[PATCH] ubi: Update mean Erase Counter calculation at run-time

[Paul HENRYS <paul.henrysd@xxxxxxxxx>]

The mean EC value was only calculated when attaching a UBI device
but not updated afterwards. A new parameter is added to the struct
ubi_device to keep track of the sum of the erase counters of all
eraseblocks for a UBI device while they are erased and potentially
become bad. The mean EC is then calculated on request when reading
the "mean_ec" sysfs file of a UBI device.

Signed-off-by: Paul HENRYS <paul.henrysd@xxxxxxxxx>
---
 drivers/mtd/ubi/build.c | 10 ++++++++++
 drivers/mtd/ubi/ubi.h   |  3 ++-
 drivers/mtd/ubi/wl.c    |  5 +++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index d636bbe..3291fa4 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -126,6 +126,8 @@ static struct device_attribute dev_volumes_count =
 	__ATTR(volumes_count, S_IRUGO, dev_attribute_show, NULL);
 static struct device_attribute dev_max_ec =
 	__ATTR(max_ec, S_IRUGO, dev_attribute_show, NULL);
+static struct device_attribute dev_mean_ec =
+	__ATTR(mean_ec, S_IRUGO, dev_attribute_show, NULL);
 static struct device_attribute dev_reserved_for_bad =
 	__ATTR(reserved_for_bad, S_IRUGO, dev_attribute_show, NULL);
 static struct device_attribute dev_bad_peb_count =
@@ -364,6 +366,13 @@ static ssize_t dev_attribute_show(struct device *dev,
 		ret = sprintf(buf, "%d\n", ubi->vol_count - UBI_INT_VOL_COUNT);
 	else if (attr == &dev_max_ec)
 		ret = sprintf(buf, "%d\n", ubi->max_ec);
+	else if (attr == &dev_mean_ec) {
+		/* Calculate mean erase counter */
+		if (ubi->good_peb_count)
+			ubi->mean_ec = div_u64(ubi->ec_sum,
+						ubi->good_peb_count);
+		ret = sprintf(buf, "%d\n", ubi->mean_ec);
+	}
 	else if (attr == &dev_reserved_for_bad)
 		ret = sprintf(buf, "%d\n", ubi->beb_rsvd_pebs);
 	else if (attr == &dev_bad_peb_count)
@@ -391,6 +400,7 @@ static struct attribute *ubi_dev_attrs[] = {
 	&dev_total_eraseblocks.attr,
 	&dev_volumes_count.attr,
 	&dev_max_ec.attr,
+	&dev_mean_ec.attr,
 	&dev_reserved_for_bad.attr,
 	&dev_bad_peb_count.attr,
 	&dev_max_vol_count.attr,
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index 9688b41..d796217 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -472,6 +472,7 @@ struct ubi_debug_info {
  *
  * @max_ec: current highest erase counter value
  * @mean_ec: current mean erase counter value
+ * @ec_sum: a temporary variable used when calculating @mean_ec
  *
  * @global_sqnum: global sequence number
  * @ltree_lock: protects the lock tree and @global_sqnum
@@ -580,8 +581,8 @@ struct ubi_device {
 	struct mutex device_mutex;
 
 	int max_ec;
-	/* Note, mean_ec is not updated run-time - should be fixed */
 	int mean_ec;
+	uint64_t ec_sum;
 
 	/* EBA sub-system's stuff */
 	unsigned long long global_sqnum;
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 5d77a38..24c47ce 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -442,6 +442,7 @@ static int sync_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
 	int err;
 	struct ubi_ec_hdr *ec_hdr;
 	unsigned long long ec = e->ec;
+	unsigned long long erasecycle;
 
 	dbg_wl("erase PEB %d, old EC %llu", e->pnum, ec);
 
@@ -458,6 +459,7 @@ static int sync_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
 		goto out_free;
 
 	ec += err;
+	erasecycle = err;
 	if (ec > UBI_MAX_ERASECOUNTER) {
 		/*
 		 * Erase counter overflow. Upgrade UBI and use 64-bit
@@ -479,6 +481,7 @@ static int sync_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
 
 	e->ec = ec;
 	spin_lock(&ubi->wl_lock);
+	ubi->ec_sum += erasecycle;
 	if (e->ec > ubi->max_ec)
 		ubi->max_ec = e->ec;
 	spin_unlock(&ubi->wl_lock);
@@ -1164,6 +1167,7 @@ static int __erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk)
 	}
 	ubi->bad_peb_count += 1;
 	ubi->good_peb_count -= 1;
+	ubi->ec_sum -= e->ec;
 	ubi_calculate_reserved(ubi);
 	if (available_consumed)
 		ubi_warn(ubi, "no PEBs in the reserved pool, used an available PEB");
@@ -1738,6 +1742,7 @@ int ubi_wl_init(struct ubi_device *ubi, struct ubi_attach_info *ai)
 	mutex_init(&ubi->move_mutex);
 	init_rwsem(&ubi->work_sem);
 	ubi->max_ec = ai->max_ec;
+	ubi->ec_sum = ai->ec_sum;
 	INIT_LIST_HEAD(&ubi->works);
 
 	sprintf(ubi->bgt_name, UBI_BGT_NAME_PATTERN, ubi->ubi_num);
-- 
2.7.4


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