1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * memconsole-x86-legacy.c
  4 *
  5 * EBDA specific parts of the memory based BIOS console.
  6 *
  7 * Copyright 2017 Google Inc.
  8 */
  9
 10#include <linux/kernel.h>
 11#include <linux/module.h>
 12#include <linux/dmi.h>
 13#include <linux/mm.h>
 14#include <asm/bios_ebda.h>
 15#include <linux/acpi.h>
 16
 17#include "memconsole.h"
 18
 19#define BIOS_MEMCONSOLE_V1_MAGIC	0xDEADBABE
 20#define BIOS_MEMCONSOLE_V2_MAGIC	(('M')|('C'<<8)|('O'<<16)|('N'<<24))
 21
 22struct biosmemcon_ebda {
 23	u32 signature;
 24	union {
 25		struct {
 26			u8  enabled;
 27			u32 buffer_addr;
 28			u16 start;
 29			u16 end;
 30			u16 num_chars;
 31			u8  wrapped;
 32		} __packed v1;
 33		struct {
 34			u32 buffer_addr;
 35			/* Misdocumented as number of pages! */
 36			u16 num_bytes;
 37			u16 start;
 38			u16 end;
 39		} __packed v2;
 40	};
 41} __packed;
 42
 43static char *memconsole_baseaddr;
 44static size_t memconsole_length;
 45
 46static ssize_t memconsole_read(char *buf, loff_t pos, size_t count)
 47{
 48	return memory_read_from_buffer(buf, count, &pos, memconsole_baseaddr,
 49				       memconsole_length);
 50}
 51
 52static void found_v1_header(struct biosmemcon_ebda *hdr)
 53{
 54	pr_info("memconsole: BIOS console v1 EBDA structure found at %p\n",
 55		hdr);
 56	pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num = %d\n",
 57		hdr->v1.buffer_addr, hdr->v1.start,
 58		hdr->v1.end, hdr->v1.num_chars);
 59
 60	memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr);
 61	memconsole_length = hdr->v1.num_chars;
 62	memconsole_setup(memconsole_read);
 63}
 64
 65static void found_v2_header(struct biosmemcon_ebda *hdr)
 66{
 67	pr_info("memconsole: BIOS console v2 EBDA structure found at %p\n",
 68		hdr);
 69	pr_info("memconsole: BIOS console buffer at 0x%.8x, start = %d, end = %d, num_bytes = %d\n",
 70		hdr->v2.buffer_addr, hdr->v2.start,
 71		hdr->v2.end, hdr->v2.num_bytes);
 72
 73	memconsole_baseaddr = phys_to_virt(hdr->v2.buffer_addr + hdr->v2.start);
 74	memconsole_length = hdr->v2.end - hdr->v2.start;
 75	memconsole_setup(memconsole_read);
 76}
 77
 78/*
 79 * Search through the EBDA for the BIOS Memory Console, and
 80 * set the global variables to point to it.  Return true if found.
 81 */
 82static bool memconsole_ebda_init(void)
 83{
 84	unsigned int address;
 85	size_t length, cur;
 86
 87	address = get_bios_ebda();
 88	if (!address) {
 89		pr_info("memconsole: BIOS EBDA non-existent.\n");
 90		return false;
 91	}
 92
 93	/* EBDA length is byte 0 of EBDA (in KB) */
 94	length = *(u8 *)phys_to_virt(address);
 95	length <<= 10; /* convert to bytes */
 96
 97	/*
 98	 * Search through EBDA for BIOS memory console structure
 99	 * note: signature is not necessarily dword-aligned
100	 */
101	for (cur = 0; cur < length; cur++) {
102		struct biosmemcon_ebda *hdr = phys_to_virt(address + cur);
103
104		/* memconsole v1 */
105		if (hdr->signature == BIOS_MEMCONSOLE_V1_MAGIC) {
106			found_v1_header(hdr);
107			return true;
108		}
109
110		/* memconsole v2 */
111		if (hdr->signature == BIOS_MEMCONSOLE_V2_MAGIC) {
112			found_v2_header(hdr);
113			return true;
114		}
115	}
116
117	pr_info("memconsole: BIOS console EBDA structure not found!\n");
118	return false;
119}
120
121static const struct dmi_system_id memconsole_dmi_table[] __initconst = {
122	{
123		.ident = "Google Board",
124		.matches = {
125			DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."),
126		},
127	},
128	{}
129};
130MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table);
131
132static bool __init memconsole_find(void)
133{
134	if (!dmi_check_system(memconsole_dmi_table))
135		return false;
136
137	return memconsole_ebda_init();
138}
139
140static int __init memconsole_x86_init(void)
141{
142	if (!memconsole_find())
143		return -ENODEV;
144
145	return memconsole_sysfs_init();
146}
147
148static void __exit memconsole_x86_exit(void)
149{
150	memconsole_exit();
151}
152
153module_init(memconsole_x86_init);
154module_exit(memconsole_x86_exit);
155
156MODULE_AUTHOR("Google, Inc.");
157MODULE_LICENSE("GPL");