30650239ad
This patch adds a new udbg early debug console which utilises statically defined input and output buffers stored within the kernel BSS. It is primarily designed to assist with bring up of new hardware which may not have a working console but which has a method of reading/writing kernel memory. This version incorporates comments made by Ben H (thanks!). Changes from v1: - Add memory barriers. - Ensure updating of read/write positions is atomic. Signed-off-by: Alistair Popple <alistair@popple.id.au> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
106 lines
2.4 KiB
C
106 lines
2.4 KiB
C
/*
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* A udbg backend which logs messages and reads input from in memory
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* buffers.
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*
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* The console output can be read from memcons_output which is a
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* circular buffer whose next write position is stored in memcons.output_pos.
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*
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* Input may be passed by writing into the memcons_input buffer when it is
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* empty. The input buffer is empty when both input_pos == input_start and
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* *input_start == '\0'.
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*
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* Copyright (C) 2003-2005 Anton Blanchard and Milton Miller, IBM Corp
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* Copyright (C) 2013 Alistair Popple, IBM Corp
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <asm/barrier.h>
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#include <asm/page.h>
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#include <asm/processor.h>
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#include <asm/udbg.h>
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struct memcons {
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char *output_start;
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char *output_pos;
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char *output_end;
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char *input_start;
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char *input_pos;
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char *input_end;
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};
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static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
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static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
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struct memcons memcons = {
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.output_start = memcons_output,
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.output_pos = memcons_output,
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.output_end = &memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE],
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.input_start = memcons_input,
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.input_pos = memcons_input,
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.input_end = &memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE],
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};
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void memcons_putc(char c)
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{
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char *new_output_pos;
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*memcons.output_pos = c;
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wmb();
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new_output_pos = memcons.output_pos + 1;
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if (new_output_pos >= memcons.output_end)
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new_output_pos = memcons.output_start;
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memcons.output_pos = new_output_pos;
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}
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int memcons_getc_poll(void)
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{
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char c;
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char *new_input_pos;
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if (*memcons.input_pos) {
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c = *memcons.input_pos;
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new_input_pos = memcons.input_pos + 1;
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if (new_input_pos >= memcons.input_end)
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new_input_pos = memcons.input_start;
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else if (*new_input_pos == '\0')
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new_input_pos = memcons.input_start;
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*memcons.input_pos = '\0';
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wmb();
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memcons.input_pos = new_input_pos;
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return c;
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}
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return -1;
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}
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int memcons_getc(void)
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{
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int c;
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while (1) {
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c = memcons_getc_poll();
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if (c == -1)
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cpu_relax();
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else
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break;
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}
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return c;
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}
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void udbg_init_memcons(void)
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{
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udbg_putc = memcons_putc;
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udbg_getc = memcons_getc;
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udbg_getc_poll = memcons_getc_poll;
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}
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