LXR linux/arch/x86/boot/early_serial

   1#include "boot.h"
   2
   3#define DEFAULT_SERIAL_PORT 0x3f8 /* ttyS0 */
   4
   5#define XMTRDY          0x20
   6
   7#define DLAB            0x80
   8
   9#define TXR             0       /*  Transmit register (WRITE) */
  10#define RXR             0       /*  Receive register  (READ)  */
  11#define IER             1       /*  Interrupt Enable          */
  12#define IIR             2       /*  Interrupt ID              */
  13#define FCR             2       /*  FIFO control              */
  14#define LCR             3       /*  Line control              */
  15#define MCR             4       /*  Modem control             */
  16#define LSR             5       /*  Line Status               */
  17#define MSR             6       /*  Modem Status              */
  18#define DLL             0       /*  Divisor Latch Low         */
  19#define DLH             1       /*  Divisor latch High        */
  20
  21#define DEFAULT_BAUD 9600
  22
  23static void early_serial_init(int port, int baud)
  24{
  25        unsigned char c;
  26        unsigned divisor;
  27
  28        outb(0x3, port + LCR);  /* 8n1 */
  29        outb(0, port + IER);    /* no interrupt */
  30        outb(0, port + FCR);    /* no fifo */
  31        outb(0x3, port + MCR);  /* DTR + RTS */
  32
  33        divisor = 115200 / baud;
  34        c = inb(port + LCR);
  35        outb(c | DLAB, port + LCR);
  36        outb(divisor & 0xff, port + DLL);
  37        outb((divisor >> 8) & 0xff, port + DLH);
  38        outb(c & ~DLAB, port + LCR);
  39
  40        early_serial_base = port;
  41}
  42
  43static void parse_earlyprintk(void)
  44{
  45        int baud = DEFAULT_BAUD;
  46        char arg[32];
  47        int pos = 0;
  48        int port = 0;
  49
  50        if (cmdline_find_option("earlyprintk", arg, sizeof arg) > 0) {
  51                char *e;
  52
  53                if (!strncmp(arg, "serial", 6)) {
  54                        port = DEFAULT_SERIAL_PORT;
  55                        pos += 6;
  56                }
  57
  58                if (arg[pos] == ',')
  59                        pos++;
  60
  61                /*
  62                 * make sure we have
  63                 *      "serial,0x3f8,115200"
  64                 *      "serial,ttyS0,115200"
  65                 *      "ttyS0,115200"
  66                 */
  67                if (pos == 7 && !strncmp(arg + pos, "0x", 2)) {
  68                        port = simple_strtoull(arg + pos, &e, 16);
  69                        if (port == 0 || arg + pos == e)
  70                                port = DEFAULT_SERIAL_PORT;
  71                        else
  72                                pos = e - arg;
  73                } else if (!strncmp(arg + pos, "ttyS", 4)) {
  74                        static const int bases[] = { 0x3f8, 0x2f8 };
  75                        int idx = 0;
  76
  77                        if (!strncmp(arg + pos, "ttyS", 4))
  78                                pos += 4;
  79
  80                        if (arg[pos++] == '1')
  81                                idx = 1;
  82
  83                        port = bases[idx];
  84                }
  85
  86                if (arg[pos] == ',')
  87                        pos++;
  88
  89                baud = simple_strtoull(arg + pos, &e, 0);
  90                if (baud == 0 || arg + pos == e)
  91                        baud = DEFAULT_BAUD;
  92        }
  93
  94        if (port)
  95                early_serial_init(port, baud);
  96}
  97
  98#define BASE_BAUD (1843200/16)
  99static unsigned int probe_baud(int port)
 100{
 101        unsigned char lcr, dll, dlh;
 102        unsigned int quot;
 103
 104        lcr = inb(port + LCR);
 105        outb(lcr | DLAB, port + LCR);
 106        dll = inb(port + DLL);
 107        dlh = inb(port + DLH);
 108        outb(lcr, port + LCR);
 109        quot = (dlh << 8) | dll;
 110
 111        return BASE_BAUD / quot;
 112}
 113
 114static void parse_console_uart8250(void)
 115{
 116        char optstr[64], *options;
 117        int baud = DEFAULT_BAUD;
 118        int port = 0;
 119
 120        /*
 121         * console=uart8250,io,0x3f8,115200n8
 122         * need to make sure it is last one console !
 123         */
 124        if (cmdline_find_option("console", optstr, sizeof optstr) <= 0)
 125                return;
 126
 127        options = optstr;
 128
 129        if (!strncmp(options, "uart8250,io,", 12))
 130                port = simple_strtoull(options + 12, &options, 0);
 131        else if (!strncmp(options, "uart,io,", 8))
 132                port = simple_strtoull(options + 8, &options, 0);
 133        else
 134                return;
 135
 136        if (options && (options[0] == ','))
 137                baud = simple_strtoull(options + 1, &options, 0);
 138        else
 139                baud = probe_baud(port);
 140
 141        if (port)
 142                early_serial_init(port, baud);
 143}
 144
 145void console_init(void)
 146{
 147        parse_earlyprintk();
 148
 149        if (!early_serial_base)
 150                parse_console_uart8250();
 151}
 152