On Fri, Jan 09, 2015 at 10:55:51AM +0000, Arnd Bergmann wrote: > On Friday 09 January 2015 10:33:07 Catalin Marinas wrote: > > On Wed, Jan 07, 2015 at 07:48:48PM +0000, Arnd Bergmann wrote: > > > > In other cases that's actually a good thing. One such example is the > > > "Principles of ARM Memory Maps" document that tells hardware implementers > > > to do a rather complex mapping "To support 36-bit x86 PAE compatible operating > > > systems, such as Linux." but makes life much harder in the process than > > > any of the random mappings we have seen in the wild. > > > > Unfortunately, with any significant amount of RAM (say 16GB), this > > document becomes pretty useless. It basically forces you to have a very > > sparse physical address map from 0 to over 40-bit. I wouldn't apply the > > ARM memory maps doc to server systems. > > Are you sure? I was under the impression that this document was targetted > specifically at servers. Ah, sorry for the confusion, I haven't read the latest (apparently from 2012) update which covers 44 and 48-bit memory maps. The only downside is that for more than 32GB of RAM (up to 512GB) it requires a 40-bit memory map. Given the sparseness, we can't use 3-levels of page table with 4KB pages which can only cover 39-bit. Anyway, not a major issue. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
