[U-Boot-Users] [PATCH] Make MPC83xx one step closer to full relocation.

[Joakim Tjernlund <Joakim.Tjernlund@transmode.se>]

> -----Original Message-----
> From: u-boot-users-bounces at lists.sourceforge.net [mailto:u-boot-users-bounces at lists.sourceforge.net]
> On Behalf Of Stefan Roese
> Sent: den 8 april 2008 21:53
> To: joakim.tjernlund at transmode.se
> Cc: u-boot-users at lists.sourceforge.net; 'Kim Phillips'; Wolfgang Denk
> Subject: Re: [U-Boot-Users] [PATCH] Make MPC83xx one step closer to full relocation.
> 
> On Tuesday 08 April 2008, Joakim Tjernlund wrote:
> > > On 4xx execution always starts at 0xfffffffc (last lword in 32bit address
> > > space). This location holds a jump to _start for 405 PPC's and to
> > > _start_440 for 440 PPC's. 440 PPC's need some extended initialization
> > > (TLB setup etc) and later jump to the 4xx common _start.
> >
> > OK, then it is like I suspected. What if you rename _start to
> > _common_start. Make _start equal _common_start for 405 and rename
> > _start_440 to _start, i.e make sure that _start is defined where you
> > start executing after the jump.
> 
> As I mentioned earlier, _start_440 is mapped to 0xfffff000 via the linker
> script since the jump from 0xfffffffc can't be too long (because of the 4k
> shadow TLB entry). So renaming _start_440 to _start won't help here. It can
> be done, but frankly I don't have the time for it currently.

I see, suspected that we would not get away that easy :(

> 
> > > I'm an linker script dyslexic. So no idea if we can handle this solely in
> > > the linker script or if we need a new common symbol in the PPC start.S's.
> >
> > Both ways should be doable I think. A linker script would probably look
> > something like(pseudo diff below):
> >  .text      :
> >   {
> > +    _monitor_base = . ;
> > +    PROVIDE (_monitor_base = .);
> >     cpu/mpc83xx/start.o	(.text)
> >
> > And then add a
> > 	GOT_ENTRY(_monitor_base)
> > in start.S
> 
> The disadvantage I see is that I need to change the linker scripts for all
> boards for such a solution. Doesn't sound like fun.

Yeah, probably easier to define the symbol in start.S and skip the linker
version. 

> 
> So for now, I would really like to see the old version with the ugly
> CFG_MONITOR_BASE back so that 4xx board can be used again.

Then I would ask you to do an #ifdef for ppc440(or similar). If the
long term solution should be to move _start to its true start vector, you
could just go back to the old way for ppc4xx. If the long term solution should
be a new symbol you could just impl. that for ppc4xx and just use it for
ppc4xx only, then the other archs can follow when the next merge window opens.

    Jocke
> 
> Best regards,
> Stefan