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;