[OpenBIOS] OpenBIOS and ppc64?

[Alexander Graf]

On 01.10.2010, at 00:28, Benjamin Herrenschmidt wrote:

> On Fri, 2010-10-01 at 00:25 +0200, Alexander Graf wrote:
>> On 01.10.2010, at 00:09, Benjamin Herrenschmidt wrote:
>> 
>>> On Fri, 2010-10-01 at 00:03 +0200, Alexander Graf wrote:
>>> 
>>>> If I understand the U3 and U4 designs correctly, PCI is always bound
>>>> to be within the first 32 bits. Copying Ben for verification. I don't
>>>> really remember having seen 64 bit cells on any Power system either,
>>>> but I could be wrong. Again, let's ask the expert here :).
>>> 
>>> Yes. However, on js2x, the firmware plays funny remapping tricks...
>>> 
>>> In general, however, OpenBIOS should be fixed. It's getting more common
>>> to have even 32-bit machines with physical devices above 32-bit (even
>>> ARM is now growing an equivalent of PAE for that, and almost all 4xx
>>> powerpc do that).
>> 
>> So how does the firmware tell the OS that a device is on a 64 bit physical
>> address if it only knows about 32 bit wide cells?
> 
> #address-cells & #size-cells indicate the number of cells for an address
> or a size :-)

Ah - that makes sense. So I guess cell size really does stay 32 bit on POWER. Very good :).

> 
>>> 
>>>>> What's the plan for fixing this? Will we need an openbios-ppc64
>>>> after all, or is there a way to fix these issues in openbios-ppc using
>>>> uint64_t and some assembler magic? The 970 init
>>>> (arch/ppc/qemu/init.c:ppc64_patch_handlers) apparently does something
>>>> clever for the interrupt handlers and seems able to use 64-bit ld/std
>>>> instructions in start.S. That still wouldn't help with ucell based
>>>> structs and C functions of course...
>>>> 
>>>> Those are pure fixups to get back to 32 bit mode from the interrupt
>>>> handlers, as they go into 64 bit mode by default.
>>> 
>>> OpenBIOS should be generally fixed regardless of being 32 or 64-bit for
>>> being capable of handling 64-bit physical addresses. As to accessing
>>> those from 32-bit mode, for that I suppose it either
>>> 
>>> - runs in virtual mode exclusively on such machines so it can create
>>> special mappings in the MMU (4xx)
>>> 
>>> - use a little asm stub that switch mode & back on real 64-bit machines
>>> to access locations in the 64-bit address space
>>> 
>>> I'm no fan of the later due to the "issues" with doing I/Os in real mode
>>> on many powerpc chips but that's how IBM own firmware works so ..
>> 
>> Actually we should be able to do the former even for 64-bit Book3S systems.
>> After all, we run in virtual mode always and own the HTAB. And that contains 64 bit addresses.
> 
> Apple OF runs in virtual mode. IBM in real. Dunno if AIX can cope with
> virt.

Phew. What does SLOF run in? Btw - that'd be the alternative: emulate a U4 board and have SLOF run inside.


Alex