1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * 8250/16550-type serial ports prom_putchar()
4 *
5 * Copyright (C) 2010 Yoichi Yuasa <yuasa@linux-mips.org>
6 */
7 #include <linux/io.h>
8 #include <linux/serial_core.h>
9 #include <linux/serial_reg.h>
10 #include <asm/setup.h>
11
12 static void __iomem *serial8250_base;
13 static unsigned int serial8250_reg_shift;
14 static unsigned int serial8250_tx_timeout;
15
16 void setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
17 unsigned int timeout)
18 {
19 serial8250_base = (void __iomem *)base;
20 serial8250_reg_shift = reg_shift;
21 serial8250_tx_timeout = timeout;
22 }
23
24 static inline u8 serial_in(int offset)
25 {
26 return readb(serial8250_base + (offset << serial8250_reg_shift));
27 }
28
29 static inline void serial_out(int offset, char value)
30 {
31 writeb(value, serial8250_base + (offset << serial8250_reg_shift));
32 }
33
34 void prom_putchar(char c)
35 {
36 unsigned int timeout;
37 int status, bits;
38
39 if (!serial8250_base)
40 return;
41
42 timeout = serial8250_tx_timeout;
43 bits = UART_LSR_TEMT | UART_LSR_THRE;
44
45 do {
46 status = serial_in(UART_LSR);
47
48 if (--timeout == 0)
49 break;
50 } while ((status & bits) != bits);
51
52 if (timeout)
53 serial_out(UART_TX, c);
54 }
55
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.