[coreboot] [PATCH] AMD MMCONF Support

[Myles Watson]

>> Arne:
>> Could you help me understand MMCONF_SUPPORT and
>> MMCONF_SUPPORT_DEFAULT?  It looks like the area gets reserved for
>> MMCONF_SUPPORT, even if MMCONF_SUPPORT_DEFAULT isn't selected.
>
> My understanding of the code as it was before I started messing with it,
> is that MMCONF_SUPPORT is intended to indicate whether the facility is
> available at all, and MMCONF_SUPPORT_DEFAULT toggles the actual use of
> it (by Coreboot).  Both src/northbridge/amd/amdfam10/northbridge.c and
> src/northbridge/intel/i945/northbridge.c contains code like this:
>
>  #if CONFIG_MMCONF_SUPPORT_DEFAULT
>          .ops_pci_bus      = &pci_ops_mmconf,
>  #else
>          .ops_pci_bus      = &pci_cf8_conf1,
>  #endif
>
> which, alongside romcc_io.h's
>
>  #if CONFIG_MMCONF_SUPPORT_DEFAULT
>          return pci_mmio_read_config32(dev, where);
>  #else
>          return pci_io_read_config32(dev, where);
>  #endif
>
> is more or less the only use for MMCONF_SUPPORT_DEFAULT as far as I can
> see.  I'll leave it to others to determine if this actually makes sense.
>
> (Having SUPPORT without SUPPORT_DEFAULT gives you an MCFG area that you
> can communicate to the OS (at least potentially), as well as the option
> of explicitly doing individual config accesses via mmio instead of
> ports.  I don't think anyone is doing either of these today.)

Thanks for the explanation.  It looks like the trouble with reserving
a region for MMCONF is related to broken UMA code.

Thanks,
Myles