2 * Early serial console for 8250/16550 devices
4 * (c) Copyright 2004 Hewlett-Packard Development Company, L.P.
5 * Bjorn Helgaas <bjorn.helgaas@hp.com>
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
11 * Based on the 8250.c serial driver, Copyright (C) 2001 Russell King,
12 * and on early_printk.c by Andi Kleen.
14 * This is for use before the serial driver has initialized, in
15 * particular, before the UARTs have been discovered and named.
16 * Instead of specifying the console device as, e.g., "ttyS0",
17 * we locate the device directly by its MMIO or I/O port address.
19 * The user can specify the device directly, e.g.,
20 * earlycon=uart8250,io,0x3f8,9600n8
21 * earlycon=uart8250,mmio,0xff5e0000,115200n8
23 * console=uart8250,io,0x3f8,9600n8
24 * console=uart8250,mmio,0xff5e0000,115200n8
27 #include <linux/tty.h>
28 #include <linux/init.h>
29 #include <linux/console.h>
30 #include <linux/serial_core.h>
31 #include <linux/serial_reg.h>
32 #include <linux/serial.h>
33 #include <linux/serial_8250.h>
35 #include <asm/serial.h>
36 #ifdef CONFIG_FIX_EARLYCON_MEM
37 #include <asm/pgtable.h>
38 #include <asm/fixmap.h>
41 struct early_serial8250_device {
42 struct uart_port port;
43 char options[16]; /* e.g., 115200n8 */
47 static struct early_serial8250_device early_device;
49 static unsigned int __init serial_in(struct uart_port *port, int offset)
51 if (port->iotype == UPIO_MEM)
52 return readb(port->membase + offset);
54 return inb(port->iobase + offset);
57 static void __init serial_out(struct uart_port *port, int offset, int value)
59 if (port->iotype == UPIO_MEM)
60 writeb(value, port->membase + offset);
62 outb(value, port->iobase + offset);
65 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
67 static void __init wait_for_xmitr(struct uart_port *port)
72 status = serial_in(port, UART_LSR);
73 if ((status & BOTH_EMPTY) == BOTH_EMPTY)
79 static void __init serial_putc(struct uart_port *port, int c)
82 serial_out(port, UART_TX, c);
85 static void __init early_serial8250_write(struct console *console,
86 const char *s, unsigned int count)
88 struct uart_port *port = &early_device.port;
91 /* Save the IER and disable interrupts */
92 ier = serial_in(port, UART_IER);
93 serial_out(port, UART_IER, 0);
95 uart_console_write(port, s, count, serial_putc);
97 /* Wait for transmitter to become empty and restore the IER */
99 serial_out(port, UART_IER, ier);
102 static unsigned int __init probe_baud(struct uart_port *port)
104 unsigned char lcr, dll, dlm;
107 lcr = serial_in(port, UART_LCR);
108 serial_out(port, UART_LCR, lcr | UART_LCR_DLAB);
109 dll = serial_in(port, UART_DLL);
110 dlm = serial_in(port, UART_DLM);
111 serial_out(port, UART_LCR, lcr);
113 quot = (dlm << 8) | dll;
114 return (port->uartclk / 16) / quot;
117 static void __init init_port(struct early_serial8250_device *device)
119 struct uart_port *port = &device->port;
120 unsigned int divisor;
123 serial_out(port, UART_LCR, 0x3); /* 8n1 */
124 serial_out(port, UART_IER, 0); /* no interrupt */
125 serial_out(port, UART_FCR, 0); /* no fifo */
126 serial_out(port, UART_MCR, 0x3); /* DTR + RTS */
128 divisor = port->uartclk / (16 * device->baud);
129 c = serial_in(port, UART_LCR);
130 serial_out(port, UART_LCR, c | UART_LCR_DLAB);
131 serial_out(port, UART_DLL, divisor & 0xff);
132 serial_out(port, UART_DLM, (divisor >> 8) & 0xff);
133 serial_out(port, UART_LCR, c & ~UART_LCR_DLAB);
136 static int __init parse_options(struct early_serial8250_device *device,
139 struct uart_port *port = &device->port;
145 port->uartclk = BASE_BAUD * 16;
146 if (!strncmp(options, "mmio,", 5)) {
147 port->iotype = UPIO_MEM;
148 port->mapbase = simple_strtoul(options + 5, &options, 0);
149 #ifdef CONFIG_FIX_EARLYCON_MEM
150 set_fixmap_nocache(FIX_EARLYCON_MEM_BASE,
151 port->mapbase & PAGE_MASK);
153 (void __iomem *)__fix_to_virt(FIX_EARLYCON_MEM_BASE);
154 port->membase += port->mapbase & ~PAGE_MASK;
156 port->membase = ioremap_nocache(port->mapbase, 64);
157 if (!port->membase) {
158 printk(KERN_ERR "%s: Couldn't ioremap 0x%llx\n",
160 (unsigned long long)port->mapbase);
165 } else if (!strncmp(options, "io,", 3)) {
166 port->iotype = UPIO_PORT;
167 port->iobase = simple_strtoul(options + 3, &options, 0);
172 options = strchr(options, ',');
175 device->baud = simple_strtoul(options, NULL, 0);
176 length = min(strcspn(options, " "), sizeof(device->options));
177 strncpy(device->options, options, length);
179 device->baud = probe_baud(port);
180 snprintf(device->options, sizeof(device->options), "%u",
184 printk(KERN_INFO "Early serial console at %s 0x%llx (options '%s')\n",
185 mmio ? "MMIO" : "I/O port",
186 mmio ? (unsigned long long) port->mapbase
187 : (unsigned long long) port->iobase,
192 static struct console early_serial8250_console __initdata = {
194 .write = early_serial8250_write,
195 .flags = CON_PRINTBUFFER | CON_BOOT,
199 static int __init early_serial8250_setup(char *options)
201 struct early_serial8250_device *device = &early_device;
204 if (device->port.membase || device->port.iobase)
207 err = parse_options(device, options);
215 int __init setup_early_serial8250_console(char *cmdline)
220 options = strstr(cmdline, "uart8250,");
222 options = strstr(cmdline, "uart,");
227 options = strchr(cmdline, ',') + 1;
228 err = early_serial8250_setup(options);
232 register_console(&early_serial8250_console);
237 int serial8250_find_port_for_earlycon(void)
239 struct early_serial8250_device *device = &early_device;
240 struct uart_port *port = &device->port;
244 if (!device->port.membase && !device->port.iobase)
247 line = serial8250_find_port(port);
251 ret = update_console_cmdline("uart", 8250,
252 "ttyS", line, device->options);
254 ret = update_console_cmdline("uart", 0,
255 "ttyS", line, device->options);
260 early_param("earlycon", setup_early_serial8250_console);