Re: Claim on IEEE1275

[Marco Gerards]

Hollis Blanchard <address@hidden> writes:

> On Dec 28, 2004, at 5:02 PM, Marco Gerards wrote:
>>
>> Some minutes ago I have committed a patch that removes the stack
>> initialization code.  This seems to work perfectly fine for both the
>> PegasosII and the newworld mac.  This was required for loading linux
>> on the PegasosII.  Without this change linux crashed when decompressing
>> itself.  It's ok for me to restore this code when the problem is
>> found.  But at the moment this seems like a fine fix.
>
> I would still like to have some idea of the problem we're avoiding. We
> *were* using an 8KB stack (which seems like a lot). Now we use
> whatever firmware gave us. Firmware is required by spec (8.2.2 of the
> PowerPC IEEE1275 binding) to give us at least a 32KB stack, but of
> course we cannot guarantee that all implementations do this
> correctly. It is possible that Linux's gunzip code requires a stack
> greater than 8KB, and that would be good to know (and comment). Would
> you mind testing the old code with larger stack sizes and see if that
> matters?

I've done that before I removed it.  It did not help.  Perhaps the
problem is caused because stack is in .bss and it is not executable?

> I said earlier that I didn't think the old stack initialization code
> was correct, but now I think it may be ok. I have never seen use of
> the "la" mnemonic, but it might do what we want here.

Ok.  Hopefully Johan can comment on that, he wrote that code.

>> Only one problem remains for loading linux on the PegasosII.  The
>> grub_claimmap call fails because the map fails.  I think this is
>> because the firmware already maps the memory.
>
> You can verify this by consulting the "translations" property of
> /chosen/mmu if I recall correctly.

Ok.

>> Hollis, is the map call really required?  We can better go back to
>> using grub_ieee1275_claim if it is not.  If it is required, do you
>> have an idea of how to detect this?
>
> It is certainly required: how would you like it if you claimed some
> memory to write to but it was never mapped?

I assume it is mapped by claim.  Anyway, yaboot does not use map and
neither does linux, as it seems.

> There is a "real-mode?" configuration variable, but I think that just
> specifies OF's translation mode, independent of the client's mode (see
> the IEEE1275 PowerPC and CHRP bindings). Knowing the value of that
> variable might be interesting but I wouldn't recommend changing it, as
> Apple firmware in particular is known to die a horrible death by
> mucking with one of those settings (I'm pretty sure it's "real-mode?").

On my powerbook it is set to false, while it is set to true on the
pegasos.  So what do you suggest?  Using map when it is set to false?

Thanks,
Marco