1 /*
2  * A udbg backend which logs messages and reads input from in memory
3  * buffers.
4  *
5  * The console output can be read from memcons_output which is a
6  * circular buffer whose next write position is stored in memcons.output_pos.
7  *
8  * Input may be passed by writing into the memcons_input buffer when it is
9  * empty. The input buffer is empty when both input_pos == input_start and
10  * *input_start == '\0'.
11  *
12  * Copyright (C) 2003-2005 Anton Blanchard and Milton Miller, IBM Corp
13  * Copyright (C) 2013 Alistair Popple, IBM Corp
14  *
15  *      This program is free software; you can redistribute it and/or
16  *      modify it under the terms of the GNU General Public License
17  *      as published by the Free Software Foundation; either version
18  *      2 of the License, or (at your option) any later version.
19  */
20 
21 #include <linux/init.h>
22 #include <linux/kernel.h>
23 #include <asm/barrier.h>
24 #include <asm/page.h>
25 #include <asm/processor.h>
26 #include <asm/udbg.h>
27 
28 struct memcons {
29 	char *output_start;
30 	char *output_pos;
31 	char *output_end;
32 	char *input_start;
33 	char *input_pos;
34 	char *input_end;
35 };
36 
37 static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
38 static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
39 
40 struct memcons memcons = {
41 	.output_start = memcons_output,
42 	.output_pos = memcons_output,
43 	.output_end = &memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE],
44 	.input_start = memcons_input,
45 	.input_pos = memcons_input,
46 	.input_end = &memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE],
47 };
48 
49 void memcons_putc(char c)
50 {
51 	char *new_output_pos;
52 
53 	*memcons.output_pos = c;
54 	wmb();
55 	new_output_pos = memcons.output_pos + 1;
56 	if (new_output_pos >= memcons.output_end)
57 		new_output_pos = memcons.output_start;
58 
59 	memcons.output_pos = new_output_pos;
60 }
61 
62 int memcons_getc_poll(void)
63 {
64 	char c;
65 	char *new_input_pos;
66 
67 	if (*memcons.input_pos) {
68 		c = *memcons.input_pos;
69 
70 		new_input_pos = memcons.input_pos + 1;
71 		if (new_input_pos >= memcons.input_end)
72 			new_input_pos = memcons.input_start;
73 		else if (*new_input_pos == '\0')
74 			new_input_pos = memcons.input_start;
75 
76 		*memcons.input_pos = '\0';
77 		wmb();
78 		memcons.input_pos = new_input_pos;
79 		return c;
80 	}
81 
82 	return -1;
83 }
84 
85 int memcons_getc(void)
86 {
87 	int c;
88 
89 	while (1) {
90 		c = memcons_getc_poll();
91 		if (c == -1)
92 			cpu_relax();
93 		else
94 			break;
95 	}
96 
97 	return c;
98 }
99 
100 void udbg_init_memcons(void)
101 {
102 	udbg_putc = memcons_putc;
103 	udbg_getc = memcons_getc;
104 	udbg_getc_poll = memcons_getc_poll;
105 }
106