[coreboot] [PATCH] AMD MMCONF Support
Myles Watson
mylesgw at gmail.com
Mon Sep 13 18:44:40 CEST 2010
>> 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
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