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_MEM32: 46 return readl(port->membase + (offset << 2)); 47 case UPIO_MEM32BE: 48 return ioread32be(port->membase + (offset << 2)); 49 case UPIO_PORT: 50 return inb(port->iobase + offset); 51 default: 52 return 0; 53 } 54 } 55 56 static void __init serial8250_early_out(struct uart_port *port, int offset, int value) 57 { 58 switch (port->iotype) { 59 case UPIO_MEM: 60 writeb(value, port->membase + offset); 61 break; 62 case UPIO_MEM32: 63 writel(value, port->membase + (offset << 2)); 64 break; 65 case UPIO_MEM32BE: 66 iowrite32be(value, port->membase + (offset << 2)); 67 break; 68 case UPIO_PORT: 69 outb(value, port->iobase + offset); 70 break; 71 } 72 } 73 74 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE) 75 76 static void __init wait_for_xmitr(struct uart_port *port) 77 { 78 unsigned int status; 79 80 for (;;) { 81 status = serial8250_early_in(port, UART_LSR); 82 if ((status & BOTH_EMPTY) == BOTH_EMPTY) 83 return; 84 cpu_relax(); 85 } 86 } 87 88 static void __init serial_putc(struct uart_port *port, int c) 89 { 90 wait_for_xmitr(port); 91 serial8250_early_out(port, UART_TX, c); 92 } 93 94 static void __init early_serial8250_write(struct console *console, 95 const char *s, unsigned int count) 96 { 97 struct earlycon_device *device = console->data; 98 struct uart_port *port = &device->port; 99 unsigned int ier; 100 101 /* Save the IER and disable interrupts preserving the UUE bit */ 102 ier = serial8250_early_in(port, UART_IER); 103 if (ier) 104 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); 105 106 uart_console_write(port, s, count, serial_putc); 107 108 /* Wait for transmitter to become empty and restore the IER */ 109 wait_for_xmitr(port); 110 111 if (ier) 112 serial8250_early_out(port, UART_IER, ier); 113 } 114 115 static void __init init_port(struct earlycon_device *device) 116 { 117 struct uart_port *port = &device->port; 118 unsigned int divisor; 119 unsigned char c; 120 unsigned int ier; 121 122 serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */ 123 ier = serial8250_early_in(port, UART_IER); 124 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */ 125 serial8250_early_out(port, UART_FCR, 0); /* no fifo */ 126 serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */ 127 128 divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud); 129 c = serial8250_early_in(port, UART_LCR); 130 serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB); 131 serial8250_early_out(port, UART_DLL, divisor & 0xff); 132 serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff); 133 serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB); 134 } 135 136 int __init early_serial8250_setup(struct earlycon_device *device, 137 const char *options) 138 { 139 if (!(device->port.membase || device->port.iobase)) 140 return -ENODEV; 141 142 if (!device->baud) { 143 struct uart_port *port = &device->port; 144 unsigned int ier; 145 146 /* assume the device was initialized, only mask interrupts */ 147 ier = serial8250_early_in(port, UART_IER); 148 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); 149 } else 150 init_port(device); 151 152 device->con->write = early_serial8250_write; 153 return 0; 154 } 155 EARLYCON_DECLARE(uart8250, early_serial8250_setup); 156 EARLYCON_DECLARE(uart, early_serial8250_setup); 157 OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup); 158 OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup); 159