root/arch/x86/boot/early_serial_console.c

DEFINITIONS

1. early_serial_init
2. parse_earlyprintk
3. probe_baud
4. parse_console_uart8250
5. console_init

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Serial port routines for use during early boot reporting. This code is
   4  * included from both the compressed kernel and the regular kernel.
   5  */
   6 #include "boot.h"
   7 
   8 #define DEFAULT_SERIAL_PORT 0x3f8 /* ttyS0 */
   9 
  10 #define DLAB            0x80
  11 
  12 #define TXR             0       /*  Transmit register (WRITE) */
  13 #define RXR             0       /*  Receive register  (READ)  */
  14 #define IER             1       /*  Interrupt Enable          */
  15 #define IIR             2       /*  Interrupt ID              */
  16 #define FCR             2       /*  FIFO control              */
  17 #define LCR             3       /*  Line control              */
  18 #define MCR             4       /*  Modem control             */
  19 #define LSR             5       /*  Line Status               */
  20 #define MSR             6       /*  Modem Status              */
  21 #define DLL             0       /*  Divisor Latch Low         */
  22 #define DLH             1       /*  Divisor latch High        */
  23 
  24 #define DEFAULT_BAUD 9600
  25 
  26 static void early_serial_init(int port, int baud)
  27 {
  28         unsigned char c;
  29         unsigned divisor;
  30 
  31         outb(0x3, port + LCR);  /* 8n1 */
  32         outb(0, port + IER);    /* no interrupt */
  33         outb(0, port + FCR);    /* no fifo */
  34         outb(0x3, port + MCR);  /* DTR + RTS */
  35 
  36         divisor = 115200 / baud;
  37         c = inb(port + LCR);
  38         outb(c | DLAB, port + LCR);
  39         outb(divisor & 0xff, port + DLL);
  40         outb((divisor >> 8) & 0xff, port + DLH);
  41         outb(c & ~DLAB, port + LCR);
  42 
  43         early_serial_base = port;
  44 }
  45 
  46 static void parse_earlyprintk(void)
  47 {
  48         int baud = DEFAULT_BAUD;
  49         char arg[32];
  50         int pos = 0;
  51         int port = 0;
  52 
  53         if (cmdline_find_option("earlyprintk", arg, sizeof(arg)) > 0) {
  54                 char *e;
  55 
  56                 if (!strncmp(arg, "serial", 6)) {
  57                         port = DEFAULT_SERIAL_PORT;
  58                         pos += 6;
  59                 }
  60 
  61                 if (arg[pos] == ',')
  62                         pos++;
  63 
  64                 /*
  65                  * make sure we have
  66                  *      "serial,0x3f8,115200"
  67                  *      "serial,ttyS0,115200"
  68                  *      "ttyS0,115200"
  69                  */
  70                 if (pos == 7 && !strncmp(arg + pos, "0x", 2)) {
  71                         port = simple_strtoull(arg + pos, &e, 16);
  72                         if (port == 0 || arg + pos == e)
  73                                 port = DEFAULT_SERIAL_PORT;
  74                         else
  75                                 pos = e - arg;
  76                 } else if (!strncmp(arg + pos, "ttyS", 4)) {
  77                         static const int bases[] = { 0x3f8, 0x2f8 };
  78                         int idx = 0;
  79 
  80                         /* += strlen("ttyS"); */
  81                         pos += 4;
  82 
  83                         if (arg[pos++] == '1')
  84                                 idx = 1;
  85 
  86                         port = bases[idx];
  87                 }
  88 
  89                 if (arg[pos] == ',')
  90                         pos++;
  91 
  92                 baud = simple_strtoull(arg + pos, &e, 0);
  93                 if (baud == 0 || arg + pos == e)
  94                         baud = DEFAULT_BAUD;
  95         }
  96 
  97         if (port)
  98                 early_serial_init(port, baud);
  99 }
 100 
 101 #define BASE_BAUD (1843200/16)
 102 static unsigned int probe_baud(int port)
 103 {
 104         unsigned char lcr, dll, dlh;
 105         unsigned int quot;
 106 
 107         lcr = inb(port + LCR);
 108         outb(lcr | DLAB, port + LCR);
 109         dll = inb(port + DLL);
 110         dlh = inb(port + DLH);
 111         outb(lcr, port + LCR);
 112         quot = (dlh << 8) | dll;
 113 
 114         return BASE_BAUD / quot;
 115 }
 116 
 117 static void parse_console_uart8250(void)
 118 {
 119         char optstr[64], *options;
 120         int baud = DEFAULT_BAUD;
 121         int port = 0;
 122 
 123         /*
 124          * console=uart8250,io,0x3f8,115200n8
 125          * need to make sure it is last one console !
 126          */
 127         if (cmdline_find_option("console", optstr, sizeof(optstr)) <= 0)
 128                 return;
 129 
 130         options = optstr;
 131 
 132         if (!strncmp(options, "uart8250,io,", 12))
 133                 port = simple_strtoull(options + 12, &options, 0);
 134         else if (!strncmp(options, "uart,io,", 8))
 135                 port = simple_strtoull(options + 8, &options, 0);
 136         else
 137                 return;
 138 
 139         if (options && (options[0] == ','))
 140                 baud = simple_strtoull(options + 1, &options, 0);
 141         else
 142                 baud = probe_baud(port);
 143 
 144         if (port)
 145                 early_serial_init(port, baud);
 146 }
 147 
 148 void console_init(void)
 149 {
 150         parse_earlyprintk();
 151 
 152         if (!early_serial_base)
 153                 parse_console_uart8250();
 154 }