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 void __init
init_port(struct earlycon_device
*device
)
110 struct uart_port
*port
= &device
->port
;
111 unsigned int divisor
;
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 */
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
);
129 static int __init
early_serial8250_setup(struct earlycon_device
*device
,
132 if (!(device
->port
.membase
|| device
->port
.iobase
))
136 struct uart_port
*port
= &device
->port
;
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
);
145 device
->con
->write
= early_serial8250_write
;
148 EARLYCON_DECLARE(uart8250
, early_serial8250_setup
);
149 EARLYCON_DECLARE(uart
, early_serial8250_setup
);
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