mtd: nand: omap: add CONFIG_SYS_NAND_BUSWIDTH_16BIT to indicate NAND device bus-width

[karo-tx-uboot.git] / doc / README.nand

diff --git a/doc/README.nand b/doc/README.nand
index b91f1985d183d0c3681567293cae7d666139a441..2bc5b391f8011956d613a5671142e0cbeaf6dbe4 100644 (file)
--- 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
 =========================