source: trunk/packages/xen-3.1/xen-3.1/linux-2.6-xen-sparse/arch/x86_64/kernel/early_printk-xen.c @ 34

#include <linux/console.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/screen_info.h>
#include <asm/io.h>
#include <asm/processor.h>
#include <asm/fcntl.h>

/* Simple VGA output */

#ifdef __i386__
#include <asm/setup.h>
#define VGABASE         (__ISA_IO_base + 0xb8000)
#else
#include <asm/bootsetup.h>
#define VGABASE         ((void __iomem *)0xffffffff800b8000UL)
#endif

#ifndef CONFIG_XEN
static int max_ypos = 25, max_xpos = 80;
static int current_ypos = 25, current_xpos = 0; 

static void early_vga_write(struct console *con, const char *str, unsigned n)
{
        char c;
        int  i, k, j;

        while ((c = *str++) != '\0' && n-- > 0) {
                if (current_ypos >= max_ypos) {
                        /* scroll 1 line up */
                        for (k = 1, j = 0; k < max_ypos; k++, j++) {
                                for (i = 0; i < max_xpos; i++) {
                                        writew(readw(VGABASE+2*(max_xpos*k+i)),
                                               VGABASE + 2*(max_xpos*j + i));
                                }
                        }
                        for (i = 0; i < max_xpos; i++)
                                writew(0x720, VGABASE + 2*(max_xpos*j + i));
                        current_ypos = max_ypos-1;
                }
                if (c == '\n') {
                        current_xpos = 0;
                        current_ypos++;
                } else if (c != '\r')  {
                        writew(((0x7 << 8) | (unsigned short) c),
                               VGABASE + 2*(max_xpos*current_ypos +
                                                current_xpos++));
                        if (current_xpos >= max_xpos) {
                                current_xpos = 0;
                                current_ypos++;
                        }
                }
        }
}

static struct console early_vga_console = {
        .name =         "earlyvga",
        .write =        early_vga_write,
        .flags =        CON_PRINTBUFFER,
        .index =        -1,
};

/* Serial functions loosely based on a similar package from Klaus P. Gerlicher */

static int early_serial_base = 0x3f8;  /* ttyS0 */

#define XMTRDY          0x20

#define DLAB            0x80

#define TXR             0       /*  Transmit register (WRITE) */
#define RXR             0       /*  Receive register  (READ)  */
#define IER             1       /*  Interrupt Enable          */
#define IIR             2       /*  Interrupt ID              */
#define FCR             2       /*  FIFO control              */
#define LCR             3       /*  Line control              */
#define MCR             4       /*  Modem control             */
#define LSR             5       /*  Line Status               */
#define MSR             6       /*  Modem Status              */
#define DLL             0       /*  Divisor Latch Low         */
#define DLH             1       /*  Divisor latch High        */

static int early_serial_putc(unsigned char ch)
{
        unsigned timeout = 0xffff;
        while ((inb(early_serial_base + LSR) & XMTRDY) == 0 && --timeout)
                cpu_relax();
        outb(ch, early_serial_base + TXR);
        return timeout ? 0 : -1;
}

static void early_serial_write(struct console *con, const char *s, unsigned n)
{
        while (*s && n-- > 0) {
                early_serial_putc(*s);
                if (*s == '\n')
                        early_serial_putc('\r');
                s++;
        }
}

#define DEFAULT_BAUD 9600

static __init void early_serial_init(char *s)
{
        unsigned char c;
        unsigned divisor;
        unsigned baud = DEFAULT_BAUD;
        char *e;

        if (*s == ',')
                ++s;

        if (*s) {
                unsigned port;
                if (!strncmp(s,"0x",2)) {
                        early_serial_base = simple_strtoul(s, &e, 16);
                } else {
                        static int bases[] = { 0x3f8, 0x2f8 };

                        if (!strncmp(s,"ttyS",4))
                                s += 4;
                        port = simple_strtoul(s, &e, 10);
                        if (port > 1 || s == e)
                                port = 0;
                        early_serial_base = bases[port];
                }
                s += strcspn(s, ",");
                if (*s == ',')
                        s++;
        }

        outb(0x3, early_serial_base + LCR);     /* 8n1 */
        outb(0, early_serial_base + IER);       /* no interrupt */
        outb(0, early_serial_base + FCR);       /* no fifo */
        outb(0x3, early_serial_base + MCR);     /* DTR + RTS */

        if (*s) {
                baud = simple_strtoul(s, &e, 0);
                if (baud == 0 || s == e)
                        baud = DEFAULT_BAUD;
        }

        divisor = 115200 / baud;
        c = inb(early_serial_base + LCR);
        outb(c | DLAB, early_serial_base + LCR);
        outb(divisor & 0xff, early_serial_base + DLL);
        outb((divisor >> 8) & 0xff, early_serial_base + DLH);
        outb(c & ~DLAB, early_serial_base + LCR);
}

#else /* CONFIG_XEN */

static void
early_serial_write(struct console *con, const char *s, unsigned count)
{
        int n;

        while (count > 0) {
                n = HYPERVISOR_console_io(CONSOLEIO_write, count, (char *)s);
                if (n <= 0)
                        break;
                count -= n;
                s += n;
        }
} 

static __init void early_serial_init(char *s)
{
}

/*
 * No early VGA console on Xen, as we do not have convenient ISA-space
 * mappings. Someone should fix this for domain 0. For now, use fake serial.
 */
#define early_vga_console early_serial_console

#endif

static struct console early_serial_console = {
        .name =         "earlyser",
        .write =        early_serial_write,
        .flags =        CON_PRINTBUFFER,
        .index =        -1,
};

/* Console interface to a host file on AMD's SimNow! */

static int simnow_fd;

enum {
        MAGIC1 = 0xBACCD00A,
        MAGIC2 = 0xCA110000,
        XOPEN = 5,
        XWRITE = 4,
};

static noinline long simnow(long cmd, long a, long b, long c)
{
        long ret;
        asm volatile("cpuid" :
                     "=a" (ret) :
                     "b" (a), "c" (b), "d" (c), "0" (MAGIC1), "D" (cmd + MAGIC2));
        return ret;
}

void __init simnow_init(char *str)
{
        char *fn = "klog";
        if (*str == '=')
                fn = ++str;
        /* error ignored */
        simnow_fd = simnow(XOPEN, (unsigned long)fn, O_WRONLY|O_APPEND|O_CREAT, 0644);
}

static void simnow_write(struct console *con, const char *s, unsigned n)
{
        simnow(XWRITE, simnow_fd, (unsigned long)s, n);
}

static struct console simnow_console = {
        .name =         "simnow",
        .write =        simnow_write,
        .flags =        CON_PRINTBUFFER,
        .index =        -1,
};

/* Direct interface for emergencies */
struct console *early_console = &early_vga_console;
static int early_console_initialized = 0;

void early_printk(const char *fmt, ...)
{
        char buf[512];
        int n;
        va_list ap;

        va_start(ap,fmt);
        n = vscnprintf(buf,512,fmt,ap);
        early_console->write(early_console,buf,n);
        va_end(ap);
}

static int __initdata keep_early;

int __init setup_early_printk(char *opt)
{
        char *space;
        char buf[256];

        if (early_console_initialized)
                return 1;

        strlcpy(buf,opt,sizeof(buf));
        space = strchr(buf, ' ');
        if (space)
                *space = 0;

        if (strstr(buf,"keep"))
                keep_early = 1;

        if (!strncmp(buf, "serial", 6)) {
                early_serial_init(buf + 6);
                early_console = &early_serial_console;
        } else if (!strncmp(buf, "ttyS", 4)) {
                early_serial_init(buf);
                early_console = &early_serial_console;
        } else if (!strncmp(buf, "vga", 3)
#ifndef CONFIG_XEN
                   && SCREEN_INFO.orig_video_isVGA == 1) {
                max_xpos = SCREEN_INFO.orig_video_cols;
                max_ypos = SCREEN_INFO.orig_video_lines;
                current_ypos = SCREEN_INFO.orig_y;
#else
                   || !strncmp(buf, "xen", 3)) {
#endif
                early_console = &early_vga_console;
        } else if (!strncmp(buf, "simnow", 6)) {
                simnow_init(buf + 6);
                early_console = &simnow_console;
                keep_early = 1;
        }
        early_console_initialized = 1;
        register_console(early_console);
        return 0;
}

void __init disable_early_printk(void)
{
        if (!early_console_initialized || !early_console)
                return;
        if (!keep_early) {
                printk("disabling early console\n");
                unregister_console(early_console);
                early_console_initialized = 0;
        } else {
                printk("keeping early console\n");
        }
}

__setup("earlyprintk=", setup_early_printk);