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authorMike Dunn <mikedunn@newsguy.com>2012-04-25 23:06:08 +0400
committerDavid Woodhouse <David.Woodhouse@intel.com>2012-05-14 08:11:39 +0400
commitd062d4ede877fcd2ecc4c6262abad09a6f32950a (patch)
tree320869428d5aef43b803c4a8131140aabb21c8fb
parenta9b672e82bca47bf2b37ee869b8095000cf3ca88 (diff)
downloadlinux-d062d4ede877fcd2ecc4c6262abad09a6f32950a.tar.xz
mtd: bitflip_threshold added to mtd_info and sysfs
An element 'bitflip_threshold' is added to struct mtd_info, and also exposed as a read/write variable in sysfs. This will be used to determine whether or not mtd_read() returns -EUCLEAN or 0 (absent a hard error). If the driver leaves it as zero, mtd will set it to a default value of ecc_strength. This v2 adds the line that propagates bitflip_threshold from the master to the partitions - thanks Ivan¹. ¹ http://lists.infradead.org/pipermail/linux-mtd/2012-April/040900.html Signed-off-by: Mike Dunn <mikedunn@newsguy.com> Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com> Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
-rw-r--r--Documentation/ABI/testing/sysfs-class-mtd36
-rw-r--r--drivers/mtd/mtdcore.c33
-rw-r--r--drivers/mtd/mtdpart.c2
-rw-r--r--include/linux/mtd/mtd.h9
4 files changed, 80 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-class-mtd b/Documentation/ABI/testing/sysfs-class-mtd
index 43d18180b46e..78835080856a 100644
--- a/Documentation/ABI/testing/sysfs-class-mtd
+++ b/Documentation/ABI/testing/sysfs-class-mtd
@@ -135,3 +135,39 @@ Description:
have multiple ecc steps within each writesize region.
In the case of devices lacking any ECC capability, it is 0.
+
+What: /sys/class/mtd/mtdX/bitflip_threshold
+Date: April 2012
+KernelVersion: 3.4
+Contact: linux-mtd@lists.infradead.org
+Description:
+ This allows the user to examine and adjust the criteria by which
+ mtd returns -EUCLEAN from mtd_read(). If the maximum number of
+ bit errors that were corrected on any single region comprising
+ an ecc step (as reported by the driver) equals or exceeds this
+ value, -EUCLEAN is returned. Otherwise, absent an error, 0 is
+ returned. Higher layers (e.g., UBI) use this return code as an
+ indication that an erase block may be degrading and should be
+ scrutinized as a candidate for being marked as bad.
+
+ The initial value may be specified by the flash device driver.
+ If not, then the default value is ecc_strength.
+
+ The introduction of this feature brings a subtle change to the
+ meaning of the -EUCLEAN return code. Previously, it was
+ interpreted to mean simply "one or more bit errors were
+ corrected". Its new interpretation can be phrased as "a
+ dangerously high number of bit errors were corrected on one or
+ more regions comprising an ecc step". The precise definition of
+ "dangerously high" can be adjusted by the user with
+ bitflip_threshold. Users are discouraged from doing this,
+ however, unless they know what they are doing and have intimate
+ knowledge of the properties of their device. Broadly speaking,
+ bitflip_threshold should be low enough to detect genuine erase
+ block degradation, but high enough to avoid the consequences of
+ a persistent return value of -EUCLEAN on devices where sticky
+ bitflips occur. Note that if bitflip_threshold exceeds
+ ecc_strength, -EUCLEAN is never returned by the read functions.
+
+ This is generally applicable only to NAND flash devices with ECC
+ capability. It is ignored on devices lacking ECC capability.
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 090e849d3dcd..6a7cba1e24e6 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -259,6 +259,34 @@ static ssize_t mtd_ecc_strength_show(struct device *dev,
}
static DEVICE_ATTR(ecc_strength, S_IRUGO, mtd_ecc_strength_show, NULL);
+static ssize_t mtd_bitflip_threshold_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct mtd_info *mtd = dev_get_drvdata(dev);
+
+ return snprintf(buf, PAGE_SIZE, "%u\n", mtd->bitflip_threshold);
+}
+
+static ssize_t mtd_bitflip_threshold_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct mtd_info *mtd = dev_get_drvdata(dev);
+ unsigned int bitflip_threshold;
+ int retval;
+
+ retval = kstrtouint(buf, 0, &bitflip_threshold);
+ if (retval)
+ return retval;
+
+ mtd->bitflip_threshold = bitflip_threshold;
+ return count;
+}
+static DEVICE_ATTR(bitflip_threshold, S_IRUGO | S_IWUSR,
+ mtd_bitflip_threshold_show,
+ mtd_bitflip_threshold_store);
+
static struct attribute *mtd_attrs[] = {
&dev_attr_type.attr,
&dev_attr_flags.attr,
@@ -270,6 +298,7 @@ static struct attribute *mtd_attrs[] = {
&dev_attr_numeraseregions.attr,
&dev_attr_name.attr,
&dev_attr_ecc_strength.attr,
+ &dev_attr_bitflip_threshold.attr,
NULL,
};
@@ -332,6 +361,10 @@ int add_mtd_device(struct mtd_info *mtd)
mtd->index = i;
mtd->usecount = 0;
+ /* default value if not set by driver */
+ if (mtd->bitflip_threshold == 0)
+ mtd->bitflip_threshold = mtd->ecc_strength;
+
if (is_power_of_2(mtd->erasesize))
mtd->erasesize_shift = ffs(mtd->erasesize) - 1;
else
diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index 9651c06de0a9..ec75d44e0253 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -517,6 +517,8 @@ static struct mtd_part *allocate_partition(struct mtd_info *master,
slave->mtd.ecclayout = master->ecclayout;
slave->mtd.ecc_strength = master->ecc_strength;
+ slave->mtd.bitflip_threshold = master->bitflip_threshold;
+
if (master->_block_isbad) {
uint64_t offs = 0;
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index cd0119d19cd9..63dadc0dfb62 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -157,6 +157,15 @@ struct mtd_info {
unsigned int erasesize_mask;
unsigned int writesize_mask;
+ /*
+ * read ops return -EUCLEAN if max number of bitflips corrected on any
+ * one region comprising an ecc step equals or exceeds this value.
+ * Settable by driver, else defaults to ecc_strength. User can override
+ * in sysfs. N.B. The meaning of the -EUCLEAN return code has changed;
+ * see Documentation/ABI/testing/sysfs-class-mtd for more detail.
+ */
+ unsigned int bitflip_threshold;
+
// Kernel-only stuff starts here.
const char *name;
int index;