[OpenBIOS] OpenBIOS and ppc64?

[Alexander Graf]

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?

> 
>>> 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.


Alex