arch/powerpc/sysdev/udbg_memcons.c

   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
  23 struct 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
  32 static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
  33 static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
  34
  35 struct 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
  44 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
  57 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
  80 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
  95 void udbg_init_memcons(void)
  96 {
  97         udbg_putc = memcons_putc;
  98         udbg_getc = memcons_getc;
  99         udbg_getc_poll = memcons_getc_poll;
 100 }