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
22 * earlycon=uart8250,mmio32,0xff5e0000,115200n8
24 * console=uart8250,io,0x3f8,9600n8
25 * console=uart8250,mmio,0xff5e0000,115200n8
26 * console=uart8250,mmio32,0xff5e0000,115200n8
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>
36 #include <asm/serial.h>
38 unsigned int __weak __init serial8250_early_in(struct uart_port *port, int offset)
40 switch (port->iotype) {
42 return readb(port->membase + offset);
44 return readl(port->membase + (offset << 2));
46 return inb(port->iobase + offset);
52 void __weak __init serial8250_early_out(struct uart_port *port, int offset, int value)
54 switch (port->iotype) {
56 writeb(value, port->membase + offset);
59 writel(value, port->membase + (offset << 2));
62 outb(value, port->iobase + offset);
67 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
69 static void __init wait_for_xmitr(struct uart_port *port)
74 status = serial8250_early_in(port, UART_LSR);
75 if ((status & BOTH_EMPTY) == BOTH_EMPTY)
81 static void __init serial_putc(struct uart_port *port, int c)
84 serial8250_early_out(port, UART_TX, c);
87 static void __init early_serial8250_write(struct console *console,
88 const char *s, unsigned int count)
90 struct earlycon_device *device = console->data;
91 struct uart_port *port = &device->port;
94 /* Save the IER and disable interrupts preserving the UUE bit */
95 ier = serial8250_early_in(port, UART_IER);
97 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
99 uart_console_write(port, s, count, serial_putc);
101 /* Wait for transmitter to become empty and restore the IER */
102 wait_for_xmitr(port);
105 serial8250_early_out(port, UART_IER, ier);
108 static unsigned int __init probe_baud(struct uart_port *port)
110 unsigned char lcr, dll, dlm;
113 lcr = serial8250_early_in(port, UART_LCR);
114 serial8250_early_out(port, UART_LCR, lcr | UART_LCR_DLAB);
115 dll = serial8250_early_in(port, UART_DLL);
116 dlm = serial8250_early_in(port, UART_DLM);
117 serial8250_early_out(port, UART_LCR, lcr);
119 quot = (dlm << 8) | dll;
120 return (port->uartclk / 16) / quot;
123 static void __init init_port(struct earlycon_device *device)
125 struct uart_port *port = &device->port;
126 unsigned int divisor;
130 serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */
131 ier = serial8250_early_in(port, UART_IER);
132 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
133 serial8250_early_out(port, UART_FCR, 0); /* no fifo */
134 serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */
136 divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
137 c = serial8250_early_in(port, UART_LCR);
138 serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
139 serial8250_early_out(port, UART_DLL, divisor & 0xff);
140 serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
141 serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
144 static int __init early_serial8250_setup(struct earlycon_device *device,
147 if (!(device->port.membase || device->port.iobase))
151 struct uart_port *port = &device->port;
154 device->baud = probe_baud(&device->port);
155 snprintf(device->options, sizeof(device->options), "%u",
158 /* assume the device was initialized, only mask interrupts */
159 ier = serial8250_early_in(port, UART_IER);
160 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
164 device->con->write = early_serial8250_write;
167 EARLYCON_DECLARE(uart8250, early_serial8250_setup);
168 EARLYCON_DECLARE(uart, early_serial8250_setup);