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@@ -123,3 +123,55 @@ Description:
half page, or a quarter page).
In the case of ECC NOR, it is the ECC block size.
+
+What: /sys/class/mtd/mtdX/ecc_strength
+Date: April 2012
+KernelVersion: 3.4
+Contact: linux-mtd@lists.infradead.org
+Description:
+ Maximum number of bit errors that the device is capable of
+ correcting within each region covering an ecc step. This will
+ always be a non-negative integer. Note that some devices will
+ 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() and mtd_read_oob(). 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 operations.
+ Conversely, if bitflip_threshold is zero, -EUCLEAN is always
+ returned, absent a hard error.
+
+ This is generally applicable only to NAND flash devices with ECC
+ capability. It is ignored on devices lacking ECC capability;
+ i.e., devices for which ecc_strength is zero.