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