SchOS/cmd/fbinfo/main.c

// fbinfo -- ask /dev/fb0 what it is, and optionally draw on it.
//
// This exists because the framebuffer is the one device whose correctness you
// cannot check by reading kernel source: the numbers have to come back from
// the hardware the bootloader actually programmed. Three places in the kernel
// used to assume the framebuffer lived at 0xfd000000 and was 800x600x32; they
// agreed with QEMU's stdvga by luck, and nothing would have told us when the
// luck ran out. Now `fbinfo` would.
//
//   fbinfo        print the geometry
//   fbinfo fill   draw a gradient over the whole screen through mmap
//   fbinfo bars   draw colour bars through write(), no mmap involved
//
// The two drawing modes take different paths on purpose. If `fill` works and
// `bars` does not, the mapping is right and the device's read/write is wrong;
// if it is the other way round, the reverse. Having both makes a failure say
// which half broke.

#include "types.h"
#include "user.h"
#include "fcntl.h"
#include "fb.h"

#define PROT_READ  0x1
#define PROT_WRITE 0x2
#define MAP_SHARED 0x01

static void
puts(const char *s)
{
    int n = 0;
    while (s[n]) n++;
    write(1, (void*)s, n);
}

// Unsigned decimal. No printf in lib/, and pulling one in for six numbers
// would be a worse trade than fourteen lines.
static void
putu(unsigned long v)
{
    char buf[24];
    int i = 0;

    if (v == 0) {
        write(1, "0", 1);
        return;
    }
    while (v > 0 && i < (int)sizeof(buf)) {
        buf[i++] = (char)('0' + (v % 10));
        v /= 10;
    }
    while (i > 0) {
        i--;
        write(1, &buf[i], 1);
    }
}

static void
puthex(unsigned long v)
{
    static const char d[] = "0123456789abcdef";
    char buf[16];
    int i = 0;

    write(1, "0x", 2);
    if (v == 0) {
        write(1, "0", 1);
        return;
    }
    while (v > 0 && i < (int)sizeof(buf)) {
        buf[i++] = d[v & 0xf];
        v >>= 4;
    }
    while (i > 0) {
        i--;
        write(1, &buf[i], 1);
    }
}

// Name, then spaces out to a fixed column. Padding inside each string
// literal is what produced "bits_per_pixel32": the longest name happened to
// be exactly as wide as the column, so it got no separator at all and the
// value ran straight into it.
static void
label(const char *name)
{
    int n = 0;
    while (name[n]) n++;
    write(1, (void*)name, n);
    while (n < 16) { write(1, " ", 1); n++; }
}

static void
field(const char *name, unsigned long v)
{
    label(name);
    putu(v);
    puts("\n");
}

static void
chanline(const char *name, struct fb_bitfield *b)
{
    label(name);
    puts("offset ");
    putu(b->offset);
    puts(", length ");
    putu(b->length);
    if (b->length == 0)
        puts("  (absent)");
    puts("\n");
}

int
main(int argc, char *argv[])
{
    struct fb_var_screeninfo var;
    struct fb_fix_screeninfo fix;
    int fd;

    fd = open("/dev/fb0", O_RDWR);
    if (fd < 0) {
        puts("fbinfo: cannot open /dev/fb0\n");
        return 1;
    }

    if (ioctl(fd, FBIOGET_VSCREENINFO, &var) < 0) {
        puts("fbinfo: FBIOGET_VSCREENINFO failed\n");
        return 1;
    }
    if (ioctl(fd, FBIOGET_FSCREENINFO, &fix) < 0) {
        puts("fbinfo: FBIOGET_FSCREENINFO failed\n");
        return 1;
    }

    if (argc < 2) {
        label("id");
        puts(fix.id);
        puts("\n");
        field("xres", var.xres);
        field("yres", var.yres);
        field("bits_per_pixel", var.bits_per_pixel);
        label("smem_start");
        puthex(fix.smem_start);
        puts("\n");
        field("smem_len", fix.smem_len);
        field("line_length", fix.line_length);

        // The stride is the number worth staring at. A card is free to pad
        // each row, and a program that computes row starts as
        // y * xres * bytes_per_pixel instead of y * line_length draws a
        // picture that shears progressively down the screen.
        if (fix.line_length != var.xres * (var.bits_per_pixel / 8)) {
            label("note");
            puts("stride is padded; rows are not xres*bpp/8 apart\n");
        }

        chanline("red", &var.red);
        chanline("green", &var.green);
        chanline("blue", &var.blue);
        chanline("transp", &var.transp);
        return 0;
    }

    if (argv[1][0] == 'f') {           // fill
        unsigned char *fb = mmap(0, fix.smem_len,
                                 PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
        if (fb == 0 || (long)fb < 0) {
            puts("fbinfo: mmap failed\n");
            return 1;
        }
        unsigned bpp = var.bits_per_pixel / 8;
        for (unsigned y = 0; y < var.yres; y++) {
            unsigned char *row = fb + (unsigned long)y * fix.line_length;
            for (unsigned x = 0; x < var.xres; x++) {
                unsigned r = (x * 255) / (var.xres ? var.xres : 1);
                unsigned g = (y * 255) / (var.yres ? var.yres : 1);
                unsigned long px = ((unsigned long)r << var.red.offset) |
                                   ((unsigned long)g << var.green.offset) |
                                   ((unsigned long)0x80 << var.blue.offset);
                unsigned char *p = row + (unsigned long)x * bpp;
                for (unsigned b = 0; b < bpp; b++)
                    p[b] = (unsigned char)(px >> (b * 8));
            }
        }
        puts("fbinfo: gradient drawn through mmap\n");
        return 0;
    }

    if (argv[1][0] == 'b') {           // bars
        // One scanline at a time through write(). No mapping: this is the
        // path that used to be devsw's nullwrite, i.e. a silent no-op.
        static unsigned char row[8192];
        unsigned bpp = var.bits_per_pixel / 8;
        unsigned len = fix.line_length;
        if (len > sizeof(row))
            len = sizeof(row);

        for (unsigned y = 0; y < var.yres; y++) {
            unsigned band = (y * 8) / (var.yres ? var.yres : 1);
            unsigned long px =
                ((unsigned long)((band & 1) ? 255 : 0) << var.red.offset) |
                ((unsigned long)((band & 2) ? 255 : 0) << var.green.offset) |
                ((unsigned long)((band & 4) ? 255 : 0) << var.blue.offset);
            for (unsigned x = 0; x * bpp + bpp <= len; x++)
                for (unsigned b = 0; b < bpp; b++)
                    row[x * bpp + b] = (unsigned char)(px >> (b * 8));
            if (write(fd, row, len) != (int)len) {
                puts("fbinfo: short write to /dev/fb0\n");
                return 1;
            }
        }
        puts("fbinfo: colour bars drawn through write()\n");
        return 0;
    }

    puts("usage: fbinfo [fill|bars]\n");
    return 1;
}