elog: Eliminate CONFIG_ELOG_FULL_THRESHOLD and CONFIG_ELOG_SHRINK_SIZE

These Kconfig options provided a level of configurability that is
almost never necessary, so they are being moved into ordinary
preprocessor defines in elog_internal.h. The new threshold to
trigger shrinking is relative to the number of additional
(maximum-size) events that can fit, and the new target
post-shrink size is a percentage of the total ELOG area size.

BUG=chromium:467820
TEST=Add loop at the end of elog_init() that fills the ELOG area
to just below full_threshold with dummy events. Observe
successful shrinkage when the next event is logged.
BRANCH=None

Change-Id: I414c4955a2d819d112ae4f0c7d3571576f732336
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: ce439361e3954a2bf5186292f96936329171cf56
Original-Change-Id: I926097f86262888dcdd47d73fba474bb2e19856a
Original-Signed-off-by: Sol Boucher <solb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/260501
Original-Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Original-Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-on: http://review.coreboot.org/9869
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

3 files changed, 22 insertions, 43 deletions

diff --git a/src/drivers/elog/Kconfig b/src/drivers/elog/Kconfig
index 162cc5f361..7affd0694a 100644
--- a/src/drivers/elog/Kconfig
+++ b/src/drivers/elog/Kconfig
@@ -45,27 +45,6 @@ config ELOG_AREA_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.
-
 config ELOG_CBMEM
 	bool "Store a copy of ELOG in CBMEM"
 	default n
diff --git a/src/drivers/elog/elog.c b/src/drivers/elog/elog.c
index f5135d99a3..de18d5d82f 100644
--- a/src/drivers/elog/elog.c
+++ b/src/drivers/elog/elog.c
@@ -40,19 +40,6 @@
 #if !IS_ENABLED(CONFIG_CHROMEOS) && 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)
@@ -65,14 +52,16 @@
  */
 static struct elog_area *elog_area;
 static u16 total_size;
-static u16 log_size;
+static u16 log_size; /* excluding header */
 static u32 flash_base;
+static u16 full_threshold; /* from end of header */
+static u16 shrink_size; /* from end of header */
 
 static elog_area_state area_state;
 static elog_header_state header_state;
 static elog_event_buffer_state event_buffer_state;
 
-static u16 next_event_offset;
+static u16 next_event_offset; /* from end of header */
 static u16 event_count;
 
 static struct spi_flash *elog_spi;
@@ -402,12 +391,12 @@ static int elog_shrink(void)
 
 	elog_debug("elog_shrink()\n");
 
-	if (next_event_offset < CONFIG_ELOG_SHRINK_SIZE)
+	if (next_event_offset < shrink_size)
 		return 0;
 
 	while (1) {
 		/* Next event has exceeded constraints */
-		if (offset > CONFIG_ELOG_SHRINK_SIZE)
+		if (offset > shrink_size)
 			break;
 
 		event = elog_get_event_base(offset);
@@ -429,7 +418,7 @@ static int elog_shrink(void)
 	elog_scan_flash();
 
 	/* Ensure the area was successfully erased */
-	if (next_event_offset >= CONFIG_ELOG_FULL_THRESHOLD) {
+	if (next_event_offset >= full_threshold) {
 		printk(BIOS_ERR, "ELOG: Flash area was not erased!\n");
 		return -1;
 	}
@@ -544,6 +533,9 @@ static void elog_find_flash(void)
 	total_size = CONFIG_ELOG_AREA_SIZE;
 #endif
 	log_size = total_size - sizeof(struct elog_header);
+	full_threshold = log_size - ELOG_MIN_AVAILABLE_ENTRIES * MAX_EVENT_SIZE;
+	shrink_size = MIN(total_size * ELOG_SHRINK_PERCENTAGE / 100,
+								full_threshold);
 }
 
 /*
@@ -575,6 +567,13 @@ int elog_init(void)
 	if (flash_base == 0) {
 		printk(BIOS_ERR, "ELOG: Invalid flash base\n");
 		return -1;
+	} else if (total_size < sizeof(struct elog_header) + MAX_EVENT_SIZE) {
+		printk(BIOS_ERR, "ELOG: Region too small to hold any events\n");
+		return -1;
+	} else if (log_size - shrink_size >= full_threshold) {
+		printk(BIOS_ERR,
+			"ELOG: SHRINK_PERCENTAGE set too small for MIN_AVAILABLE_ENTRIES\n");
+		return -1;
 	}
 
 	elog_area = malloc(total_size);
@@ -608,13 +607,12 @@ int elog_init(void)
 	       elog_area, flash_base);
 
 	printk(BIOS_INFO, "ELOG: area is %d bytes, full threshold %d,"
-	       " shrink size %d\n", total_size,
-	       CONFIG_ELOG_FULL_THRESHOLD, CONFIG_ELOG_SHRINK_SIZE);
+	       " shrink size %d\n", total_size, full_threshold, shrink_size);
 
 	elog_initialized = ELOG_INITIALIZED;
 
 	/* Shrink the log if we are getting too full */
-	if (next_event_offset >= CONFIG_ELOG_FULL_THRESHOLD)
+	if (next_event_offset >= full_threshold)
 		if (elog_shrink() < 0)
 			return -1;
 
@@ -726,7 +724,7 @@ void elog_add_event_raw(u8 event_type, void *data, u8 data_size)
 	       event_type, event_size);
 
 	/* Shrink the log if we are getting too full */
-	if (next_event_offset >= CONFIG_ELOG_FULL_THRESHOLD)
+	if (next_event_offset >= full_threshold)
 		elog_shrink();
 }
 
diff --git a/src/drivers/elog/elog_internal.h b/src/drivers/elog/elog_internal.h
index dd282311a6..6194ef6c3e 100644
--- a/src/drivers/elog/elog_internal.h
+++ b/src/drivers/elog/elog_internal.h
@@ -31,6 +31,8 @@ struct elog_header {
 /* ELOG related constants */
 #define ELOG_SIGNATURE			0x474f4c45  /* 'ELOG' */
 #define ELOG_VERSION			1
+#define ELOG_MIN_AVAILABLE_ENTRIES	2  /* Shrink when this many can't fit */
+#define ELOG_SHRINK_PERCENTAGE		25 /* Percent of total area to remove */
 
 /* SMBIOS event log header */
 struct event_header {