[PATCHv3] ARM:boot:device tree: Allow the device tree binary to be appended to zImage

[Nicolas Pitre]

On Fri, 29 Apr 2011, Russell King - ARM Linux wrote:

> On Fri, Apr 29, 2011 at 09:16:39AM -0400, Nicolas Pitre wrote:
> > On Fri, 29 Apr 2011, Tony Lindgren wrote:
> > 
> > > If the compressed image is smaller than BSS, then we end up
> > > having DT data in the BSS area. In this case the compressed
> > > image is about 2.3 MB for LZMA.
> > > 
> > > The uncompress code does not know about the kernel BSS,
> > > and does not necessarily relocate anything depending on the
> > > compressed image load address.
> > > 
> > > So in which code do we want to relocate the DT data?
> > > 
> > > We could do it based on estimated BSS size in uncompress code,
> > > or based on the real BSS size in __mmap_switched before BSS
> > > gets reset.
> > 
> > Estimations for that kind of thing is always bound to create problems 
> > some day.
> > 
> > The DT data should probably be moved out of the way from 
> > arch/arm/kernel/head.S before the .bss is cleared, and even before 
> > enabling the MMU, like in __vet_atags.
> 
> Err, no.  Moving stuff around becomes quite expensive when the cache is
> not on.  It's far better to work out where to place it first time around
> so its not in the way.

I don't think the DT data is that huge, but that's a point in favor of 
doing it in the zImage code.  We'll just need to feed the total size of 
the uncompressed kernel .bss section to zImage when compiling it.


Nicolas