[U-Boot-Users] [rfc] new spiflash subsystem

[Mike Frysinger <vapier@gentoo.org>]

this isnt against u-boot mainline, so there will be a few things that are out 
of date (like the CFG handling), so over look that part.  what's up for 
comments here is the general architecture.  ive omitted the env_spiflash.c 
portion as i think that'll be pretty cheesy.

basically ive laid it out like so:
 - common/cmd_spiflash.c:
provides the user interface of the spiflash subsystem.  depends on these 
functions being implemented elsewhere:
	* spiflash_info() - ask the spiflash driver for info
	* spiflash_read() - ask the spiflash driver to read
	* spiflash_write() - ask the spiflash driver to write
	* spiflash_erase() - ask the spiflash driver to erase
no validation occurs in the common code since it has no idea about sector 
sizes and such.  i could add a spiflash_query() function and have it return a 
struct describing the spiflash and use that to validate, but i dont think 
it's really worth the effort.
relevant defines:
	* CFG_CMD_SPIFLASH - include the "spiflash" command
	* CFG_SPIFLASH_MULTI - support multiple parts (via "cs" parameter)

 - drivers/mtd/spiflash_jedec.c:
provides the spiflash driver functions needed by the common layer.  detects 
and works with Spansion/ST/Atmel/Winbond parts.  i've personally verified at 
least one part from each family, but obviously not every part ;).  it depends 
on these functions being implemented elsewhere:
	* spiflash_on() - turn on the SPI
	* spiflash_off() - turn off the SPI
	* spiflash_cs_set() - assert/deassert the specified chip select
	* spiflash_exchange_byte() - send specified byte and return received byte
relevant defines:
	* CFG_SPIFLASH_JEDEC_DRIVER - enable this driver
	* CFG_SPIFLASH_MULTI - disable a small runtime opt to avoid redetection

 - board/$BOARD/spiflash.c:
provides the board / cpu specific spiflash functions.  ive included the 
Blackfin one here as an example.

-mike
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