On Sat, 2013-06-29 at 13:37 +0200, Paul Menzel wrote:
Dear coreboot folks,
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Searching the code for that Kconfig variable, I get the following results
$ git grep MMCONF_SUPPORT_DEFAULT src/Kconfig:config MMCONF_SUPPORT_DEFAULT src/arch/x86/include/arch/io.h:#if CONFIG_MMCONF_SUPPORT_DEFAULT src/arch/x86/include/arch/io.h:#if CONFIG_MMCONF_SUPPORT_DEFAULT
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and I wonder why this option is not selected for more platforms or even enabled by default (for systems having `MMCONF_SUPPORT`)? Reading the AMD whitepaper it claims that the Linux kernel can determine if MMIO is there during runtime [3]. Though I have no idea if that is only possible because of the firmware setting things up correctly beforehand.
Additionally for Intel systems `MMCONF_SUPPORT` (without `_DEFAULT`) seems to be selected in each mainboard where for AMD systems it is done under `src/cpu`.
To use MMCONF_SUPPORT_DEFAULT you need to enable MMCONF as one of the very first things you do.
For Intel see haswell/bootblock.c or gm45/early_init.c. Both use explicit PCI IO style config access to do the job. This explicit early write is missing on some other chipsets, thus you cannot blindly enable MMCONF_SUPPORT_DEFAULT. There is no hardware restriction AFAIK, patches welcome.
For AMD the same enable function is in cpu/amd/car/cache_as_ram.inc. One really should not be using PCI IO configs on AMD multiprocessor platforms, please submit patch to select MMCONF_SUPPORT_DEFAULT for any AMD board with MMCONF_SUPPORT.
IMHO, MMCONF_SUPPORT and MMCONF_SUPPORT_DEFAULT belong under northbridge/ while MMCONF_BASE_ADDRESS belongs under mainboard/.
Kyösti