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 static 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 static 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 static 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 __init udbg_init_memcons(void) 96 { 97 udbg_putc = memcons_putc; 98 udbg_getc = memcons_getc; 99 udbg_getc_poll = memcons_getc_poll; 100 } 101