arch/powerpc/sysdev/udbg_memcons.c

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