[U-Boot] [RFC] ARM ISA/cpu/SoC code organization for cache and other functions

[Jason]

On Thu, Sep 15, 2011 at 07:10:49PM -0400, Jason wrote:
> Albert,
> 
> On Thu, Sep 15, 2011 at 11:42:12PM +0200, Albert ARIBAUD wrote:
> > (re-posting cleaned up and outside any other discussion)
> > 
> > This RFC is for discussing how cache operation functions should be 
> > managed in the ARM tree.
> ...
> > The source code implementation for ARM cache ops would be:
> > 
> > - a header file declaring the ops as weak C functions for at least full 
> > cache flush, full cache invalidate, cache line flush and cache line 
> > invalidate;
> > 
> > - SoC-specific, cpu-specific, and isa-specific definitions for these 
> > functions, in the form of C files.
> > 
> > - a default implementation in a lib/ file.
> > 
> > The object files shall be linked in decreasing precedence order, i.e. 
> > SoC file first, then cpu file, then isa file, then lib last, so that for 
> > each cache op, the weak symbol mechanism uses the most specific one.
> > 
> > One possible organisation for files would be (switch to fixed size font)
> > 
> >          (isa)   (cpu)     SoC)
> > arch/arm
> >          /armv5t/
> >                  cache-ops.c
> >                  arm926ejs/
> >                            cache-ops.c
> >                            orion5x/
> >                                    cache-ops.c
> > 
> > Plus of course arch/arm/lib/cache-ops.c.
> 
> As a new-comer to the u-boot code, is there a difference between this
> implementation and say, a struct of function pointers?  eg the struct
> would default to armv5t ops, and arm926ejs init could redefine, say,

s/redefine/reassign/

> cache line invalidate.
> 
> The reason I ask is that I think the struct of function pointers would
> be easier for new folks to sort out with cscope, et al.  Whereas, the
> weak declarations with multiple implementations would muddy the waters
> when learning the code.
> 
> Am I missing something?  What are the advantages of weak declarations
> over redefined function pointers?
> 
> thx,
> 
> Jason.
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