbeprintmodeinfo(Vbe *vbe, int id, char *suffix)
{
        Vmode m;

        if(vbemodeinfo(vbe, id, &m) < 0){
        //      Bprint(&stdout, "vesa: cannot get mode 0x%ux: %r\n", id);
                return;
        }
        printitem("vesa", "mode");
        Bprint(&stdout, "0x%ux %s %s %s%s\n",
                m.id, m.name, m.chan, m.model, suffix);
}

int
vbegetmode(Vbe *vbe)
{
        Ureg u;

        vbesetup(vbe, &u, 0x4F03);
        if(vbecall(vbe, &u) < 0)
                return 0;
        return u.bx;
}

int
vbesetmode(Vbe *vbe, int id)
{
        uchar *p;
        Ureg u;

        p = vbesetup(vbe, &u, 0x4F02);
        if(id != 3)
                id |= 3<<14;    /* graphics: use linear, do not clear */
        u.bx = id;
        USED(p);
        /*
         * can set mode specifics (ht hss hse vt vss vse 0 clockhz refreshhz):
         *
                u.bx |= 1<<11;
                n = atoi(argv[2]); PWORD(p, n); p+=2;
                n = atoi(argv[3]); PWORD(p, n); p+=2;
                n = atoi(argv[4]); PWORD(p, n); p+=2;
                n = atoi(argv[5]); PWORD(p, n); p+=2;
                n = atoi(argv[6]); PWORD(p, n); p+=2;
                n = atoi(argv[7]); PWORD(p, n); p+=2;
                *p++ = atoi(argv[8]);
                n = atoi(argv[9]); PLONG(p, n); p += 4;
                n = atoi(argv[10]); PWORD(p, n); p += 2;
                if(p != vbe.buf+19){
                        fprint(2, "prog error\n");
                        return;
                }
         *
         */
        return vbecall(vbe, &u);
}

void
vesatextmode(void)
{
        if(vbe == nil){
                vbe = mkvbe();
                if(!vbe)
                        error("mkvbe: %r\n");
        }
        if(vbecheck(vbe) < 0)
                error("vbecheck: %r\n");
        if(vbesetmode(vbe, 3) < 0)
                error("vbesetmode: %r\n");
}

static Flag edidflags[] = {
        Fdigital, "digital",
        Fdpmsstandby, "standby",
        Fdpmssuspend, "suspend",
        Fdpmsactiveoff, "activeoff",
        Fmonochrome, "monochrome",
        Fgtf, "gtf",
        0
};

int parseedid128(Edid *e, void *v);

int
vbeddcedid(Vbe *vbe, Edid *e)
{
        uchar *p;
        Ureg u;
        
        p = vbesetup(vbe, &u, 0x4F15);
        u.bx = 0x0001;
        if(vbecall(vbe, &u) < 0)
                return -1;
        if(parseedid128(e, p) < 0){
                werrstr("parseedid128: %r");
                return -1;
        }
        return 0;
}
        
void
printedid(Edid *e)
{
        Modelist *l;
        
        printitem("edid", "mfr");
        Bprint(&stdout, "%s\n", e->mfr);
        printitem("edid", "serialstr");
        Bprint(&stdout, "%s\n", e->serialstr);
        printitem("edid", "name");
        Bprint(&stdout, "%s\n", e->name);
        printitem("edid", "product");
        Bprint(&stdout, "%d\n", e->product);
        printitem("edid", "serial");
        Bprint(&stdout, "%lud\n", e->serial);
        printitem("edid", "version");
        Bprint(&stdout, "%d.%d\n", e->version, e->revision);
        printitem("edid", "mfrdate");
        Bprint(&stdout, "%d.%d\n", e->mfryear, e->mfrweek);
        printitem("edid", "size (cm)");
        Bprint(&stdout, "%dx%d\n", e->dxcm, e->dycm);
        printitem("edid", "gamma");
        Bprint(&stdout, "%.2f\n", e->gamma/100.);
        printitem("edid", "vert (Hz)");
        Bprint(&stdout, "%d-%d\n", e->rrmin, e->rrmax);
        printitem("edid", "horz (Hz)");
        Bprint(&stdout, "%d-%d\n", e->hrmin, e->hrmax);
        printitem("edid", "pclkmax");
        Bprint(&stdout, "%lud\n", e->pclkmax);
        printitem("edid", "flags");
        printflags(edidflags, e->flags);
        
        for(l=e->modelist; l; l=l->next){
                printitem("edid", l->name);
                Bprint(&stdout, "\n\t\tclock=%g\n\t\tshb=%d ehb=%d ht=%d\n\t\tvrs=%d vre=%d vt=%d\n\t\thsync=%c vsync=%c %s\n",
                        l->frequency/1.e6, l->shb, l->ehb, l->ht, l->vrs, l->vre, l->vt, l->hsync?l->hsync:'?', l->vsync?l->vsync:'?', l->interlace?"interlace=v" : "");
        }
}

Modelist*
addmode(Modelist *l, Mode m)
{
        int rr;
        Modelist **lp;

//m.z = 8; // BUG
        rr = (m.frequency+m.ht*m.vt/2)/(m.ht*m.vt);
        snprint(m.name, sizeof m.name, "%dx%dx%d@%dHz", m.x, m.y, m.z, rr);

        if(m.shs == 0)
                m.shs = m.shb;
        if(m.ehs == 0)
                m.ehs = m.ehb;
        if(m.vbs == 0)
                m.vbs = m.vrs;
        if(m.vbe == 0)
                m.vbe = m.vbs+1;

        for(lp=&l; *lp; lp=&(*lp)->next){
                if(strcmp((*lp)->name, m.name) == 0){
                        (*lp)->Mode = m;
                        return l;
                }
        }

        *lp = alloc(sizeof(**lp));
        (*lp)->Mode = m;
        return l;
}

/*
 * Parse VESA EDID information.  Based on the VESA
 * Extended Display Identification Data standard, Version 3,
 * November 13, 1997.  See /public/doc/vesa/edidv3.pdf.
 *
 * This only handles 128-byte EDID blocks.  Until I find
 * a monitor that produces 256-byte blocks, I'm not going
 * to try to decode them.
 */

/*
 * Established timings block.  There is a bitmap
 * that says whether each mode is supported.  Most
 * of these have VESA definitions.  Those that don't are marked
 * as such, and we ignore them (the lookup fails).
 */
static char *estabtime[] = {
        "720x400@70Hz", /* non-VESA: IBM, VGA */
        "720x400@88Hz", /* non-VESA: IBM, XGA2 */
        "640x480@60Hz",
        "640x480@67Hz", /* non-VESA: Apple, Mac II */
        "640x480@72Hz",
        "640x480@75Hz",
        "800x600@56Hz",
        "800x600@60Hz",

        "800x600@72Hz",
        "800x600@75Hz",
        "832x624@75Hz", /* non-VESA: Apple, Mac II */
        "1024x768i@87Hz",       /* non-VESA: IBM */
        "1024x768@60Hz",
        "1024x768@70Hz",
        "1024x768@75Hz",
        "1280x1024@75Hz",

        "1152x870@75Hz",        /* non-VESA: Apple, Mac II */
};

/*
 * Decode the EDID detailed timing block.  See pp. 20-21 of the standard.
 */
static int
decodedtb(Mode *m, uchar *p)
{
        int ha, hb, hso, hspw, rr, va, vb, vso, vspw;
        /* int dxmm, dymm, hbord, vbord; */

        memset(m, 0, sizeof *m);

        m->frequency = ((p[1]<<8) | p[0]) * 10000;

        ha = ((p[4] & 0xF0)<<4) | p[2];         /* horizontal active */
        hb = ((p[4] & 0x0F)<<8) | p[3];         /* horizontal blanking */
        va = ((p[7] & 0xF0)<<4) | p[5];         /* vertical active */
        vb = ((p[7] & 0x0F)<<8) | p[6];         /* vertical blanking */
        hso = ((p[11] & 0xC0)<<2) | p[8];       /* horizontal sync offset */
        hspw = ((p[11] & 0x30)<<4) | p[9];      /* horizontal sync pulse width */
        vso = ((p[11] & 0x0C)<<2) | ((p[10] & 0xF0)>>4);        /* vertical sync offset */
        vspw = ((p[11] & 0x03)<<4) | (p[10] & 0x0F);            /* vertical sync pulse width */

        /* dxmm = (p[14] & 0xF0)<<4) | p[12];   /* horizontal image size (mm) */
        /* dymm = (p[14] & 0x0F)<<8) | p[13];   /* vertical image size (mm) */
        /* hbord = p[15];               /* horizontal border (pixels) */
        /* vbord = p[16];               /* vertical border (pixels) */

        m->x = ha;
        m->y = va;

        m->ht = ha+hb;
        m->shs = ha;
        m->shb = ha+hso;
        m->ehb = ha+hso+hspw;
        m->ehs = ha+hb;

        m->vt = va+vb;
        m->vbs = va;    
        m->vrs = va+vso;
        m->vre = va+vso+vspw;
        m->vbe = va+vb;

        if(p[17] & 0x80)        /* interlaced */
                m->interlace = 'v';

        if(p[17] & 0x60)        /* some form of stereo monitor mode; no support */
                return -1;

        /*
         * Sync signal description.  I have no idea how to properly handle the 
         * first three cases, which I think are aimed at things other than
         * canonical SVGA monitors.
         */
        switch((p[17] & 0x18)>>3) {
        case 0:  /* analog composite sync signal*/
        case 1: /* bipolar analog composite sync signal */
                /* p[17] & 0x04 means serration: hsync during vsync */
                /* p[17] & 0x02 means sync pulse appears on RGB not just G */
                break;

        case 2: /* digital composite sync signal */
                /* p[17] & 0x04 means serration: hsync during vsync */
                /* p[17] & 0x02 means hsync positive outside vsync */
                break;

        case 3: /* digital separate sync signal; the norm */
                m->vsync = (p[17] & 0x04) ? '+' : '-';
                m->hsync = (p[17] & 0x02) ? '+' : '-';
                break;
        }
        /* p[17] & 0x01 is another stereo bit, only referenced if p[17] & 0x60 != 0 */

        rr = (m->frequency+m->ht*m->vt/2) / (m->ht*m->vt);

        snprint(m->name, sizeof m->name, "%dx%d@%dHz", m->x, m->y, rr);

        return 0;
}

extern Mode *vesamodes[];

int
vesalookup(Mode *m, char *name)
{
        Mode **p;

        for(p=vesamodes; *p; p++)
                if(strcmp((*p)->name, name) == 0) {
                        *m = **p;
                        return 0;
                }

        return -1;
}

static int
decodesti(Mode *m, uchar *p)
{
        int x, y, rr;
        char str[20];

        x = (p[0]+31)*8;
        switch((p[1]>>6) & 3){
        default:
        case 0:
                y = x;
                break;
        case 1:
                y = (x*4)/3;
                break;
        case 2:
                y = (x*5)/4;
                break;
        case 3:
                y = (x*16)/9;
                break;
        }
        rr = (p[1] & 0x1F) + 60;

        sprint(str, "%dx%d@%dHz", x, y, rr);
        return vesalookup(m, str);
}

int
parseedid128(Edid *e, void *v)
{
        static uchar magic[8] = { 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00 };
        uchar *p, *q, sum;
        int dpms, estab, i, m, vid;
        Mode mode;

        memset(e, 0, sizeof *e);

        p = (uchar*)v;
        if(memcmp(p, magic, 8) != 0) {
                werrstr("bad edid header");
                return -1;
        }

        sum = 0;
        for(i=0; i<128; i++) 
                sum += p[i];
        if(sum != 0) {
                werrstr("bad edid checksum");
                return -1;
        }
        p += 8;

        assert(p == (uchar*)v+8);       /* assertion offsets from pp. 12-13 of the standard */
        /*
         * Manufacturer name is three 5-bit ascii letters, packed
         * into a big endian [sic] short in big endian order.  The high bit is unused.
         */
        i = (p[0]<<8) | p[1];
        p += 2;
        e->mfr[0] = 'A'-1 + ((i>>10) & 0x1F);
        e->mfr[1] = 'A'-1 + ((i>>5) & 0x1F);
        e->mfr[2] = 'A'-1 + (i & 0x1F);
        e->mfr[3] = '\0';

        /*
         * Product code is a little endian short.
         */
        e->product = (p[1]<<8) | p[0];
        p += 2;

        /*
         * Serial number is a little endian long, 0x01010101 = unused.
         */
        e->serial = (p[3]<<24) | (p[2]<<16) | (p[1]<<8) | p[0];
        p += 4;
        if(e->serial == 0x01010101)
                e->serial = 0;

        e->mfrweek = *p++;
        e->mfryear = 1990 + *p++;

        assert(p == (uchar*)v+8+10);
        /*
         * Structure version is next two bytes: major.minor.
         */
        e->version = *p++;
        e->revision = *p++;

        assert(p == (uchar*)v+8+10+2);
        /*
         * Basic display parameters / features.
         */
        /*
         * Video input definition byte: 0x80 tells whether it is
         * an analog or digital screen; we ignore the other bits.
         * See p. 15 of the standard.
         */
        vid = *p++;
        if(vid & 0x80)
                e->flags |= Fdigital;

        e->dxcm = *p++;
        e->dycm = *p++;
        e->gamma = 100 + *p++;
        dpms = *p++;
        if(dpms & 0x80)
                e->flags |= Fdpmsstandby;
        if(dpms & 0x40)
                e->flags |= Fdpmssuspend;
        if(dpms & 0x20)
                e->flags |= Fdpmsactiveoff;
        if((dpms & 0x18) == 0x00)
                e->flags |= Fmonochrome;
        if(dpms & 0x01)
                e->flags |= Fgtf;

        assert(p == (uchar*)v+8+10+2+5);
        /*
         * Color characteristics currently ignored.
         */
        p += 10;

        assert(p == (uchar*)v+8+10+2+5+10);
        /*
         * Established timings: a bitmask of 19 preset timings.
         */
        estab = (p[0]<<16) | (p[1]<<8) | p[2];
        p += 3;
        
        for(i=0, m=1<<23; i<nelem(estabtime); i++, m>>=1)
                if(estab & m)
                        if(vesalookup(&mode, estabtime[i]) == 0)
                                e->modelist = addmode(e->modelist,  mode);

        assert(p == (uchar*)v+8+10+2+5+10+3);
        /*
         * Standard Timing Identifications: eight 2-byte selectors
         * of more standard timings.
         */
        for(i=0; i<8; i++, p+=2)
                if(decodesti(&mode, p+2*i) == 0)
                        e->modelist = addmode(e->modelist, mode);

        assert(p == (uchar*)v+8+10+2+5+10+3+16);
        /*
         * Detailed Timings
         */
fprint(2, "dt\n");
        for(i=0; i<4; i++, p+=18) {
fprint(2, "%.8H\n", p);
                if(p[0] || p[1]) {      /* detailed timing block: p[0] or p[1] != 0 */
                        if(decodedtb(&mode, p) == 0)
                                e->modelist = addmode(e->modelist, mode);
                } else if(p[2]==0) {    /* monitor descriptor block */
                        switch(p[3]) {
                        case 0xFF:      /* monitor serial number (13-byte ascii, 0A terminated) */
                                if(q = memchr(p+5, 0x0A, 13))
                                        *q = '\0';
                                memset(e->serialstr, 0, sizeof(e->serialstr));
                                strncpy(e->serialstr, (char*)p+5, 13);
                                break;
                        case 0xFE:      /* ascii string (13-byte ascii, 0A terminated) */
                                break;
                        case 0xFD:      /* monitor range limits */
                                print("fd %.18H\n", p);
                                e->rrmin = p[5];
                                e->rrmax = p[6];
                                e->hrmin = p[7]*1000;
                                e->hrmax = p[8]*1000;
                                if(p[9] != 0xFF)
                                        e->pclkmax = p[9]*10*1000000;
                                break;
                        case 0xFC:      /* monitor name (13-byte ascii, 0A terminated) */
                                if(q = memchr(p+5, 0x0A, 13))
                                        *q = '\0';
                                memset(e->name, 0, sizeof(e->name));
                                strncpy(e->name, (char*)p+5, 13);
                                break;
                        case 0xFB:      /* extra color point data */
                                break;
                        case 0xFA:      /* extra standard timing identifications */
                                for(i=0; i<6; i++)
                                        if(decodesti(&mode, p+5+2*i) == 0)
                                                e->modelist = addmode(e->modelist, mode);
                                break;
                        }
                }
        }

        assert(p == (uchar*)v+8+10+2+5+10+3+16+72);
        return 0;
}