arch/x86/boot/early_serial_console.c

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