u-boot/doc/README.cfi

The common CFI driver provides this weak default implementation for
flash_cmd_reset():

static void __flash_cmd_reset(flash_info_t *info)
{
	/*
	 * We do not yet know what kind of commandset to use, so we issue
	 * the reset command in both Intel and AMD variants, in the hope
	 * that AMD flash roms ignore the Intel command.
	 */
	flash_write_cmd(info, 0, 0, AMD_CMD_RESET);
	udelay(1);
	flash_write_cmd(info, 0, 0, FLASH_CMD_RESET);
}
void flash_cmd_reset(flash_info_t *info)
	__attribute__((weak,alias("__flash_cmd_reset")));

Some flash chips seem to have trouble with this reset sequence.
In this case, board-specific code can override this weak default
version with a board-specific function.

At the time of writing, there are two boards that define their own
routine for this.

First, the digsy_mtc board equipped with the M29W128GH from Numonyx
needs this version to function properly:

void flash_cmd_reset(flash_info_t *info)
{
	flash_write_cmd(info, 0, 0, AMD_CMD_RESET);
}

In addition, the t3corp board defines the routine thusly:

void flash_cmd_reset(flash_info_t *info)
{
	/*
	 * FLASH at address CFG_SYS_FLASH_BASE is a Spansion chip and
	 * needs the Spansion type reset commands. The other flash chip
	 * is located behind a FPGA (Xilinx DS617) and needs the Intel type
	 * reset command.
	 */
	if (info->start[0] == CFG_SYS_FLASH_BASE)
		flash_write_cmd(info, 0, 0, AMD_CMD_RESET);
	else
		flash_write_cmd(info, 0, 0, FLASH_CMD_RESET);
}

see also:
http://www.mail-archive.com/u-boot@lists.denx.de/msg24368.html


Config Option

  CONFIG_SYS_MAX_FLASH_SECT: Number of sectors available on Flash device

  CONFIG_SYS_FLASH_CFI_WIDTH: Data-width of the flash device

  CONFIG_CMD_FLASH: Enables Flash command library

  CONFIG_FLASH_CFI_DRIVER: Enables CFI Flash driver

  CONFIG_FLASH_CFI_MTD: Enables MTD frame work for NOR Flash devices