[U-Boot] Falcon mode boot support

[Andy Pont <andy.pont@sdcsystems.com>]

Hi Tom,

> eMMC is likely to be faster, yes.  You may also want to see what can be
> trimmed from the kernel binary, in either case, and if going with an
> uncompressed kernel ends up being quicker.

There are I think two issues going on here one with decompression time
which, as you say, I can resolve by using an uncompressed kernel.  The other
is with the SPI transfer time and some testing has shown that if I boot to
U-Boot and then run:

U-Boot> time sf read ${loadaddr} 0x200000 ${loadsize}

I get the following back:

SF: 2541352 bytes @ 0x200000 Read: OK
time: 2.447 seconds

The Spansion datasheet states that in read mode it can transfer 6.25Mbytes/s
in standard read mode at 50MHz clock.  I have the clock at 40MHz as the
device on the other SPI interface won't support anything faster.

When I tested this on the Starter Kit reference board and again on the
target hardware I had to increase the value of SPI_WAIT_TIMEOUT in
driver/spi/omap3_spi.c from 3000000 by adding an extra '0' in order to stop
getting read failures with "sf read" commands with more than about 2MB of
data as per the discussion on the TI E2E community here:
http://e2e.ti.com/support/arm/sitara_arm/f/791/p/366019/1293837.aspx#1293837
.

Regards,

Andy.