[PATCH] powerpc/bootwrapper: Add documentation of boot wrappertargets

[Scott Wood]

Stephen Neuendorffer wrote:
>> cuImage is for boards running an older U-Boot that does not understand
>> device trees.
> 
> Forgive my ignorance here, but what specifically does this imply?  As
> far as I can tell, generally speaking, some of the board-specific
> information is passed into the boot wrapper, which then stuffs it into
> the device tree.

It implies that the binary is in uImage format, targets older u-boot (as 
opposed to some other bootloader entirely, which might be targeted with 
a dtbImage -- see adder875, for example), and has a device tree embedded.

>> uImage is for device-tree aware U-Boot versions
> 
> And this differs from above because it gets a device tree passed in,
> which uboot has already stuffed correctly.

Yes.

>> dtbImage is used for boards that can take an ELF zImage, but still
> need
>> a dtb provided.
>>
>> simpleImage, not sure here.
> 
> So both of these are elfs...  but how do they differ?  Is it only in how
> the right head.s file gets picked up?

Neither is necessarily an ELF.  The only simpleboot target I see is a 
flat binary, as are some of the dtbImage targets (adder875, ep88xc, 
ep405, etc).  simpleboot is more of a platform than an image type; it's 
a platform that assumes nothing about the firmware that loaded it, and 
gets all information from the embedded device tree.

-Scott