1 // SPDX-License-Identifier: GPL-2.0
3 * Serial port routines for use during early boot reporting. This code is
4 * included from both the compressed kernel and the regular kernel.
8 #define DEFAULT_SERIAL_PORT 0x3f8 /* ttyS0 */
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 */
24 #define DEFAULT_BAUD 9600
26 static void early_serial_init(int port, int baud)
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 */
36 divisor = 115200 / baud;
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);
43 early_serial_base = port;
46 static void parse_earlyprintk(void)
48 int baud = DEFAULT_BAUD;
53 if (cmdline_find_option("earlyprintk", arg, sizeof(arg)) > 0) {
56 if (!strncmp(arg, "serial", 6)) {
57 port = DEFAULT_SERIAL_PORT;
66 * "serial,0x3f8,115200"
67 * "serial,ttyS0,115200"
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;
76 } else if (!strncmp(arg + pos, "ttyS", 4)) {
77 static const int bases[] = { 0x3f8, 0x2f8 };
80 /* += strlen("ttyS"); */
83 if (arg[pos++] == '1')
92 baud = simple_strtoull(arg + pos, &e, 0);
93 if (baud == 0 || arg + pos == e)
98 early_serial_init(port, baud);
101 #define BASE_BAUD (1843200/16)
102 static unsigned int probe_baud(int port)
104 unsigned char lcr, dll, dlh;
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;
114 return BASE_BAUD / quot;
117 static void parse_console_uart8250(void)
119 char optstr[64], *options;
120 int baud = DEFAULT_BAUD;
124 * console=uart8250,io,0x3f8,115200n8
125 * need to make sure it is last one console !
127 if (cmdline_find_option("console", optstr, sizeof(optstr)) <= 0)
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);
139 if (options && (options[0] == ','))
140 baud = simple_strtoull(options + 1, &options, 0);
142 baud = probe_baud(port);
145 early_serial_init(port, baud);
148 void console_init(void)
152 if (!early_serial_base)
153 parse_console_uart8250();