On Wednesday 08 June 2011 09:15:14 Geert Uytterhoeven wrote:

On Wed, Jun 8, 2011 at 01:02, David VomLehn [off-list ref] wrote:

quoted

I took a look at the issue of passing device trees to the kernel and
started by surveying the methods currently in use for passing
information from the bootloader to the kernel. I came up with the ten
approaches:

How MIPS Bootloaders Pass Information to the Kernel
---------------------------------------------------
Apologies for any errors; this was meant more to be a quick survey
rather than a detailed analysis.

6.      a0 - argc
       a1 - argv
       a2 - non-standard envp
       Command line created by concatenating argv strings, starting at
       argv[1]. The envp is a pointer to a list of char ptr to name/char
       ptr pairs.
       Platforms: txx9

This depends on the actual boot loader. My rbtx4927 has a VxWorks boot
loader, which just doesn't pass anything.

Cfr. commit 97b0511ce125b0cb95d73b198c1bdbb3cebc4de2 ("MIPS: TXx9:
Make firmware parameter passing more robust").

Thinking about this more, on platforms for which we do not have control about 
the bootloader, we can usually still get it to boot a wrapper. Such a wrapper 
could do the following:

- embedd the kernel
- embedd the appropriate dtb
- copy the relevant a0-a3 values and pass to the kernel a pointer to the valid 
dtb in the aX register

such a wrapper already exists, which is the code responsible for decompressing 
the kernel in arch/mips/boot/compressed.

If we want to support multiple flavors of the same SoC, using the same kernel 
image, we only need to relink the boot wrapper with the correct dtb (and 
kernel of course).
--
Florian