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
serial8250_early_in(struct uart_port * port,int offset)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
serial8250_early_out(struct uart_port * port,int offset,int value)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
wait_for_xmitr(struct uart_port * port)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
serial_putc(struct uart_port * port,int c)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
early_serial8250_write(struct console * console,const char * s,unsigned int count)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
init_port(struct earlycon_device * device)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
early_serial8250_setup(struct earlycon_device * device,const char * options)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