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/of.h> 33 #include <linux/of_device.h> 34 #include <linux/serial_reg.h> 35 #include <linux/serial.h> 36 #include <linux/serial_8250.h> 37 #include <asm/io.h> 38 #include <asm/serial.h> 39 40 static unsigned int __init serial8250_early_in(struct uart_port *port, int offset) 41 { 42 switch (port->iotype) { 43 case UPIO_MEM: 44 return readb(port->membase + offset); 45 case UPIO_MEM16: 46 return readw(port->membase + (offset << 1)); 47 case UPIO_MEM32: 48 return readl(port->membase + (offset << 2)); 49 case UPIO_MEM32BE: 50 return ioread32be(port->membase + (offset << 2)); 51 case UPIO_PORT: 52 return inb(port->iobase + offset); 53 default: 54 return 0; 55 } 56 } 57 58 static void __init serial8250_early_out(struct uart_port *port, int offset, int value) 59 { 60 switch (port->iotype) { 61 case UPIO_MEM: 62 writeb(value, port->membase + offset); 63 break; 64 case UPIO_MEM16: 65 writew(value, port->membase + (offset << 1)); 66 break; 67 case UPIO_MEM32: 68 writel(value, port->membase + (offset << 2)); 69 break; 70 case UPIO_MEM32BE: 71 iowrite32be(value, port->membase + (offset << 2)); 72 break; 73 case UPIO_PORT: 74 outb(value, port->iobase + offset); 75 break; 76 } 77 } 78 79 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE) 80 81 static void __init serial_putc(struct uart_port *port, int c) 82 { 83 unsigned int status; 84 85 serial8250_early_out(port, UART_TX, c); 86 87 for (;;) { 88 status = serial8250_early_in(port, UART_LSR); 89 if ((status & BOTH_EMPTY) == BOTH_EMPTY) 90 break; 91 cpu_relax(); 92 } 93 } 94 95 static void __init early_serial8250_write(struct console *console, 96 const char *s, unsigned int count) 97 { 98 struct earlycon_device *device = console->data; 99 struct uart_port *port = &device->port; 100 101 uart_console_write(port, s, count, serial_putc); 102 } 103 104 static void __init init_port(struct earlycon_device *device) 105 { 106 struct uart_port *port = &device->port; 107 unsigned int divisor; 108 unsigned char c; 109 unsigned int ier; 110 111 serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */ 112 ier = serial8250_early_in(port, UART_IER); 113 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */ 114 serial8250_early_out(port, UART_FCR, 0); /* no fifo */ 115 serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */ 116 117 divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud); 118 c = serial8250_early_in(port, UART_LCR); 119 serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB); 120 serial8250_early_out(port, UART_DLL, divisor & 0xff); 121 serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff); 122 serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB); 123 } 124 125 int __init early_serial8250_setup(struct earlycon_device *device, 126 const char *options) 127 { 128 if (!(device->port.membase || device->port.iobase)) 129 return -ENODEV; 130 131 if (!device->baud) { 132 struct uart_port *port = &device->port; 133 unsigned int ier; 134 135 /* assume the device was initialized, only mask interrupts */ 136 ier = serial8250_early_in(port, UART_IER); 137 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); 138 } else 139 init_port(device); 140 141 device->con->write = early_serial8250_write; 142 return 0; 143 } 144 EARLYCON_DECLARE(uart8250, early_serial8250_setup); 145 EARLYCON_DECLARE(uart, early_serial8250_setup); 146 OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup); 147 OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup); 148