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
  ...

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.