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
38unsigned 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_MEM32BE:
46		return ioread32be(port->membase + (offset << 2));
47	case UPIO_PORT:
48		return inb(port->iobase + offset);
49	default:
50		return 0;
51	}
52}
53
54void __weak __init serial8250_early_out(struct uart_port *port, int offset, int value)
55{
56	switch (port->iotype) {
57	case UPIO_MEM:
58		writeb(value, port->membase + offset);
59		break;
60	case UPIO_MEM32:
61		writel(value, port->membase + (offset << 2));
62		break;
63	case UPIO_MEM32BE:
64		iowrite32be(value, port->membase + (offset << 2));
65		break;
66	case UPIO_PORT:
67		outb(value, port->iobase + offset);
68		break;
69	}
70}
71
72#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
73
74static void __init wait_for_xmitr(struct uart_port *port)
75{
76	unsigned int status;
77
78	for (;;) {
79		status = serial8250_early_in(port, UART_LSR);
80		if ((status & BOTH_EMPTY) == BOTH_EMPTY)
81			return;
82		cpu_relax();
83	}
84}
85
86static void __init serial_putc(struct uart_port *port, int c)
87{
88	wait_for_xmitr(port);
89	serial8250_early_out(port, UART_TX, c);
90}
91
92static void __init early_serial8250_write(struct console *console,
93					const char *s, unsigned int count)
94{
95	struct earlycon_device *device = console->data;
96	struct uart_port *port = &device->port;
97	unsigned int ier;
98
99	/* Save the IER and disable interrupts preserving the UUE bit */
100	ier = serial8250_early_in(port, UART_IER);
101	if (ier)
102		serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
103
104	uart_console_write(port, s, count, serial_putc);
105
106	/* Wait for transmitter to become empty and restore the IER */
107	wait_for_xmitr(port);
108
109	if (ier)
110		serial8250_early_out(port, UART_IER, ier);
111}
112
113static void __init init_port(struct earlycon_device *device)
114{
115	struct uart_port *port = &device->port;
116	unsigned int divisor;
117	unsigned char c;
118	unsigned int ier;
119
120	serial8250_early_out(port, UART_LCR, 0x3);	/* 8n1 */
121	ier = serial8250_early_in(port, UART_IER);
122	serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
123	serial8250_early_out(port, UART_FCR, 0);	/* no fifo */
124	serial8250_early_out(port, UART_MCR, 0x3);	/* DTR + RTS */
125
126	divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
127	c = serial8250_early_in(port, UART_LCR);
128	serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
129	serial8250_early_out(port, UART_DLL, divisor & 0xff);
130	serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
131	serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
132}
133
134static int __init early_serial8250_setup(struct earlycon_device *device,
135					 const char *options)
136{
137	if (!(device->port.membase || device->port.iobase))
138		return -ENODEV;
139
140	if (!device->baud) {
141		struct uart_port *port = &device->port;
142		unsigned int ier;
143
144		/* assume the device was initialized, only mask interrupts */
145		ier = serial8250_early_in(port, UART_IER);
146		serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
147	} else
148		init_port(device);
149
150	device->con->write = early_serial8250_write;
151	return 0;
152}
153EARLYCON_DECLARE(uart8250, early_serial8250_setup);
154EARLYCON_DECLARE(uart, early_serial8250_setup);
155