powerpc/sysdev/udbg_memcons.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * A udbg backend which logs messages and reads input from in memory
0004  * buffers.
0005  *
0006  * The console output can be read from memcons_output which is a
0007  * circular buffer whose next write position is stored in memcons.output_pos.
0008  *
0009  * Input may be passed by writing into the memcons_input buffer when it is
0010  * empty. The input buffer is empty when both input_pos == input_start and
0011  * *input_start == '\0'.
0012  *
0013  * Copyright (C) 2003-2005 Anton Blanchard and Milton Miller, IBM Corp
0014  * Copyright (C) 2013 Alistair Popple, IBM Corp
0015  */
0016
0017 #include <linux/kernel.h>
0018 #include <asm/barrier.h>
0019 #include <asm/page.h>
0020 #include <asm/processor.h>
0021 #include <asm/udbg.h>
0022
0023 struct memcons {
0024     char *output_start;
0025     char *output_pos;
0026     char *output_end;
0027     char *input_start;
0028     char *input_pos;
0029     char *input_end;
0030 };
0031
0032 static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
0033 static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
0034
0035 struct memcons memcons = {
0036     .output_start = memcons_output,
0037     .output_pos = memcons_output,
0038     .output_end = &memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE],
0039     .input_start = memcons_input,
0040     .input_pos = memcons_input,
0041     .input_end = &memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE],
0042 };
0043
0044 void memcons_putc(char c)
0045 {
0046     char *new_output_pos;
0047
0048     *memcons.output_pos = c;
0049     wmb();
0050     new_output_pos = memcons.output_pos + 1;
0051     if (new_output_pos >= memcons.output_end)
0052         new_output_pos = memcons.output_start;
0053
0054     memcons.output_pos = new_output_pos;
0055 }
0056
0057 int memcons_getc_poll(void)
0058 {
0059     char c;
0060     char *new_input_pos;
0061
0062     if (*memcons.input_pos) {
0063         c = *memcons.input_pos;
0064
0065         new_input_pos = memcons.input_pos + 1;
0066         if (new_input_pos >= memcons.input_end)
0067             new_input_pos = memcons.input_start;
0068         else if (*new_input_pos == '\0')
0069             new_input_pos = memcons.input_start;
0070
0071         *memcons.input_pos = '\0';
0072         wmb();
0073         memcons.input_pos = new_input_pos;
0074         return c;
0075     }
0076
0077     return -1;
0078 }
0079
0080 int memcons_getc(void)
0081 {
0082     int c;
0083
0084     while (1) {
0085         c = memcons_getc_poll();
0086         if (c == -1)
0087             cpu_relax();
0088         else
0089             break;
0090     }
0091
0092     return c;
0093 }
0094
0095 void __init udbg_init_memcons(void)
0096 {
0097     udbg_putc = memcons_putc;
0098     udbg_getc = memcons_getc;
0099     udbg_getc_poll = memcons_getc_poll;
0100 }