On Wednesday 08 June 2011 09:15:14 Geert Uytterhoeven wrote:
> On Wed, Jun 8, 2011 at 01:02, David VomLehn <dvomlehn@xxxxxxxxx> wrote:
> > 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
