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_reg.h> 33 #include <linux/serial.h> 34 #include <linux/serial_8250.h> 35 #include <asm/io.h> 36 #include <asm/serial.h> 37 38 unsigned int __weak __init serial8250_early_in(struct uart_port *port, int offset) 39 { 40 switch (port->iotype) { 41 case UPIO_MEM: 42 return readb(port->membase + offset); 43 case UPIO_MEM32: 44 return readl(port->membase + (offset << 2)); 45 case UPIO_PORT: 46 return inb(port->iobase + offset); 47 default: 48 return 0; 49 } 50 } 51 52 void __weak __init serial8250_early_out(struct uart_port *port, int offset, int value) 53 { 54 switch (port->iotype) { 55 case UPIO_MEM: 56 writeb(value, port->membase + offset); 57 break; 58 case UPIO_MEM32: 59 writel(value, port->membase + (offset << 2)); 60 break; 61 case UPIO_PORT: 62 outb(value, port->iobase + offset); 63 break; 64 } 65 } 66 67 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE) 68 69 static void __init wait_for_xmitr(struct uart_port *port) 70 { 71 unsigned int status; 72 73 for (;;) { 74 status = serial8250_early_in(port, UART_LSR); 75 if ((status & BOTH_EMPTY) == BOTH_EMPTY) 76 return; 77 cpu_relax(); 78 } 79 } 80 81 static void __init serial_putc(struct uart_port *port, int c) 82 { 83 wait_for_xmitr(port); 84 serial8250_early_out(port, UART_TX, c); 85 } 86 87 static void __init early_serial8250_write(struct console *console, 88 const char *s, unsigned int count) 89 { 90 struct earlycon_device *device = console->data; 91 struct uart_port *port = &device->port; 92 unsigned int ier; 93 94 /* Save the IER and disable interrupts preserving the UUE bit */ 95 ier = serial8250_early_in(port, UART_IER); 96 if (ier) 97 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); 98 99 uart_console_write(port, s, count, serial_putc); 100 101 /* Wait for transmitter to become empty and restore the IER */ 102 wait_for_xmitr(port); 103 104 if (ier) 105 serial8250_early_out(port, UART_IER, ier); 106 } 107 108 static void __init init_port(struct earlycon_device *device) 109 { 110 struct uart_port *port = &device->port; 111 unsigned int divisor; 112 unsigned char c; 113 unsigned int ier; 114 115 serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */ 116 ier = serial8250_early_in(port, UART_IER); 117 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */ 118 serial8250_early_out(port, UART_FCR, 0); /* no fifo */ 119 serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */ 120 121 divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud); 122 c = serial8250_early_in(port, UART_LCR); 123 serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB); 124 serial8250_early_out(port, UART_DLL, divisor & 0xff); 125 serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff); 126 serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB); 127 } 128 129 static int __init early_serial8250_setup(struct earlycon_device *device, 130 const char *options) 131 { 132 if (!(device->port.membase || device->port.iobase)) 133 return -ENODEV; 134 135 if (!device->baud) { 136 struct uart_port *port = &device->port; 137 unsigned int ier; 138 139 /* assume the device was initialized, only mask interrupts */ 140 ier = serial8250_early_in(port, UART_IER); 141 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); 142 } else 143 init_port(device); 144 145 device->con->write = early_serial8250_write; 146 return 0; 147 } 148 EARLYCON_DECLARE(uart8250, early_serial8250_setup); 149 EARLYCON_DECLARE(uart, early_serial8250_setup); 150