1 /* 2 * Early serial console for 8250/16550 devices 3 * 4 * (c) Copyright 2004 Hewlett-Packard Development Company, L.P. 5 * Bjorn Helgaas <bjorn.helgaas@hp.com> 6 * 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. 10 * 11 * Based on the 8250.c serial driver, Copyright (C) 2001 Russell King, 12 * and on early_printk.c by Andi Kleen. 13 * 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. 18 * 19 * The user can specify the device directly, e.g., 20 * earlycon=uart8250,io,0x3f8,9600n8 21 * earlycon=uart8250,mmio,0xff5e0000,115200n8 22 * earlycon=uart8250,mmio32,0xff5e0000,115200n8 23 * or 24 * console=uart8250,io,0x3f8,9600n8 25 * console=uart8250,mmio,0xff5e0000,115200n8 26 * console=uart8250,mmio32,0xff5e0000,115200n8 27 */ 28 29 #include <linux/tty.h> 30 #include <linux/init.h> 31 #include <linux/console.h> 32 #include <linux/serial_core.h> 33 #include <linux/serial_reg.h> 34 #include <linux/serial.h> 35 #include <linux/serial_8250.h> 36 #include <asm/io.h> 37 #include <asm/serial.h> 38 39 static struct earlycon_device *early_device; 40 41 unsigned int __weak __init serial8250_early_in(struct uart_port *port, int offset) 42 { 43 switch (port->iotype) { 44 case UPIO_MEM: 45 return readb(port->membase + offset); 46 case UPIO_MEM32: 47 return readl(port->membase + (offset << 2)); 48 case UPIO_PORT: 49 return inb(port->iobase + offset); 50 default: 51 return 0; 52 } 53 } 54 55 void __weak __init serial8250_early_out(struct uart_port *port, int offset, int value) 56 { 57 switch (port->iotype) { 58 case UPIO_MEM: 59 writeb(value, port->membase + offset); 60 break; 61 case UPIO_MEM32: 62 writel(value, port->membase + (offset << 2)); 63 break; 64 case UPIO_PORT: 65 outb(value, port->iobase + offset); 66 break; 67 } 68 } 69 70 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE) 71 72 static void __init wait_for_xmitr(struct uart_port *port) 73 { 74 unsigned int status; 75 76 for (;;) { 77 status = serial8250_early_in(port, UART_LSR); 78 if ((status & BOTH_EMPTY) == BOTH_EMPTY) 79 return; 80 cpu_relax(); 81 } 82 } 83 84 static void __init serial_putc(struct uart_port *port, int c) 85 { 86 wait_for_xmitr(port); 87 serial8250_early_out(port, UART_TX, c); 88 } 89 90 static void __init early_serial8250_write(struct console *console, 91 const char *s, unsigned int count) 92 { 93 struct uart_port *port = &early_device->port; 94 unsigned int ier; 95 96 /* Save the IER and disable interrupts */ 97 ier = serial8250_early_in(port, UART_IER); 98 serial8250_early_out(port, UART_IER, 0); 99 100 uart_console_write(port, s, count, serial_putc); 101 102 /* Wait for transmitter to become empty and restore the IER */ 103 wait_for_xmitr(port); 104 serial8250_early_out(port, UART_IER, ier); 105 } 106 107 static unsigned int __init probe_baud(struct uart_port *port) 108 { 109 unsigned char lcr, dll, dlm; 110 unsigned int quot; 111 112 lcr = serial8250_early_in(port, UART_LCR); 113 serial8250_early_out(port, UART_LCR, lcr | UART_LCR_DLAB); 114 dll = serial8250_early_in(port, UART_DLL); 115 dlm = serial8250_early_in(port, UART_DLM); 116 serial8250_early_out(port, UART_LCR, lcr); 117 118 quot = (dlm << 8) | dll; 119 return (port->uartclk / 16) / quot; 120 } 121 122 static void __init init_port(struct earlycon_device *device) 123 { 124 struct uart_port *port = &device->port; 125 unsigned int divisor; 126 unsigned char c; 127 128 serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */ 129 serial8250_early_out(port, UART_IER, 0); /* no interrupt */ 130 serial8250_early_out(port, UART_FCR, 0); /* no fifo */ 131 serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */ 132 133 divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud); 134 c = serial8250_early_in(port, UART_LCR); 135 serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB); 136 serial8250_early_out(port, UART_DLL, divisor & 0xff); 137 serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff); 138 serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB); 139 } 140 141 static int __init early_serial8250_setup(struct earlycon_device *device, 142 const char *options) 143 { 144 if (!(device->port.membase || device->port.iobase)) 145 return 0; 146 147 if (!device->baud) { 148 device->baud = probe_baud(&device->port); 149 snprintf(device->options, sizeof(device->options), "%u", 150 device->baud); 151 } 152 153 init_port(device); 154 155 early_device = device; 156 device->con->write = early_serial8250_write; 157 return 0; 158 } 159 EARLYCON_DECLARE(uart8250, early_serial8250_setup); 160 EARLYCON_DECLARE(uart, early_serial8250_setup); 161 162 int __init setup_early_serial8250_console(char *cmdline) 163 { 164 char match[] = "uart8250"; 165 166 if (cmdline && cmdline[4] == ',') 167 match[4] = '\0'; 168 169 return setup_earlycon(cmdline, match, early_serial8250_setup); 170 } 171 172 int serial8250_find_port_for_earlycon(void) 173 { 174 struct earlycon_device *device = early_device; 175 struct uart_port *port = device ? &device->port : NULL; 176 int line; 177 int ret; 178 179 if (!port || (!port->membase && !port->iobase)) 180 return -ENODEV; 181 182 line = serial8250_find_port(port); 183 if (line < 0) 184 return -ENODEV; 185 186 ret = update_console_cmdline("uart", 8250, 187 "ttyS", line, device->options); 188 if (ret < 0) 189 ret = update_console_cmdline("uart", 0, 190 "ttyS", line, device->options); 191 192 return ret; 193 } 194