xref: /linux/arch/x86/boot/early_serial_console.c (revision 3eb66e91a25497065c5322b1268cbc3953642227)
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 
early_serial_init(int port,int baud)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 
parse_earlyprintk(void)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)
probe_baud(int port)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 
parse_console_uart8250(void)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 
console_init(void)148 void console_init(void)
149 {
150 	parse_earlyprintk();
151 
152 	if (!early_serial_base)
153 		parse_console_uart8250();
154 }
155