Messages in this thread | | | Date | Tue, 10 Jun 2014 14:52:32 +0800 | From | Liu hua <> | Subject | Re: [PATCH v3 2/2] ARM : change fixmap mapping region to support 32 CPUs |
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On 2014/5/31 3:25, Nicolas Pitre Wrote: > 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.New
Now our team is woring on arma15 with 16 CPUs. > >> - 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 <sdu.liu@huawei.com> >>> --- >>> 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. >
Very sorry for the mistake and ignoreing this mail. Maybe I should imporve my email client!
Thanks again for Nicolas.
Thanks, Liu Hua > > Nicolas > > . >
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