158 lines
3.5 KiB
C
158 lines
3.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* memconsole-x86-legacy.c
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*
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* EBDA specific parts of the memory based BIOS console.
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*
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* Copyright 2017 Google Inc.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/dmi.h>
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#include <linux/mm.h>
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#include <asm/bios_ebda.h>
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#include <linux/acpi.h>
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#include "memconsole.h"
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#define BIOS_MEMCONSOLE_V1_MAGIC 0xDEADBABE
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#define BIOS_MEMCONSOLE_V2_MAGIC (('M')|('C'<<8)|('O'<<16)|('N'<<24))
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struct biosmemcon_ebda {
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u32 signature;
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union {
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struct {
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u8 enabled;
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u32 buffer_addr;
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u16 start;
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u16 end;
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u16 num_chars;
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u8 wrapped;
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} __packed v1;
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struct {
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u32 buffer_addr;
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/* Misdocumented as number of pages! */
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u16 num_bytes;
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u16 start;
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u16 end;
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} __packed v2;
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};
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} __packed;
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static char *memconsole_baseaddr;
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static size_t memconsole_length;
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static ssize_t memconsole_read(char *buf, loff_t pos, size_t count)
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{
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return memory_read_from_buffer(buf, count, &pos, memconsole_baseaddr,
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memconsole_length);
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}
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static void found_v1_header(struct biosmemcon_ebda *hdr)
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{
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pr_info("memconsole: BIOS console v1 EBDA structure found at %p\n",
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hdr);
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pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num = %d\n",
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hdr->v1.buffer_addr, hdr->v1.start,
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hdr->v1.end, hdr->v1.num_chars);
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memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr);
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memconsole_length = hdr->v1.num_chars;
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memconsole_setup(memconsole_read);
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}
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static void found_v2_header(struct biosmemcon_ebda *hdr)
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{
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pr_info("memconsole: BIOS console v2 EBDA structure found at %p\n",
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hdr);
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pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num_bytes = %d\n",
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hdr->v2.buffer_addr, hdr->v2.start,
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hdr->v2.end, hdr->v2.num_bytes);
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memconsole_baseaddr = phys_to_virt(hdr->v2.buffer_addr + hdr->v2.start);
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memconsole_length = hdr->v2.end - hdr->v2.start;
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memconsole_setup(memconsole_read);
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}
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/*
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* Search through the EBDA for the BIOS Memory Console, and
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* set the global variables to point to it. Return true if found.
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*/
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static bool memconsole_ebda_init(void)
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{
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unsigned int address;
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size_t length, cur;
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address = get_bios_ebda();
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if (!address) {
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pr_info("memconsole: BIOS EBDA non-existent.\n");
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return false;
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}
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/* EBDA length is byte 0 of EBDA (in KB) */
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length = *(u8 *)phys_to_virt(address);
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length <<= 10; /* convert to bytes */
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/*
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* Search through EBDA for BIOS memory console structure
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* note: signature is not necessarily dword-aligned
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*/
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for (cur = 0; cur < length; cur++) {
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struct biosmemcon_ebda *hdr = phys_to_virt(address + cur);
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/* memconsole v1 */
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if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) {
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found_v1_header(hdr);
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return true;
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}
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/* memconsole v2 */
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if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) {
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found_v2_header(hdr);
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return true;
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}
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}
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pr_info("memconsole: BIOS console EBDA structure not found!\n");
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return false;
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}
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static const struct dmi_system_id memconsole_dmi_table[] __initconst = {
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{
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.ident = "Google Board",
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.matches = {
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DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."),
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},
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},
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{}
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};
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MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table);
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static bool __init memconsole_find(void)
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{
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if (!dmi_check_system(memconsole_dmi_table))
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return false;
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return memconsole_ebda_init();
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}
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static int __init memconsole_x86_init(void)
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{
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if (!memconsole_find())
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return -ENODEV;
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return memconsole_sysfs_init();
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}
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static void __exit memconsole_x86_exit(void)
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{
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memconsole_exit();
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}
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module_init(memconsole_x86_init);
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module_exit(memconsole_x86_exit);
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MODULE_AUTHOR("Google, Inc.");
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MODULE_LICENSE("GPL");
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