1 /*
2  *  8250/16550-type serial ports prom_putchar()
3  *
4  *  Copyright (C) 2010  Yoichi Yuasa <yuasa@linux-mips.org>
5  *
6  *  This program is free software; you can redistribute it and/or modify
7  *  it under the terms of the GNU General Public License as published by
8  *  the Free Software Foundation; either version 2 of the License, or
9  *  (at your option) any later version.
10  *
11  *  This program is distributed in the hope that it will be useful,
12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  *  GNU General Public License for more details.
15  *
16  *  You should have received a copy of the GNU General Public License
17  *  along with this program; if not, write to the Free Software
18  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 #include <linux/io.h>
21 #include <linux/serial_core.h>
22 #include <linux/serial_reg.h>
23 
24 static void __iomem *serial8250_base;
25 static unsigned int serial8250_reg_shift;
26 static unsigned int serial8250_tx_timeout;
27 
28 void setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
29 				  unsigned int timeout)
30 {
31 	serial8250_base = (void __iomem *)base;
32 	serial8250_reg_shift = reg_shift;
33 	serial8250_tx_timeout = timeout;
34 }
35 
36 static inline u8 serial_in(int offset)
37 {
38 	return readb(serial8250_base + (offset << serial8250_reg_shift));
39 }
40 
41 static inline void serial_out(int offset, char value)
42 {
43 	writeb(value, serial8250_base + (offset << serial8250_reg_shift));
44 }
45 
46 void prom_putchar(char c)
47 {
48 	unsigned int timeout;
49 	int status, bits;
50 
51 	if (!serial8250_base)
52 		return;
53 
54 	timeout = serial8250_tx_timeout;
55 	bits = UART_LSR_TEMT | UART_LSR_THRE;
56 
57 	do {
58 		status = serial_in(UART_LSR);
59 
60 		if (--timeout == 0)
61 			break;
62 	} while ((status & bits) != bits);
63 
64 	if (timeout)
65 		serial_out(UART_TX, c);
66 }
67