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authorLinus Torvalds <torvalds@linux-foundation.org>2014-06-11 08:35:34 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-11 08:35:34 -0700
commite413a19a8ef49ae3b76310bb569dabe66b22f5a3 (patch)
treef171d40fd0ec69296458173d7ec470339f93f53b /Documentation/devicetree/bindings/mtd/gpmc-nand.txt
parent8d0304e69dc960ae7683943ac5b9c4c685d409d7 (diff)
parentf1900c79633e9ed757319e63aefb8e29443ea35e (diff)
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Merge tag 'for-linus-20140610' of git://git.infradead.org/linux-mtd
Pull MTD updates from Brian Norris: - refactor m25p80.c driver for use as a general SPI NOR framework for other drivers which may speak to SPI NOR flash without providing full SPI support (i.e., not part of drivers/spi/) - new Freescale QuadSPI driver (utilizing new SPI NOR framework) - updates for the STMicro "FSM" SPI NOR driver - fix sync/flush behavior on mtd_blkdevs - fixup subpage write support on a few NAND drivers - correct the MTD OOB test for odd-sized OOB areas - add BCH-16 support for OMAP NAND - fix warnings and trivial refactoring - utilize new ECC DT bindings in pxa3xx NAND driver - new LPDDR NVM driver - address a few assorted bugs caught by Coverity - add new imx6sx support for GPMI NAND - use a bounce buffer for NAND when non-DMA-able buffers are used * tag 'for-linus-20140610' of git://git.infradead.org/linux-mtd: (77 commits) mtd: gpmi: add gpmi support for imx6sx mtd: maps: remove check for CONFIG_MTD_SUPERH_RESERVE mtd: bf5xx_nand: use the managed version of kzalloc mtd: pxa3xx_nand: make the driver work on big-endian systems mtd: nand: omap: fix omap_calculate_ecc_bch() for-loop error mtd: nand: r852: correct write_buf loop bounds mtd: nand_bbt: handle error case for nand_create_badblock_pattern() mtd: nand_bbt: remove unused variable mtd: maps: sc520cdp: fix warnings mtd: slram: fix unused variable warning mtd: pfow: remove unused variable mtd: lpddr: fix Kconfig dependency, for I/O accessors mtd: nand: pxa3xx: Add supported ECC strength and step size to the DT binding mtd: nand: pxa3xx: Use ECC strength and step size devicetree binding mtd: nand: pxa3xx: Clean pxa_ecc_init() error handling mtd: nand: Warn the user if the selected ECC strength is too weak mtd: nand: omap: Documentation: How to select correct ECC scheme for your device ? mtd: nand: omap: add support for BCH16_ECC - NAND driver updates mtd: nand: omap: add support for BCH16_ECC - ELM driver updates mtd: nand: omap: add support for BCH16_ECC - GPMC driver updates ...
Diffstat (limited to 'Documentation/devicetree/bindings/mtd/gpmc-nand.txt')
-rw-r--r--Documentation/devicetree/bindings/mtd/gpmc-nand.txt45
1 files changed, 45 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
index eb05255..65f4f7c 100644
--- a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
+++ b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
@@ -28,6 +28,8 @@ Optional properties:
"ham1" 1-bit Hamming ecc code
"bch4" 4-bit BCH ecc code
"bch8" 8-bit BCH ecc code
+ "bch16" 16-bit BCH ECC code
+ Refer below "How to select correct ECC scheme for your device ?"
- ti,nand-xfer-type: A string setting the data transfer type. One of:
@@ -90,3 +92,46 @@ Example for an AM33xx board:
};
};
+How to select correct ECC scheme for your device ?
+--------------------------------------------------
+Higher ECC scheme usually means better protection against bit-flips and
+increased system lifetime. However, selection of ECC scheme is dependent
+on various other factors also like;
+
+(1) support of built in hardware engines.
+ Some legacy OMAP SoC do not have ELM harware engine, so those SoC cannot
+ support ecc-schemes with hardware error-correction (BCHx_HW). However
+ such SoC can use ecc-schemes with software library for error-correction
+ (BCHx_HW_DETECTION_SW). The error correction capability with software
+ library remains equivalent to their hardware counter-part, but there is
+ slight CPU penalty when too many bit-flips are detected during reads.
+
+(2) Device parameters like OOBSIZE.
+ Other factor which governs the selection of ecc-scheme is oob-size.
+ Higher ECC schemes require more OOB/Spare area to store ECC syndrome,
+ so the device should have enough free bytes available its OOB/Spare
+ area to accomodate ECC for entire page. In general following expression
+ helps in determining if given device can accomodate ECC syndrome:
+ "2 + (PAGESIZE / 512) * ECC_BYTES" >= OOBSIZE"
+ where
+ OOBSIZE number of bytes in OOB/spare area
+ PAGESIZE number of bytes in main-area of device page
+ ECC_BYTES number of ECC bytes generated to protect
+ 512 bytes of data, which is:
+ '3' for HAM1_xx ecc schemes
+ '7' for BCH4_xx ecc schemes
+ '14' for BCH8_xx ecc schemes
+ '26' for BCH16_xx ecc schemes
+
+ Example(a): For a device with PAGESIZE = 2048 and OOBSIZE = 64 and
+ trying to use BCH16 (ECC_BYTES=26) ecc-scheme.
+ Number of ECC bytes per page = (2 + (2048 / 512) * 26) = 106 B
+ which is greater than capacity of NAND device (OOBSIZE=64)
+ Hence, BCH16 cannot be supported on given device. But it can
+ probably use lower ecc-schemes like BCH8.
+
+ Example(b): For a device with PAGESIZE = 2048 and OOBSIZE = 128 and
+ trying to use BCH16 (ECC_BYTES=26) ecc-scheme.
+ Number of ECC bytes per page = (2 + (2048 / 512) * 26) = 106 B
+ which can be accomodate in the OOB/Spare area of this device
+ (OOBSIZE=128). So this device can use BCH16 ecc-scheme.
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