On Fri, 30 May 2014, Rob Herring wrote: > There's work in flight to support early_ioremap, early console, and RO > text patching which all use the fixmap region. > > There's a couple of options to solve this: > > - Only support up to 16 cpus. It could be anywhere between 17-31, but > that seems somewhat unlikely. Are we really ever going to see 32-bit > 32 core systems?
I wouldn't rule that out. I've seen 16-core ARM chips in 2008 (although they didn't go into production). Silly limitations like that always come back to bite you. And we have better alternatives. > - Reduce KM_TYPE_NR from 16 to 15. Based on the comment for it, we > probably don't want to do that. Is increasing it to the default of 20 > worthwhile? Some of the options here would allow doing that. > - Add 0xffe00000-0xfff00000 to the fixmap region. This would make > fixmap span 2 PMDs with the top PMD having a mixture of uses like we > had before. That would be my preferred approach. Note here it could be 0xffe00000-0xfffe0000 to include the whole of the previous fixmap area curently unused. > - push the PCI i/o space down to 0xfec00000 and make fixmap 4MB. This > is a cleaner solution as the 2 PMDs are only used for fixmap. This may > require some static mapping adjustments on some platforms. No need. With the latest changes, the fixmap area is between 0xffc00000 and 0xffe00000 (there is apparently a mistake in Documentation/arm/memory.txt). So currently 0xff000000-0xffc00000 is free, which makes the fixmap area far away from the PCI i/o area with plenti of space in between. > - Same as previous option, but convert the PCI i/o space to fixmap > entries. We don't really need all 2MB for PCI. See above. > Also, there is an error in the documentation below: > > > > > Signed-off-by: Liu Hua <[email protected]> > > --- > > Documentation/arm/memory.txt | 2 +- Yep, good that you spotted it as well. I failed to catch it during my review so I'll send a patch. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
