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/kernel.h>
22 #include <asm/barrier.h>
23 #include <asm/page.h>
24 #include <asm/processor.h>
25 #include <asm/udbg.h>
26 
27 struct memcons {
28 	char *output_start;
29 	char *output_pos;
30 	char *output_end;
31 	char *input_start;
32 	char *input_pos;
33 	char *input_end;
34 };
35 
36 static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
37 static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
38 
39 struct memcons memcons = {
40 	.output_start = memcons_output,
41 	.output_pos = memcons_output,
42 	.output_end = &memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE],
43 	.input_start = memcons_input,
44 	.input_pos = memcons_input,
45 	.input_end = &memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE],
46 };
47 
48 void memcons_putc(char c)
49 {
50 	char *new_output_pos;
51 
52 	*memcons.output_pos = c;
53 	wmb();
54 	new_output_pos = memcons.output_pos + 1;
55 	if (new_output_pos >= memcons.output_end)
56 		new_output_pos = memcons.output_start;
57 
58 	memcons.output_pos = new_output_pos;
59 }
60 
61 int memcons_getc_poll(void)
62 {
63 	char c;
64 	char *new_input_pos;
65 
66 	if (*memcons.input_pos) {
67 		c = *memcons.input_pos;
68 
69 		new_input_pos = memcons.input_pos + 1;
70 		if (new_input_pos >= memcons.input_end)
71 			new_input_pos = memcons.input_start;
72 		else if (*new_input_pos == '\0')
73 			new_input_pos = memcons.input_start;
74 
75 		*memcons.input_pos = '\0';
76 		wmb();
77 		memcons.input_pos = new_input_pos;
78 		return c;
79 	}
80 
81 	return -1;
82 }
83 
84 int memcons_getc(void)
85 {
86 	int c;
87 
88 	while (1) {
89 		c = memcons_getc_poll();
90 		if (c == -1)
91 			cpu_relax();
92 		else
93 			break;
94 	}
95 
96 	return c;
97 }
98 
99 void udbg_init_memcons(void)
100 {
101 	udbg_putc = memcons_putc;
102 	udbg_getc = memcons_getc;
103 	udbg_getc_poll = memcons_getc_poll;
104 }
105