linux/arch/powerpc/sysdev/udbg_memcons.c
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   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
  44void 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
  57int 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
  80int 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 udbg_init_memcons(void)
  96{
  97        udbg_putc = memcons_putc;
  98        udbg_getc = memcons_getc;
  99        udbg_getc_poll = memcons_getc_poll;
 100}
 101