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
40static 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
56static 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
76static 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
88static 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
94static 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
115static 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
136int __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}
155EARLYCON_DECLARE(uart8250, early_serial8250_setup);
156EARLYCON_DECLARE(uart, early_serial8250_setup);
157OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
158OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
159