1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * A udbg backend which logs messages and reads input from in memory
  4 * buffers.
  5 *
  6 * The console output can be read from memcons_output which is a
  7 * circular buffer whose next write position is stored in memcons.output_pos.
  8 *
  9 * Input may be passed by writing into the memcons_input buffer when it is
 10 * empty. The input buffer is empty when both input_pos == input_start and
 11 * *input_start == '\0'.
 12 *
 13 * Copyright (C) 2003-2005 Anton Blanchard and Milton Miller, IBM Corp
 14 * Copyright (C) 2013 Alistair Popple, IBM Corp
 15 */
 16
 17#include <linux/kernel.h>
 18#include <asm/barrier.h>
 19#include <asm/page.h>
 20#include <asm/processor.h>
 21#include <asm/udbg.h>
 22
 23struct memcons {
 24	char *output_start;
 25	char *output_pos;
 26	char *output_end;
 27	char *input_start;
 28	char *input_pos;
 29	char *input_end;
 30};
 31
 32static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
 33static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
 34
 35struct memcons memcons = {
 36	.output_start = memcons_output,
 37	.output_pos = memcons_output,
 38	.output_end = &memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE],
 39	.input_start = memcons_input,
 40	.input_pos = memcons_input,
 41	.input_end = &memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE],
 42};
 43
 44static void memcons_putc(char c)
 45{
 46	char *new_output_pos;
 47
 48	*memcons.output_pos = c;
 49	wmb();
 50	new_output_pos = memcons.output_pos + 1;
 51	if (new_output_pos >= memcons.output_end)
 52		new_output_pos = memcons.output_start;
 53
 54	memcons.output_pos = new_output_pos;
 55}
 56
 57static int memcons_getc_poll(void)
 58{
 59	char c;
 60	char *new_input_pos;
 61
 62	if (*memcons.input_pos) {
 63		c = *memcons.input_pos;
 64
 65		new_input_pos = memcons.input_pos + 1;
 66		if (new_input_pos >= memcons.input_end)
 67			new_input_pos = memcons.input_start;
 68		else if (*new_input_pos == '\0')
 69			new_input_pos = memcons.input_start;
 70
 71		*memcons.input_pos = '\0';
 72		wmb();
 73		memcons.input_pos = new_input_pos;
 74		return c;
 75	}
 76
 77	return -1;
 78}
 79
 80static int memcons_getc(void)
 81{
 82	int c;
 83
 84	while (1) {
 85		c = memcons_getc_poll();
 86		if (c == -1)
 87			cpu_relax();
 88		else
 89			break;
 90	}
 91
 92	return c;
 93}
 94
 95void __init udbg_init_memcons(void)
 96{
 97	udbg_putc = memcons_putc;
 98	udbg_getc = memcons_getc;
 99	udbg_getc_poll = memcons_getc_poll;
100}