/*
* memconsole.c
*
* Infrastructure for importing the BIOS memory based console
* into the kernel log ringbuffer.
*
* Copyright 2010 Google Inc. All rights reserved.
*/
#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/kobject.h>
#include <linux/module.h>
#include <linux/dmi.h>
#include <asm/bios_ebda.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(struct file *filp, struct kobject *kobp,
struct bin_attribute *bin_attr, char *buf,
loff_t pos, size_t count)
{
return memory_read_from_buffer(buf, count, &pos, memconsole_baseaddr,
memconsole_length);
}
static struct bin_attribute memconsole_bin_attr = {
.attr = {.name = "log", .mode = 0444},
.read = memconsole_read,
};
static void found_v1_header(struct biosmemcon_ebda *hdr)
{
printk(KERN_INFO "BIOS console v1 EBDA structure found at %p\n", hdr);
printk(KERN_INFO "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_length = hdr->v1.num_chars;
memconsole_baseaddr = phys_to_virt(hdr->v1.buffer_addr);
}
static void found_v2_header(struct biosmemcon_ebda *hdr)
{
printk(KERN_INFO "BIOS console v2 EBDA structure found at %p\n", hdr);
printk(KERN_INFO "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_length = hdr->v2.end - hdr->v2.start;
memconsole_baseaddr = phys_to_virt(hdr->v2.buffer_addr
+ hdr->v2.start);
}
/*
* Search through the EBDA for the BIOS Memory Console, and
* set the global variables to point to it. Return true if found.
*/
static bool found_memconsole(void)
{
unsigned int address;
size_t length, cur;
address = get_bios_ebda();
if (!address) {
printk(KERN_INFO "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;
}
}
printk(KERN_INFO "BIOS console EBDA structure not found!\n");
return false;
}
static struct dmi_system_id memconsole_dmi_table[] __initdata = {
{
.ident = "Google Board",
.matches = {
DMI_MATCH(DMI_BOARD_VENDOR, "Google, Inc."),
},
},
{}
};
MODULE_DEVICE_TABLE(dmi, memconsole_dmi_table);
static int __init memconsole_init(void)
{
int ret;
if (!dmi_check_system(memconsole_dmi_table))
return -ENODEV;
if (!found_memconsole())
return -ENODEV;
memconsole_bin_attr.size = memconsole_length;
ret = sysfs_create_bin_file(firmware_kobj, &memconsole_bin_attr);
return ret;
}
static void __exit memconsole_exit(void)
{
sysfs_remove_bin_file(firmware_kobj, &memconsole_bin_attr);
}
module_init(memconsole_init);
module_exit(memconsole_exit);
MODULE_AUTHOR("Google, Inc.");
MODULE_LICENSE("GPL");
