Messages in this thread | | | Date | Mon, 19 Oct 2009 16:59:57 +0200 | From | Thomas Schlichter <> | Subject | Re: [RFC Patch] use MTRR for write combining if PAT is not available |
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Suresh Siddha wrote: > If we are going to make ioremap() and set_memory_wc() add mtrr's in > non-pat case, then we need to delete the added mtrr(s) in the > corresponding iounmap() and set_memory_wb() aswell. > > hmm, this is becoming too complex. The way i915 and other graphics > drivers are using set_memory_wc(), it is def a bad idea to start adding > mtrr's behind the back for non-pat case.
Yes, maybe it's better to drop it for ioremap() and set_memory_wc(). But I'd like to keep it for mmapping the PCI region. It should help all the people with PAT-incapable CPUs and graphics chips without DRM support (for them there simply is no driver that should set up the MTRR entries...).
> Can't we just force PAT option always and we probably don't care about > ioremap_wc() on processors were PAT doesn't get enabled because of known > errata.
I don't think this is a good idea, Robert Hancock wrote there may be millions of such Laptops (Core Solo/Duo erratum AE7, Pentium M erratum Y31) : http://marc.info/?l=linux-kernel&m=125537136105246&w=2
> or Perhaps just try to add mtrr only for the pci mmap case like the 4th > patch in this series..
I'd prefer this! ;-)
Kind regards, Thomas
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