[U-Boot] [RFC] Supporting multiple variants of an SoC

[Stephen Warren <swarren@wwwdotorg.org>]

On 07/02/2013 10:28 AM, Tom Rini wrote:
> Hey guys,
> 
> I'm wondering about something and looking for input.  As has come
> up a few times now, we have the ability for a single binary to run
> on a few systems (there's both i.MX examples and AM335x examples),
> but what we don't have is agreement on the best way to handle
> things that must (today) be done at build time.  For example,
> am335x_evm supports both the "kitchen sink" style EVM which
> includes NAND, and Beaglebone White/Black, which do not.  But we
> default to env on NAND as that was the first board up.  What might
> provide the best end-user experience (in their binary) would be
> adding a build target of am335x_evm_bbb that: - Uses eMMC for
> environment - Uses GPIO (since we have a button available) for
> skipping Falcon Mode and then adding am335x_evm_sd_only that: -
> Uses a file on FAT for environment - Uses a character (c) for
> skipping Falcon Mode and maybe even adding am335x_evm_nand that: -
> Uses NAND for environment (still default) - Checks environment for
> skipping Falcon Mode
> 
> That said, when others have suggested something like this before, 
> Wolfgang has pointed out and NAK'd the idea of adding N different 
> configuration as that adds (potentially) a lot of build time for 
> custodians/etc that tend to build --soc or --arch or other group 
> targets.  So, what do we want to do here?  I guess longer term, if
> we are able to focus on switching to Kconfig, it would become we
> provide a generic defconfig for am335x (or imx6 or ...) with a
> best-fit-for-all set and communities can provide tweaked binaries
> as needed.  But do we want to think about any stop-gap solutions
> here?

Can there be a single generic binary, which is configured at run-time
by device-tree? Tegra and at least some Samsung Exynos boards (snow I
guess) seem headed that way, although the conversion is nowhere near
complete and hasn't yet covered the specific differences you listed above.