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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/README.nand | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/doc/README.nand b/doc/README.nand index 023740e..04a87c9 100644 --- a/doc/README.nand +++ b/doc/README.nand @@ -120,6 +120,68 @@ Configuration Options: CONFIG_SYS_NAND_MAX_CHIPS The maximum number of NAND chips per device to be supported. + CONFIG_SYS_NAND_SELF_INIT + Traditionally, glue code in drivers/mtd/nand/nand.c has driven + the initialization process -- it provides the mtd and nand + structs, calls a board init function for a specific device, + calls nand_scan(), and registers with mtd. + + This arrangement does not provide drivers with the flexibility to + run code between nand_scan_ident() and nand_scan_tail(), or other + deviations from the "normal" flow. + + If a board defines CONFIG_SYS_NAND_SELF_INIT, drivers/mtd/nand/nand.c + will make one call to board_nand_init(), with no arguments. That + function is responsible for calling a driver init function for + each NAND device on the board, that performs all initialization + tasks except setting mtd->name, and registering with the rest of + U-Boot. Those last tasks are accomplished by calling nand_register() + on the new mtd device. + + Example of new init to be added to the end of an existing driver + init: + + /* + * devnum is the device number to be used in nand commands + * and in mtd->name. Must be less than + * CONFIG_SYS_NAND_MAX_DEVICE. + */ + mtd = &nand_info[devnum]; + + /* chip is struct nand_chip, and is now provided by the driver. */ + mtd->priv = &chip; + + /* + * Fill in appropriate values if this driver uses these fields, + * or uses the standard read_byte/write_buf/etc. functions from + * nand_base.c that use these fields. + */ + chip.IO_ADDR_R = ...; + chip.IO_ADDR_W = ...; + + if (nand_scan_ident(mtd, CONFIG_SYS_MAX_NAND_CHIPS, NULL)) + error out + + /* + * Insert here any code you wish to run after the chip has been + * identified, but before any other I/O is done. + */ + + if (nand_scan_tail(mtd)) + error out + + if (nand_register(devnum)) + error out + + In addition to providing more flexibility to the driver, it reduces + the difference between a U-Boot driver and its Linux counterpart. + nand_init() is now reduced to calling board_nand_init() once, and + printing a size summary. This should also make it easier to + transition to delayed NAND initialization. + + Please convert your driver even if you don't need the extra + flexibility, so that one day we can eliminate the old mechanism. + NOTE: ===== |