[U-Boot] Some thoughts on SPL

[Scott Wood <scottwood@freescale.com>]

On 12/16/2011 11:20 AM, jonsmirl at gmail.com wrote:
> The CPU I'm working with, the LPC3130, is kind of an in-between CPU
> for SPL. Instead of a tightly constrained RAM of 16KB or so I have

16K?  Luxury! :-)

Many boards have only 4K, and IIRC some have only 2K.

> 96KB to work with.  96KB is enough room to support all of the various
> boot modes (uart, nand, spi, USB, etc) but not enough room for the
> full uboot command set. So I'm still stuck with the SPL model, but my
> constraints are much less.

All the SPL model is really supposed to be is makefile infrastructure
for building the two stages.  What code you pull in is configurable.

> One example of a conflict with SPL is NAND support. With SPL you hard
> code in the NAND type.

This is only required with nand_spl_simple.c.

You could provide an alternate SPL driver, or even pull in the standard
SPL stack if you want.  No need to hack up nand_spl_simple.c.

> I'm wondering if SPL could be designed in a more generic manner.
> Another model would be to use SPL as the base layer for all u-boot
> builds. You would then start turning on features until full uboot
> capability was reached.

A while back I suggested tracking a fully separate config for SPL, but
Wolfgang didn't like it.  Maybe a larger set of concrete use cases (and
what it looks like to deal with each one manually as would currently be
needed) would be convincing -- at the time it was just about having a
separate CONFIG_SYS_TEXT_BASE_SPL.

-Scott