LXR linux/arch/powerpc/sysdev/udbg

   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
  28struct 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
  37static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
  38static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
  39
  40struct 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
  49void 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
  62int 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
  85int 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
 100void udbg_init_memcons(void)
 101{
 102        udbg_putc = memcons_putc;
 103        udbg_getc = memcons_getc;
 104        udbg_getc_poll = memcons_getc_poll;
 105}
 106