[PATCH 0/5] Makefile.boot cleanup

[Nicolas Pitre]

On Thu, 3 Jun 2010, Uwe Kleine-König wrote:

> Hello Eric,
> 
> On Thu, Jun 03, 2010 at 03:36:48PM +0800, Eric Miao wrote:
> > Several facts:
> > 
> > 1. ZRELADDR in most cases can be auto detected by maksing PC with
> >    0xf000_0000 if the zImage is placed within the first 256MiB from
> >    the memory start, which is a sane assumption except for:
> > 
> >    - when ARCH_MX1 or ARCH_SHARK is defined
> >    - when ARCH_U300 is defined (U300 really is strange when defining
> >      PHYS_OFFSET and ZRELADDR)
> >    - or when ZBOOT_ROM is defined
> If you guess ZRELADDR based on sp instead of pc it even should work if
> ZBOOT_ROM is defined?!

What is the relation between sp and ZRELADDR?

While we're pushing forward the notion of a relation between phys offset 
and the location where zImage is loaded in memory, I think that making 
the association with sp is a bit too obscur.  Knowing where you upload 
your kernel is clear, knowing where the stack is allocated in relation 
to that is not that clear.  It is in the .bss section of course, but 
when ZBOOT_ROM is not defined then the .bss happens to be right after 
the zImage binary, while it must be explicitly specified otherwise.

On Sun, 6 Jun 2010, Uwe Kleine-König wrote:

> On Thu, Jun 10, 2010 at 02:44:53PM -0400, Nicolas Pitre wrote:
> > If you're using ZBOOT_ROM that means you want to execute zImage directly
> > from ROM.  This is therefore a highly customized configuration.  In that
> > context, having a variable phys-offset doesn't make much sense to start
> > with.
> Right, but then the kernel needs to know this fixed value for
> phys-offset.  In the patches presented by Eric the person configuring
> the kernel needs to know that value.  When guessing based on sp she
> doesn't need to read addional docs when enabling ZBOOT_ROM.

That's presuming phys offset would still be runtime determined.  Again, 
if you care about ZBOOT_ROM, you probably want a fixed phys offset at 
compile time too.  So that value has to be determined at kernel config 
time, not at run time from pc or sp.  And when dealing with such 
customized expert config options, she better know what she's doing and 
be familiar with the memory layout so not to have to read the datasheet 
only for the physical RAM offset while she already must know what flash 
offset to use.

If anything, you _could_ try doing something similar to:

config PHYS_OFFSET
	[prompt]
	default (CONFIG_ZBOOT_ROM_BSS & 0xf0000000) if ZBOOT_ROM

but I doubt Kconfig might accept such a syntax.


Nicolas