FT u-boot shim

[Paul Mackerras]

Kumar Gala writes:

> If we have a u-boot shim there are some questions that need answering:
> * where should the .dts live (hate duplicating the file both in u- 
> boot and kernel source tree)
> * how does build system find .dts
> * a Kconfig option to enable shim
> * assume done as a boot wrapper of sorts

What I think would be useful is a stand-alone tool that would take a
kernel and a dts and construct an image that is bootable on a given
board by its existing firmware.  That means there would either need to
be a version of the tool for each firmware, or alternatively a set of
command-line options to tell it what sort of firmware you have.

This wouldn't have to be done at kernel build time; it could be
potentially be done much later.  Hopefully then the board vendors
could take on the job of generating the dts.  In fact for some boards
the board-support package could be just the dts.

This tool would need to insert a suitable shim, which might actually
need to contain code to pull stuff out of a firmware-specific
structure such as a bd_t, and stuff it into the dts.  That should be
doable provided there is a convention about labels in the dts for
things such as memory size, ethernet mac address, etc.

Clearly it is neater if the firmware can supply the device-tree blob
directly, and just boot a raw kernel.  However, there will always be
situations where we don't get to choose the firmware, so I think we
need this tool.

Paul.