early_serial_console.c

Go to the documentation of this file.

#include "boot.h"

#define DEFAULT_SERIAL_PORT 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        */

#define DEFAULT_BAUD 9600

static void early_serial_init(int port, int baud)
{
    unsigned char c;
    unsigned divisor;

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

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

    early_serial_base = port;
}

static void parse_earlyprintk(void)
{
    int baud = DEFAULT_BAUD;
    char arg[32];
    int pos = 0;
    int port = 0;

    if (cmdline_find_option("earlyprintk", arg, sizeof arg) > 0) {
        char *e;

        if (!strncmp(arg, "serial", 6)) {
            port = DEFAULT_SERIAL_PORT;
            pos += 6;
        }

        if (arg[pos] == ',')
            pos++;

        /*
         * make sure we have
         *  "serial,0x3f8,115200"
         *  "serial,ttyS0,115200"
         *  "ttyS0,115200"
         */
        if (pos == 7 && !strncmp(arg + pos, "0x", 2)) {
            port = simple_strtoull(arg + pos, &e, 16);
            if (port == 0 || arg + pos == e)
                port = DEFAULT_SERIAL_PORT;
            else
                pos = e - arg;
        } else if (!strncmp(arg + pos, "ttyS", 4)) {
            static const int bases[] = { 0x3f8, 0x2f8 };
            int idx = 0;

            if (!strncmp(arg + pos, "ttyS", 4))
                pos += 4;

            if (arg[pos++] == '1')
                idx = 1;

            port = bases[idx];
        }

        if (arg[pos] == ',')
            pos++;

        baud = simple_strtoull(arg + pos, &e, 0);
        if (baud == 0 || arg + pos == e)
            baud = DEFAULT_BAUD;
    }

    if (port)
        early_serial_init(port, baud);
}

#define BASE_BAUD (1843200/16)
static unsigned int probe_baud(int port)
{
    unsigned char lcr, dll, dlh;
    unsigned int quot;

    lcr = inb(port + LCR);
    outb(lcr | DLAB, port + LCR);
    dll = inb(port + DLL);
    dlh = inb(port + DLH);
    outb(lcr, port + LCR);
    quot = (dlh << 8) | dll;

    return BASE_BAUD / quot;
}

static void parse_console_uart8250(void)
{
    char optstr[64], *options;
    int baud = DEFAULT_BAUD;
    int port = 0;

    /*
     * console=uart8250,io,0x3f8,115200n8
     * need to make sure it is last one console !
     */
    if (cmdline_find_option("console", optstr, sizeof optstr) <= 0)
        return;

    options = optstr;

    if (!strncmp(options, "uart8250,io,", 12))
        port = simple_strtoull(options + 12, &options, 0);
    else if (!strncmp(options, "uart,io,", 8))
        port = simple_strtoull(options + 8, &options, 0);
    else
        return;

    if (options && (options[0] == ','))
        baud = simple_strtoull(options + 1, &options, 0);
    else
        baud = probe_baud(port);

    if (port)
        early_serial_init(port, baud);
}

void console_init(void)
{
    parse_earlyprintk();

    if (!early_serial_base)
        parse_console_uart8250();
}