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_core.h>
33 #include <linux/serial_reg.h>
34 #include <linux/serial.h>
35 #include <linux/serial_8250.h>
37 #include <asm/serial.h>
39 static struct earlycon_device
*early_device
;
41 unsigned int __weak __init
serial8250_early_in(struct uart_port
*port
, int offset
)
43 switch (port
->iotype
) {
45 return readb(port
->membase
+ offset
);
47 return readl(port
->membase
+ (offset
<< 2));
49 return inb(port
->iobase
+ offset
);
55 void __weak __init
serial8250_early_out(struct uart_port
*port
, int offset
, int value
)
57 switch (port
->iotype
) {
59 writeb(value
, port
->membase
+ offset
);
62 writel(value
, port
->membase
+ (offset
<< 2));
65 outb(value
, port
->iobase
+ offset
);
70 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
72 static void __init
wait_for_xmitr(struct uart_port
*port
)
77 status
= serial8250_early_in(port
, UART_LSR
);
78 if ((status
& BOTH_EMPTY
) == BOTH_EMPTY
)
84 static void __init
serial_putc(struct uart_port
*port
, int c
)
87 serial8250_early_out(port
, UART_TX
, c
);
90 static void __init
early_serial8250_write(struct console
*console
,
91 const char *s
, unsigned int count
)
93 struct uart_port
*port
= &early_device
->port
;
96 /* Save the IER and disable interrupts preserving the UUE bit */
97 ier
= serial8250_early_in(port
, UART_IER
);
99 serial8250_early_out(port
, UART_IER
, ier
& UART_IER_UUE
);
101 uart_console_write(port
, s
, count
, serial_putc
);
103 /* Wait for transmitter to become empty and restore the IER */
104 wait_for_xmitr(port
);
107 serial8250_early_out(port
, UART_IER
, ier
);
110 static unsigned int __init
probe_baud(struct uart_port
*port
)
112 unsigned char lcr
, dll
, dlm
;
115 lcr
= serial8250_early_in(port
, UART_LCR
);
116 serial8250_early_out(port
, UART_LCR
, lcr
| UART_LCR_DLAB
);
117 dll
= serial8250_early_in(port
, UART_DLL
);
118 dlm
= serial8250_early_in(port
, UART_DLM
);
119 serial8250_early_out(port
, UART_LCR
, lcr
);
121 quot
= (dlm
<< 8) | dll
;
122 return (port
->uartclk
/ 16) / quot
;
125 static void __init
init_port(struct earlycon_device
*device
)
127 struct uart_port
*port
= &device
->port
;
128 unsigned int divisor
;
132 serial8250_early_out(port
, UART_LCR
, 0x3); /* 8n1 */
133 ier
= serial8250_early_in(port
, UART_IER
);
134 serial8250_early_out(port
, UART_IER
, ier
& UART_IER_UUE
); /* no interrupt */
135 serial8250_early_out(port
, UART_FCR
, 0); /* no fifo */
136 serial8250_early_out(port
, UART_MCR
, 0x3); /* DTR + RTS */
138 divisor
= DIV_ROUND_CLOSEST(port
->uartclk
, 16 * device
->baud
);
139 c
= serial8250_early_in(port
, UART_LCR
);
140 serial8250_early_out(port
, UART_LCR
, c
| UART_LCR_DLAB
);
141 serial8250_early_out(port
, UART_DLL
, divisor
& 0xff);
142 serial8250_early_out(port
, UART_DLM
, (divisor
>> 8) & 0xff);
143 serial8250_early_out(port
, UART_LCR
, c
& ~UART_LCR_DLAB
);
146 static int __init
early_serial8250_setup(struct earlycon_device
*device
,
149 if (!(device
->port
.membase
|| device
->port
.iobase
))
153 device
->baud
= probe_baud(&device
->port
);
154 snprintf(device
->options
, sizeof(device
->options
), "%u",
160 early_device
= device
;
161 device
->con
->write
= early_serial8250_write
;
164 EARLYCON_DECLARE(uart8250
, early_serial8250_setup
);
165 EARLYCON_DECLARE(uart
, early_serial8250_setup
);
167 int __init
setup_early_serial8250_console(char *cmdline
)
169 char match
[] = "uart8250";
171 if (cmdline
&& cmdline
[4] == ',')
174 return setup_earlycon(cmdline
, match
, early_serial8250_setup
);
177 int serial8250_find_port_for_earlycon(void)
179 struct earlycon_device
*device
= early_device
;
180 struct uart_port
*port
= device
? &device
->port
: NULL
;
184 if (!port
|| (!port
->membase
&& !port
->iobase
))
187 line
= serial8250_find_port(port
);
191 ret
= update_console_cmdline("uart", 8250,
192 "ttyS", line
, device
->options
);
194 ret
= update_console_cmdline("uart", 0,
195 "ttyS", line
, device
->options
);
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