tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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 offset <<= port->regshift;
43
44 switch (port->iotype) {
45 case UPIO_MEM:
46 return readb(port->membase + offset);
47 case UPIO_MEM16:
48 return readw(port->membase + offset);
49 case UPIO_MEM32:
50 return readl(port->membase + offset);
51 case UPIO_MEM32BE:
52 return ioread32be(port->membase + offset);
53 case UPIO_PORT:
54 return inb(port->iobase + offset);
55 default:
56 return 0;
57 }
58}
59
60static void __init serial8250_early_out(struct uart_port *port, int offset, int value)
61{
62 offset <<= port->regshift;
63
64 switch (port->iotype) {
65 case UPIO_MEM:
66 writeb(value, port->membase + offset);
67 break;
68 case UPIO_MEM16:
69 writew(value, port->membase + offset);
70 break;
71 case UPIO_MEM32:
72 writel(value, port->membase + offset);
73 break;
74 case UPIO_MEM32BE:
75 iowrite32be(value, port->membase + offset);
76 break;
77 case UPIO_PORT:
78 outb(value, port->iobase + offset);
79 break;
80 }
81}
82
83#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
84
85static void __init serial_putc(struct uart_port *port, int c)
86{
87 unsigned int status;
88
89 serial8250_early_out(port, UART_TX, c);
90
91 for (;;) {
92 status = serial8250_early_in(port, UART_LSR);
93 if ((status & BOTH_EMPTY) == BOTH_EMPTY)
94 break;
95 cpu_relax();
96 }
97}
98
99static void __init early_serial8250_write(struct console *console,
100 const char *s, unsigned int count)
101{
102 struct earlycon_device *device = console->data;
103 struct uart_port *port = &device->port;
104
105 uart_console_write(port, s, count, serial_putc);
106}
107
108static void __init init_port(struct earlycon_device *device)
109{
110 struct uart_port *port = &device->port;
111 unsigned int divisor;
112 unsigned char c;
113 unsigned int ier;
114
115 serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */
116 ier = serial8250_early_in(port, UART_IER);
117 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
118 serial8250_early_out(port, UART_FCR, 0); /* no fifo */
119 serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */
120
121 divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
122 c = serial8250_early_in(port, UART_LCR);
123 serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
124 serial8250_early_out(port, UART_DLL, divisor & 0xff);
125 serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
126 serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
127}
128
129int __init early_serial8250_setup(struct earlycon_device *device,
130 const char *options)
131{
132 if (!(device->port.membase || device->port.iobase))
133 return -ENODEV;
134
135 if (!device->baud) {
136 struct uart_port *port = &device->port;
137 unsigned int ier;
138
139 /* assume the device was initialized, only mask interrupts */
140 ier = serial8250_early_in(port, UART_IER);
141 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
142 } else
143 init_port(device);
144
145 device->con->write = early_serial8250_write;
146 return 0;
147}
148EARLYCON_DECLARE(uart8250, early_serial8250_setup);
149EARLYCON_DECLARE(uart, early_serial8250_setup);
150OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
151OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
152OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
153
154#ifdef CONFIG_SERIAL_8250_OMAP
155
156static int __init early_omap8250_setup(struct earlycon_device *device,
157 const char *options)
158{
159 struct uart_port *port = &device->port;
160
161 if (!(device->port.membase || device->port.iobase))
162 return -ENODEV;
163
164 port->regshift = 2;
165 device->con->write = early_serial8250_write;
166 return 0;
167}
168
169OF_EARLYCON_DECLARE(omap8250, "ti,omap2-uart", early_omap8250_setup);
170OF_EARLYCON_DECLARE(omap8250, "ti,omap3-uart", early_omap8250_setup);
171OF_EARLYCON_DECLARE(omap8250, "ti,omap4-uart", early_omap8250_setup);
172
173#endif