Messages in this thread | | | From | "Luis R. Rodriguez" <> | Date | Tue, 29 Mar 2016 17:34:08 -0700 | Subject | Re: [PATCH 2/2] x86/mtrr: Refactor PAT initialization code |
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On Tue, Mar 29, 2016 at 6:07 PM, Toshi Kani <toshi.kani@hpe.com> wrote: > On Tue, 2016-03-29 at 16:43 -0700, Luis R. Rodriguez wrote: >> I meant to ask about the case where the option the lets a user go in a >> muck with BIOS settings to disable MTRR e xists and the user disables >> MTRR. What would happen for fan control in such situations? I'd >> imagine such cases allow for a system to exist with proper fan >> control, and allow the kernel to boot without having to deal with the >> pesky MTRRs at all, while PAT lives on, no? > > You mean user disables MTRRs from BIOS setup menu?
Yup!
> I am not a BIOS guy, > but I do not think it offers such option when the code depends on it...
Darn, I'm pretty sure I've seen such option before... can't seem to find such a toggle now.
>> When you say regular memory you mean everything else we see as RAM? I >> was under the impression we'd only need MTRR for a special range of >> memory, and its up to implementation how they are used. If you can use >> MTRR to change the cache attribute for regular RAM and if this is >> actually a requirement if the default MTRR is UC then one way or >> another a BIOS seems to always require MTRR, either for UC setting for >> fan control or WB for regular RAM, is that right? > > Right, in one way or the other, MTRRs set WB to RAM and UC to MMIO. PAT is > overwritten by MTRRs, so RAM must be set to WB.
I see... thanks....
Luis
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