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
27struct 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
36static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
37static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
38
39struct 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
48void 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
61int 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
84int 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
99void udbg_init_memcons(void)
100{
101	udbg_putc = memcons_putc;
102	udbg_getc = memcons_getc;
103	udbg_getc_poll = memcons_getc_poll;
104}
105