ELOG: Add support for flash based event log

This is based around the SMBIOS event log specification but
expanded with OEM event types to support more specific and
relevant system events.

It requires flash storage and a minimum 4K block (or flash block
size) that should be allocated in the FMAP.

A copy of the event log is maintained in memory for convenience
and speed and the in-memory copy is written to flash at specific
points.

The log is automatically shunk when it reaches a configurable
full threshold in order to not get stuck with a full log that
needs OS help to clear.

ELOG implements the specification published here:
http://code.google.com/p/firmware-event-log/wiki/FirmwareEventLogDesign

And is similar to what we use in other firmware at Google.
This implementation does not support double-buffered flash
regions.  This is done because speed is valued over the log
reliability and it keeps the code simpler for the first version.

This is a large commit and by itself it just provides a new
driver that is made available to coreboot.  Without additional
patches it is not very useful, but the end result is an event
log that will contain entries like this:

171 | 2012-06-23 16:02:55 | System boot | 285
172 | 2012-06-23 16:02:55 | EC Event | Power Button
173 | 2012-06-23 16:02:55 | SUS Power Fail
174 | 2012-06-23 16:02:55 | System Reset
175 | 2012-06-23 16:02:55 | ACPI Wake | S5

Change-Id: I985524c67f525c8a268eccbd856c1a4c2a426889
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/1311
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

4 files changed, 1026 insertions, 0 deletions

diff --git a/src/drivers/elog/Kconfig b/src/drivers/elog/Kconfig
new file mode 100644
index 0000000000..d61dd10857
--- /dev/null
+++ b/src/drivers/elog/Kconfig
@@ -0,0 +1,69 @@
+##
+## This file is part of the coreboot project.
+##
+## Copyright (C) 2012 The Chromium OS Authors.  All rights reserved.
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; version 2 of the License.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, write to the Free Software
+## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+##
+
+config ELOG
+	depends on SPI_FLASH
+	bool "Support for flash based event log"
+	default n
+	help
+	  Enable support for flash based event logging.
+
+if ELOG
+
+config ELOG_DEBUG
+	bool "Enable debug output for event logging"
+	default n
+
+config ELOG_FLASH_BASE
+	hex "Event log offset into flash"
+	default 0
+	help
+	  Offset into the flash chip for the ELOG block.
+	  This should be allocated in the FMAP.
+
+config ELOG_AREA_SIZE
+	hex "Size of Event Log area in flash"
+	default 0x1000
+	help
+	  This should be a multiple of flash block size.
+
+	  Default is 4K.
+
+config ELOG_FULL_THRESHOLD
+	hex "Threshold at which flash is considered full"
+	default 0xC00
+	help
+	  When the Event Log size is larger than this it will be shrunk
+	  to ELOG_SHRINK_SIZE.  Must be greater than ELOG_AREA_SIZE, and
+	  ELOG_AREA_SIZE - ELOG_FULL_THRESHOLD must be greater than the
+	  maximum event size of 128.
+
+	  Default is 75% of the log, or 3K.
+
+config ELOG_SHRINK_SIZE
+	hex "Resulting size when the event log is shrunk"
+	default 0x400
+	help
+	  When the Event Log is shrunk it will go to this size.
+	  ELOG_AREA_SIZE - ELOG_SHRINK_SIZE must be less than
+	  CONFIG_ELOG_FULL_THRESHOLD.
+
+	  Default is 1K.
+
+endif
diff --git a/src/drivers/elog/Makefile.inc b/src/drivers/elog/Makefile.inc
new file mode 100644
index 0000000000..a01841db96
--- /dev/null
+++ b/src/drivers/elog/Makefile.inc
@@ -0,0 +1 @@
+ramstage-$(CONFIG_ELOG) += elog.c
diff --git a/src/drivers/elog/elog.c b/src/drivers/elog/elog.c
new file mode 100644
index 0000000000..8e56b85242
--- /dev/null
+++ b/src/drivers/elog/elog.c
@@ -0,0 +1,880 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2012 The ChromiumOS Authors.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA, 02110-1301 USA
+ */
+
+#include <arch/acpi.h>
+#include <console/console.h>
+#include <pc80/mc146818rtc.h>
+#include <spi.h>
+#include <spi_flash.h>
+#include <stdint.h>
+#include <string.h>
+#include <elog.h>
+#include "elog_internal.h"
+
+#if CONFIG_ELOG_FLASH_BASE == 0
+#error "CONFIG_ELOG_FLASH_BASE is invalid"
+#endif
+#if CONFIG_ELOG_FULL_THRESHOLD >= CONFIG_ELOG_AREA_SIZE
+#error "CONFIG_ELOG_FULL_THRESHOLD is larger than CONFIG_ELOG_AREA_SIZE"
+#endif
+#if (CONFIG_ELOG_AREA_SIZE - CONFIG_ELOG_FULL_THRESHOLD) < (MAX_EVENT_SIZE + 1)
+#error "CONFIG_ELOG_FULL_THRESHOLD is too small"
+#endif
+#if CONFIG_ELOG_SHRINK_SIZE >= CONFIG_ELOG_AREA_SIZE
+#error "CONFIG_ELOG_SHRINK_SIZE is larger than CONFIG_ELOG_AREA_SIZE"
+#endif
+#if (CONFIG_ELOG_AREA_SIZE - CONFIG_ELOG_SHRINK_SIZE) > \
+	CONFIG_ELOG_FULL_THRESHOLD
+#error "CONFIG_ELOG_SHRINK_SIZE is too large"
+#endif
+
+#if CONFIG_ELOG_DEBUG
+#define elog_debug(STR...) printk(BIOS_DEBUG, STR)
+#else
+#define elog_debug(STR...)
+#endif
+
+/*
+ * Static variables for ELOG state
+ */
+static int elog_initialized;
+static struct spi_flash *elog_spi;
+static struct elog_descriptor elog_flash_area;
+static struct elog_descriptor elog_mem_area;
+
+static inline struct elog_descriptor* elog_get_mem(void)
+{
+	return &elog_mem_area;
+}
+
+static inline struct elog_descriptor* elog_get_flash(void)
+{
+	return &elog_flash_area;
+}
+
+/*
+ * Convert a memory mapped flash address into a flash offset
+ */
+static inline u32 elog_flash_address_to_offset(u8 *address)
+{
+	if (!elog_spi)
+		return 0;
+	return (u32)address - ((u32)~0UL - elog_spi->size + 1);
+}
+
+/*
+ * Convert a flash offset into a memory mapped flash address
+ */
+static inline u8* elog_flash_offset_to_address(u32 offset)
+{
+	if (!elog_spi)
+		return NULL;
+	return (u8*)((u32)~0UL - elog_spi->size + 1 + offset);
+}
+
+/*
+ * The ELOG header is at the very beginning of the area
+ */
+static inline struct elog_header*
+elog_get_header(struct elog_descriptor *elog)
+{
+	return elog->backing_store;
+}
+
+/*
+ * Pointer to an event log header in the event data area
+ */
+static inline struct event_header*
+elog_get_event_base(struct elog_descriptor *elog, u32 offset)
+{
+	return (struct event_header *)&elog->data[offset];
+}
+
+/*
+ * Pointer to where the next event should be stored
+ */
+static inline struct event_header*
+elog_get_next_event_base(struct elog_descriptor *elog)
+{
+	return elog_get_event_base(elog, elog->next_event_offset);
+}
+
+/*
+ * Pointer to the last logged event
+ */
+static inline struct event_header*
+elog_get_last_event_base(struct elog_descriptor *elog)
+{
+	return elog_get_event_base(elog, elog->last_event_offset);
+}
+
+/*
+ * Update the checksum at the last byte
+ */
+static void elog_update_checksum(struct event_header *event, u8 checksum)
+{
+	u8 *event_data = (u8*)event;
+	event_data[event->length - 1] = checksum;
+}
+
+/*
+ * Simple byte checksum for events
+ */
+static u8 elog_checksum_event(struct event_header *event)
+{
+	u8 index, checksum = 0;
+	u8 *data = (u8*)event;
+
+	for (index = 0; index < event->length; index++)
+		checksum += data[index];
+	return checksum;
+}
+
+/*
+ * Check if a raw buffer is filled with ELOG_TYPE_EOL byte
+ */
+static int elog_is_buffer_clear(u8 *base, u32 size)
+{
+	u8 *current = base;
+	u8 *end = current + size;
+
+	elog_debug("elog_is_buffer_clear(base=0x%p size=%u)\n", base, size);
+
+	for (; current != end; current++) {
+		if (*current != ELOG_TYPE_EOL)
+			return 0;
+	}
+	return 1;
+}
+
+/*
+ * Verify whether ELOG area is filled with ELOG_TYPE_EOL byte
+ */
+static int elog_is_area_clear(struct elog_descriptor *elog)
+{
+	return elog_is_buffer_clear(elog->backing_store, elog->total_size);
+}
+
+/*
+ * Check that the ELOG area has been initialized and is valid.
+ */
+static int elog_is_area_valid(struct elog_descriptor *elog)
+{
+	elog_debug("elog_is_area_valid()\n");
+
+	if (elog->area_state != ELOG_AREA_HAS_CONTENT)
+		return 0;
+	if (elog->header_state != ELOG_HEADER_VALID)
+		return 0;
+	if (elog->event_buffer_state != ELOG_EVENT_BUFFER_OK)
+		return 0;
+	return 1;
+}
+
+/*
+ * Verify the contents of an ELOG Header structure
+ * Returns 1 if the header is valid, 0 otherwise
+ */
+static int elog_is_header_valid(struct elog_header *header)
+{
+	elog_debug("elog_is_header_valid()\n");
+
+	if (header->magic != ELOG_SIGNATURE) {
+		printk(BIOS_ERR, "ELOG: header magic 0x%X != 0x%X\n",
+		       header->magic, ELOG_SIGNATURE);
+		return 0;
+	}
+	if (header->version != ELOG_VERSION) {
+		printk(BIOS_ERR, "ELOG: header version %u != %u\n",
+		       header->version, ELOG_VERSION);
+		return 0;
+	}
+	if (header->header_size != sizeof(*header)) {
+		printk(BIOS_ERR, "ELOG: header size mismatch %u != %u\n",
+		       header->header_size, sizeof(*header));
+		return 0;
+	}
+	return 1;
+}
+
+/*
+ * Validate the event header and data.
+ */
+static int elog_is_event_valid(struct elog_descriptor *elog, u32 offset)
+{
+	struct event_header *event;
+
+	event = elog_get_event_base(elog, offset);
+	if (!event)
+		return 0;
+
+	/* Validate event length */
+	if ((offsetof(struct event_header, type) +
+	     sizeof(event->type) - 1 + offset) >= elog->data_size)
+		return 0;
+
+	/* End of event marker has been found */
+	if (event->type == ELOG_TYPE_EOL)
+		return 0;
+
+	/* Check if event fits in area */
+	if ((offsetof(struct event_header, length) +
+	     sizeof(event->length) - 1 + offset) >= elog->data_size)
+		return 0;
+
+	/*
+	 * If the current event length + the current offset exceeds
+	 * the area size then the event area is corrupt.
+	 */
+	if ((event->length + offset) >= elog->data_size)
+		return 0;
+
+	/* Event length must be at least header size + checksum */
+	if (event->length < (sizeof(*event) + 1))
+		return 0;
+
+	/* If event checksum is invalid the area is corrupt */
+	if (elog_checksum_event(event) != 0)
+		return 0;
+
+	/* Event is valid */
+	return 1;
+}
+
+/*
+ * Write 'size' bytes of data provided in 'buffer' into flash
+ * device at offset 'offset'. This will not erase the flash and
+ * it assumes the flash area is erased appropriately.
+ */
+static void elog_flash_write(u8 *address, u8 *buffer, u32 size)
+{
+	u32 offset;
+
+	if (!address || !buffer || !size || !elog_spi)
+		return;
+
+	offset = elog_flash_address_to_offset(address);
+
+	elog_debug("elog_flash_write(address=0x%p offset=0x%08x buffer=0x%p "
+		   "size=%u)\n", address, offset, buffer, size);
+
+	/* Write the data to flash */
+	elog_spi->write(elog_spi, offset, size, buffer);
+}
+
+/*
+ * Erase the first block specified in the address.
+ * Only handles flash area within a single flash block.
+ */
+static void elog_flash_erase(u8 *address, u32 size)
+{
+	u32 offset;
+
+	if (!address || !size || !elog_spi)
+		return;
+
+	offset = elog_flash_address_to_offset(address);
+
+	elog_debug("elog_flash_erase(address=0x%p offset=0x%08x size=%u)\n",
+		   address, offset, size);
+
+	/* Erase the sectors in this region */
+	elog_spi->erase(elog_spi, offset, size);
+}
+
+/*
+ * Scan the event area and validate each entry and
+ * update the ELOG descriptor state.
+ */
+static void elog_update_event_buffer_state(struct elog_descriptor *elog)
+{
+	u32 count = 0;
+	u32 offset = 0;
+	u32 last_offset = 0;
+	u32 last_event_size = 0;
+	struct event_header *event;
+
+	elog_debug("elog_update_event_buffer_state()\n");
+
+	/* Go through each event and validate it */
+	while (1) {
+		event = elog_get_event_base(elog, offset);
+
+		/* Do not de-reference anything past the area length */
+		if ((offsetof(struct event_header, type) +
+		     sizeof(event->type) - 1 + offset) >= elog->data_size) {
+			elog->event_buffer_state = ELOG_EVENT_BUFFER_CORRUPTED;
+			break;
+		}
+
+		/* The end of the event marker has been found */
+		if (event->type == ELOG_TYPE_EOL)
+			break;
+
+		/* Validate the event */
+		if (!elog_is_event_valid(elog, offset)) {
+			elog->event_buffer_state = ELOG_EVENT_BUFFER_CORRUPTED;
+			break;
+		}
+
+		/* Move to the next event */
+		count++;
+		last_offset = offset;
+		last_event_size = event->length;
+		offset += event->length;
+	}
+
+	/* Ensure the remaining buffer is empty */
+	if (!elog_is_buffer_clear(&elog->data[offset],
+				  elog->data_size - offset))
+		elog->event_buffer_state = ELOG_EVENT_BUFFER_CORRUPTED;
+
+	/* Update data into elog descriptor */
+	elog->event_count = count;
+	elog->next_event_offset = offset;
+	elog->last_event_offset = last_offset;
+	elog->last_event_size = last_event_size;
+}
+
+static void elog_validate_and_fill(struct elog_descriptor *elog)
+{
+	elog_debug("elog_validate_and_fill()\n");
+
+	/* Check if the area is empty or not */
+	if (elog_is_area_clear(elog)) {
+		elog->area_state = ELOG_AREA_EMPTY;
+		return;
+	}
+
+	elog->area_state = ELOG_AREA_HAS_CONTENT;
+
+	/* Validate the header */
+	if (!elog_is_header_valid(elog->staging_header)) {
+		elog->header_state = ELOG_HEADER_INVALID;
+		return;
+	}
+
+	elog->header_state = ELOG_HEADER_VALID;
+	elog_update_event_buffer_state(elog);
+}
+
+/*
+ * Initialize a new ELOG descriptor
+ */
+static void elog_init_descriptor(struct elog_descriptor *elog,
+				 elog_descriptor_type type,
+				 u8 *buffer, u32 size,
+				 struct elog_header *header)
+{
+	elog_debug("elog_init_descriptor(type=%u buffer=0x%p size=%u)\n",
+		   type, buffer, size);
+
+	elog->type = type;
+	elog->area_state = ELOG_AREA_UNDEFINED;
+	elog->header_state = ELOG_HEADER_INVALID;
+	elog->event_buffer_state = ELOG_EVENT_BUFFER_OK;
+	elog->backing_store = buffer;
+	elog->total_size = size;
+
+	/* Get staging header from backing store */
+	elog->staging_header = header;
+	memcpy(header, buffer, sizeof(struct elog_header));
+
+	/* Data starts immediately after header */
+	elog->data = &buffer[sizeof(struct elog_header)];
+	elog->data_size = size - sizeof(struct elog_header);
+
+	elog->next_event_offset = 0;
+	elog->last_event_offset = 0;
+	elog->last_event_size = 0;
+	elog->event_count = 0;
+
+	elog_validate_and_fill(elog);
+}
+
+/*
+ * Re-initialize an existing ELOG descriptor
+ */
+static void elog_reinit_descriptor(struct elog_descriptor *elog)
+{
+	elog_debug("elog_reinit_descriptor()\n");
+	elog_init_descriptor(elog, elog->type, elog->backing_store,
+			     elog->total_size, elog->staging_header);
+}
+
+/*
+ * Create ELOG descriptor data structures for all ELOG areas.
+ */
+static int elog_setup_descriptors(u32 flash_base, u32 area_size)
+{
+	struct elog_header *staging_header;
+	u8 *area;
+
+	elog_debug("elog_setup_descriptors(base=0x%08x size=%u)\n",
+		   flash_base, area_size);
+
+	/* Prepare flash descriptors */
+	if (flash_base == 0) {
+		printk(BIOS_ERR, "ELOG: Invalid flash base\n");
+		return -1;
+	}
+
+	staging_header = malloc(sizeof(struct elog_header));
+	if (!staging_header) {
+		printk(BIOS_ERR, "ELOG: Unable to allocate header\n");
+		return -1;
+	}
+
+	area = elog_flash_offset_to_address(flash_base);
+	if (!area) {
+		printk(BIOS_ERR, "ELOG: Unable to determine flash address\n");
+		return -1;
+	}
+	elog_init_descriptor(elog_get_flash(), ELOG_DESCRIPTOR_FLASH,
+			     area, area_size, staging_header);
+
+	/* Initialize the memory area to look like a cleared flash area */
+	area = malloc(area_size);
+	if (!area) {
+		printk(BIOS_ERR, "ELOG: Unable to allocate mem area\n");
+		return -1;
+	}
+	memset(area, ELOG_TYPE_EOL, area_size);
+	elog_init_descriptor(elog_get_mem(), ELOG_DESCRIPTOR_MEMORY,
+			     area, area_size, (struct elog_header *)area);
+
+	return 0;
+}
+
+static void elog_flash_erase_area(void)
+{
+	struct elog_descriptor *elog = elog_get_flash();
+
+	elog_debug("elog_flash_erase_area()\n");
+
+	elog_flash_erase(elog->backing_store, elog->total_size);
+	elog_reinit_descriptor(elog);
+}
+
+static void elog_prepare_empty(struct elog_descriptor *elog,
+			       u8 *data, u32 data_size)
+{
+	struct elog_header *header;
+
+	elog_debug("elog_prepare_empty(%u bytes)\n", data_size);
+
+	if (!elog_is_area_clear(elog))
+		return;
+
+	/* Write out the header */
+	header = elog->staging_header;
+	header->magic = ELOG_SIGNATURE;
+	header->version = ELOG_VERSION;
+	header->header_size = sizeof(struct elog_header);
+	header->reserved[0] = ELOG_TYPE_EOL;
+	header->reserved[1] = ELOG_TYPE_EOL;
+	elog_flash_write(elog->backing_store, (u8*)header,
+			 header->header_size);
+
+	/* Write out the data */
+	if (data)
+		elog_flash_write(elog->data, data, data_size);
+
+	elog_reinit_descriptor(elog);
+
+	/* Clear the log if corrupt */
+	if (!elog_is_area_valid(elog))
+		elog_flash_erase_area();
+}
+
+static int elog_sync_flash_to_mem(void)
+{
+	struct elog_descriptor *mem = elog_get_mem();
+	struct elog_descriptor *flash = elog_get_flash();
+
+	elog_debug("elog_sync_flash_to_mem()\n");
+
+	/* Fill with empty pattern first */
+	memset(mem->backing_store, ELOG_TYPE_EOL, mem->total_size);
+
+	/* Copy the header to memory */
+	memcpy(mem->backing_store, flash->backing_store,
+	       sizeof(struct elog_header));
+
+	/* Copy the valid flash contents to memory */
+	memcpy(mem->data, flash->data, flash->next_event_offset);
+
+	elog_reinit_descriptor(mem);
+
+	return elog_is_area_valid(mem) ? 0 : -1;
+}
+
+static int elog_sync_mem_to_flash(void)
+{
+	struct elog_descriptor *mem = elog_get_mem();
+	struct elog_descriptor *flash = elog_get_flash();
+	u8 *src, *dest;
+	u32 size;
+
+	elog_debug("elog_sync_mem_to_flash()\n");
+
+	/*
+	 * In the case of a BIOS flash the active area will be cleared.
+	 * One can catch this case and log the proper shutdown event by
+	 * checking if the active flash elog is empty.  Note that if the
+	 * header size changes we will have corrupted the flash area.
+	 * However that will be corrected on the next boot.
+	 */
+	if (elog_is_area_clear(flash)) {
+		elog_prepare_empty(flash,
+				   (u8*)elog_get_last_event_base(mem),
+				   mem->last_event_size);
+		elog_sync_flash_to_mem();
+		return 0;
+	}
+
+	/* Calculate the destination and source bases */
+	dest = (u8*)elog_get_next_event_base(flash);
+	src = (u8*)elog_get_event_base(mem, flash->next_event_offset);
+
+	/* Calculate how much data to sync */
+	size = mem->next_event_offset - flash->next_event_offset;
+
+	/* Write the log data */
+	elog_flash_write(dest, src, size);
+
+	/* Update descriptor */
+	flash->event_count = mem->event_count;
+	flash->next_event_offset = mem->next_event_offset;
+	flash->last_event_offset = mem->last_event_offset;
+	flash->last_event_size = mem->last_event_size;
+
+	return 0;
+}
+
+/*
+ * Called during ELOG entry handler to prepare state for flash.
+ */
+static int elog_flash_area_bootstrap(void)
+{
+	struct elog_descriptor *elog = elog_get_flash();
+
+	elog_debug("elog_flash_area_bootstrap()\n");
+
+	switch (elog->area_state) {
+	case ELOG_AREA_UNDEFINED:
+		printk(BIOS_ERR, "ELOG: flash area undefined\n");
+		return -1;
+
+	case ELOG_AREA_EMPTY:
+		/* Write a new header with no data */
+		elog_prepare_empty(elog, NULL, 0);
+		break;
+
+	case ELOG_AREA_HAS_CONTENT:
+		break;
+	}
+
+	if (elog->header_state == ELOG_HEADER_INVALID) {
+		/* If the header is invalid no events can be salvaged
+		 * so erase the entire area. */
+		printk(BIOS_ERR, "ELOG: flash area header invalid\n");
+		elog_flash_erase_area();
+		elog_prepare_empty(elog, NULL, 0);
+	}
+
+	if (elog->event_buffer_state == ELOG_EVENT_BUFFER_CORRUPTED) {
+		/* Wipe the source flash area */
+		elog_flash_erase_area();
+		elog_prepare_empty(elog, elog_get_mem()->data,
+				   elog_get_mem()->next_event_offset);
+	}
+
+	return 0;
+}
+
+/*
+ * Shrink the log, deleting old entries and moving the
+ * remining ones to the front of the log.
+ */
+static int elog_shrink(void)
+{
+	struct elog_descriptor *mem = elog_get_mem();
+	struct event_header *event;
+	u16 discard_count = 0;
+	u16 offset = 0;
+
+	elog_debug("elog_shrink()\n");
+
+	if (mem->next_event_offset < CONFIG_ELOG_SHRINK_SIZE)
+		return 0;
+
+	while (1) {
+		/* Next event has exceeded constraints */
+		if (offset > CONFIG_ELOG_SHRINK_SIZE)
+			break;
+
+		event = elog_get_event_base(mem, offset);
+
+		/* Reached the end of the area */
+		if (!event || event->type == ELOG_TYPE_EOL)
+			break;
+
+		offset += event->length;
+		discard_count++;
+	}
+
+	/* Erase flash area */
+	elog_flash_erase_area();
+
+	/* Write new flash area */
+	elog_prepare_empty(elog_get_flash(),
+			   (u8*)elog_get_event_base(mem, offset),
+			   mem->next_event_offset - offset);
+
+	/* Update memory area from flash */
+	if (elog_sync_flash_to_mem() < 0) {
+		printk(BIOS_ERR, "Unable to update memory area from flash\n");
+		return -1;
+	}
+
+	/* Add clear event */
+	elog_add_event_word(ELOG_TYPE_LOG_CLEAR, offset);
+
+	return 0;
+}
+
+/*
+ * Initialize the SPI bus and probe for a flash chip
+ */
+static int elog_spi_init(void)
+{
+	elog_debug("elog_spi_init()\n");
+
+	/* Prepare SPI subsystem */
+	spi_init();
+
+	/* Look for flash chip */
+	elog_spi = spi_flash_probe(0, 0, 0, 0);
+
+	return elog_spi ? 0 : -1;
+}
+
+/*
+ * Clear the entire event log
+ */
+int elog_clear(void)
+{
+	struct elog_descriptor *flash = elog_get_flash();
+
+	elog_debug("elog_clear()\n");
+
+	/* Erase flash area */
+	elog_flash_erase_area();
+
+	/* Prepare new empty area */
+	elog_prepare_empty(flash, NULL, 0);
+
+	/* Update memory area from flash */
+	if (elog_sync_flash_to_mem() < 0)
+		return -1;
+
+	/* Log the clear event */
+	elog_add_event_word(ELOG_TYPE_LOG_CLEAR, flash->total_size);
+
+	return 0;
+}
+
+/*
+ * Event log main entry point
+ */
+int elog_init(void)
+{
+	if (elog_initialized)
+		return 0;
+
+	elog_debug("elog_init()\n");
+
+	/* Find SPI flash chip for backing store */
+	if (elog_spi_init() < 0) {
+		printk(BIOS_ERR, "ELOG: Unable to find SPI flash\n");
+		return -1;
+	}
+
+	/* Setup descriptors for flash and memory areas */
+	if (elog_setup_descriptors(CONFIG_ELOG_FLASH_BASE,
+				   CONFIG_ELOG_AREA_SIZE) < 0) {
+		printk(BIOS_ERR, "ELOG: Unable to initialize descriptors\n");
+		return -1;
+	}
+
+	/* Bootstrap the flash area */
+	if (elog_flash_area_bootstrap() < 0) {
+		printk(BIOS_ERR, "ELOG: Unable to bootstrap flash area\n");
+		return -1;
+	}
+
+	/* Initialize the memory area */
+	if (elog_sync_flash_to_mem() < 0) {
+		printk(BIOS_ERR, "ELOG: Unable to initialize memory area\n");
+		return -1;
+	}
+
+	elog_initialized = 1;
+
+	printk(BIOS_INFO, "ELOG: MEM @0x%p FLASH @0x%p\n",
+	       elog_get_mem()->backing_store,
+	       elog_get_flash()->backing_store);
+
+	printk(BIOS_INFO, "ELOG: areas are %d bytes, full threshold %d,"
+	       " shrink size %d\n", CONFIG_ELOG_AREA_SIZE,
+	       CONFIG_ELOG_FULL_THRESHOLD, CONFIG_ELOG_SHRINK_SIZE);
+
+	/* Log a clear event if necessary */
+	if (elog_get_flash()->event_count == 0)
+		elog_add_event_word(ELOG_TYPE_LOG_CLEAR,
+				    elog_get_flash()->total_size);
+
+	return 0;
+}
+
+/*
+ * Populate timestamp in event header with current time
+ */
+static void elog_fill_timestamp(struct event_header *event)
+{
+	event->second = cmos_read(RTC_CLK_SECOND);
+	event->minute = cmos_read(RTC_CLK_MINUTE);
+	event->hour   = cmos_read(RTC_CLK_HOUR);
+	event->day    = cmos_read(RTC_CLK_DAYOFMONTH);
+	event->month  = cmos_read(RTC_CLK_MONTH);
+	event->year   = cmos_read(RTC_CLK_YEAR);
+
+	/* Basic sanity check of expected ranges */
+	if (event->month > 0x12 || event->day > 0x31 || event->hour > 0x23 ||
+	    event->minute > 0x59 || event->second > 0x59) {
+		event->year   = 0;
+		event->month  = 0;
+		event->day    = 0;
+		event->hour   = 0;
+		event->minute = 0;
+		event->second = 0;
+	}
+}
+
+/*
+ * Add an event to the memory area
+ */
+static int elog_add_event_mem(u8 event_type, void *data, u8 data_size)
+{
+	struct event_header *event;
+	struct elog_descriptor *mem = elog_get_mem();
+	u8 event_size;
+
+	elog_debug("elog_add_event_mem(type=%X)\n", event_type);
+
+	/* Make sure ELOG structures are initialized */
+	if (elog_init() < 0)
+		return -1;
+
+	/* Header + Data + Checksum */
+	event_size = sizeof(*event) + data_size + 1;
+	if (event_size > MAX_EVENT_SIZE) {
+		printk(BIOS_ERR, "ELOG: Event(%X) data size too "
+		       "big (%d)\n", event_type, event_size);
+		return -1;
+	}
+
+	/* Make sure event data can fit */
+	if ((mem->next_event_offset + event_size) >= mem->data_size) {
+		printk(BIOS_ERR, "ELOG: Event(%X) does not fit\n",
+		       event_type);
+		return -1;
+	}
+
+	/* Fill out event data */
+	event = elog_get_next_event_base(mem);
+	event->type = event_type;
+	event->length = event_size;
+	elog_fill_timestamp(event);
+
+	if (data_size)
+		memcpy(&event[1], data, data_size);
+
+	/* Zero the checksum byte and then compute checksum */
+	elog_update_checksum(event, 0);
+	elog_update_checksum(event, -(elog_checksum_event(event)));
+
+	/* Update memory descriptor parameters */
+	mem->event_count++;
+	mem->last_event_offset = mem->next_event_offset;
+	mem->last_event_size = event_size;
+	mem->next_event_offset += event_size;
+
+	printk(BIOS_INFO, "ELOG: Event(%X) added with size %d\n",
+	       event_type, event_size);
+	return 0;
+}
+
+void elog_add_event_raw(u8 event_type, void *data, u8 data_size)
+{
+	elog_debug("elog_add_event_raw(type=%X)\n", event_type);
+
+	/* Add event to the memory area */
+	if (elog_add_event_mem(event_type, data, data_size) < 0) {
+		printk(BIOS_ERR, "Unable to add event to memory area\n");
+		return;
+	}
+
+	/* Sync the memory buffer to flash */
+	elog_sync_mem_to_flash();
+
+	/* Shrink the log if we are getting too full */
+	if (elog_get_mem()->next_event_offset >= CONFIG_ELOG_FULL_THRESHOLD)
+		elog_shrink();
+}
+
+void elog_add_event(u8 event_type)
+{
+	elog_add_event_raw(event_type, NULL, 0);
+}
+
+void elog_add_event_byte(u8 event_type, u8 data)
+{
+	elog_add_event_raw(event_type, &data, sizeof(data));
+}
+
+void elog_add_event_word(u8 event_type, u16 data)
+{
+	elog_add_event_raw(event_type, &data, sizeof(data));
+}
+
+void elog_add_event_dword(u8 event_type, u32 data)
+{
+	elog_add_event_raw(event_type, &data, sizeof(data));
+}
+
+void elog_add_event_wake(u8 source, u32 instance)
+{
+	struct elog_event_data_wake wake = {
+		.source = source,
+		.instance = instance
+	};
+	elog_add_event_raw(ELOG_TYPE_WAKE_SOURCE, &wake, sizeof(wake));
+}
diff --git a/src/drivers/elog/elog_internal.h b/src/drivers/elog/elog_internal.h
new file mode 100644
index 0000000000..2a6a0b7fc4
--- /dev/null
+++ b/src/drivers/elog/elog_internal.h
@@ -0,0 +1,76 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2012 The ChromiumOS Authors.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA, 02110-1301 USA
+ */
+
+#ifndef ELOG_INTERNAL_H_
+#define ELOG_INTERNAL_H_
+
+/* ELOG header */
+struct elog_header {
+	u32 magic;
+	u8 version;
+	u8 header_size;
+	u8 reserved[2];
+} __attribute__ ((packed));
+
+/* ELOG related constants */
+#define ELOG_SIGNATURE			0x474f4c45  /* 'ELOG' */
+#define ELOG_VERSION			1
+
+typedef enum elog_descriptor_type {
+	ELOG_DESCRIPTOR_UNKNOWN,
+	ELOG_DESCRIPTOR_MEMORY,
+	ELOG_DESCRIPTOR_FLASH,
+} elog_descriptor_type;
+
+typedef enum elog_area_state {
+	ELOG_AREA_UNDEFINED,		/* Initial boot strap state */
+	ELOG_AREA_EMPTY,		/* Entire area is empty */
+	ELOG_AREA_HAS_CONTENT,		/* Area has some content */
+} elog_area_state;
+
+typedef enum elog_header_state {
+	ELOG_HEADER_INVALID,
+	ELOG_HEADER_VALID,
+} elog_header_state;
+
+typedef enum elog_event_buffer_state {
+	ELOG_EVENT_BUFFER_OK,
+	ELOG_EVENT_BUFFER_CORRUPTED,
+} elog_event_buffer_state;
+
+/*
+ * Internal handler for event log buffers
+ */
+struct elog_descriptor {
+	elog_descriptor_type	type;
+	elog_area_state		area_state;
+	elog_header_state	header_state;
+	elog_event_buffer_state	event_buffer_state;
+	struct elog_header	*staging_header;
+	void                    *backing_store;
+	u8			*data;
+	u16                     total_size;
+	u16			data_size;
+	u16			next_event_offset;
+	u16			last_event_offset;
+	u16			last_event_size;
+	u16			event_count;
+};
+
+#endif /* ELOG_INTERNAL_H_ */