From b80a66033856cc89c62886ae3e5ba54a7faf31ae Mon Sep 17 00:00:00 2001 From: pekon gupta Date: Tue, 6 May 2014 00:46:19 +0530 Subject: mtd: nand: omap: add CONFIG_SYS_NAND_BUSWIDTH_16BIT to indicate NAND device bus-width GPMC controller needs to be configured based on bus-width of the NAND device connected to it. Also, dynamic detection of NAND bus-width from on-chip ONFI parameters is not possible in following situations: SPL: SPL NAND drivers does not support ONFI parameter reading. U-boot: GPMC controller iniitalization is done in omap_gpmc.c:board_nand_init() which is called before probing for devices, hence any ONFI parameter information is not available during GPMC initialization. Thus, OMAP NAND driver expected board developers to explicitely write GPMC configurations specific to NAND device attached on board in board files itself. But this was troublesome for board manufacturers as they need to dive into lengthy platform & SoC documents to find details of GPMC registers and appropriate configurations to get NAND device working. This patch instead adds existing CONFIG_SYS_NAND_BUSWIDTH_16BIT to board config hich indicates that connected NAND device has x16 bus-width. And then based on this config GPMC driver itself initializes itself based on NAND bus-width. This keeps board developers free from knowing GPMC controller specific internals. Signed-off-by: Pekon Gupta --- doc/README.nand | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'doc/README.nand') diff --git a/doc/README.nand b/doc/README.nand index b91f198..2bc5b39 100644 --- a/doc/README.nand +++ b/doc/README.nand @@ -190,6 +190,24 @@ Configuration Options: This is used by SoC platforms which do not have built-in ELM hardware engine required for BCH ECC correction. + CONFIG_SYS_NAND_BUSWIDTH_16BIT + Indicates that NAND device has 16-bit wide data-bus. In absence of this + config, bus-width of NAND device is assumed to be either 8-bit and later + determined by reading ONFI params. + Above config is useful when NAND device's bus-width information cannot + be determined from on-chip ONFI params, like in following scenarios: + - SPL boot does not support reading of ONFI parameters. This is done to + keep SPL code foot-print small. + - In current U-Boot flow using nand_init(), driver initialization + happens in board_nand_init() which is called before any device probe + (nand_scan_ident + nand_scan_tail), thus device's ONFI parameters are + not available while configuring controller. So a static CONFIG_NAND_xx + is needed to know the device's bus-width in advance. + Some drivers using above config are: + drivers/mtd/nand/mxc_nand.c + drivers/mtd/nand/ndfc.c + drivers/mtd/nand/omap_gpmc.c + Platform specific options ========================= -- cgit v1.1 From 867f03040f771a95323925b569eaf3b911b9eb14 Mon Sep 17 00:00:00 2001 From: pekon gupta Date: Mon, 2 Jun 2014 17:14:43 +0530 Subject: am335x: update README for BCH16 updates documentation with explanation on how to select ECC schemes. Signed-off-by: Pekon Gupta --- doc/README.nand | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) (limited to 'doc/README.nand') diff --git a/doc/README.nand b/doc/README.nand index 2bc5b39..70cf768 100644 --- a/doc/README.nand +++ b/doc/README.nand @@ -249,6 +249,48 @@ Platform specific options 8-bit BCH code with - ecc calculation using GPMC hardware engine, - error detection using ELM hardware engine. + OMAP_ECC_BCH16_CODE_HW + 16-bit BCH code with + - ecc calculation using GPMC hardware engine, + - error detection using ELM hardware engine. + + How to select ECC scheme on OMAP and AMxx platforms ? + ----------------------------------------------------- + Though higher ECC schemes have more capability to detect and correct + bit-flips, but still selection of ECC scheme is dependent on following + - hardware engines present in SoC. + Some legacy OMAP SoC do not have ELM h/w engine thus such + SoC cannot support BCHx_HW ECC schemes. + - size of OOB/Spare region + With higher ECC schemes, more OOB/Spare area is required to + store ECC. So choice of ECC scheme is limited by NAND oobsize. + + In general following expression can help: + NAND_OOBSIZE >= 2 + (NAND_PAGESIZE / 512) * ECC_BYTES + where + NAND_OOBSIZE = number of bytes available in + OOB/spare area per NAND page. + NAND_PAGESIZE = bytes in main-area of NAND 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 to check for BCH16 on 2K page NAND + NAND_PAGESIZE = 2048 + NAND_OOBSIZE = 64 + 2 + (2048 / 512) * 26 = 106 > NAND_OOBSIZE + Thus BCH16 cannot be supported on 2K page NAND. + + However, for 4K pagesize NAND + NAND_PAGESIZE = 4096 + NAND_OOBSIZE = 64 + ECC_BYTES = 26 + 2 + (4096 / 512) * 26 = 210 < NAND_OOBSIZE + Thus BCH16 can be supported on 4K page NAND. + NOTE: ===== -- cgit v1.1