Messages in this thread | | | Date | Fri, 21 Sep 2007 17:27:17 -0700 | From | "Siddha, Suresh B" <> | Subject | Re: MTRR initialization |
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On Fri, Sep 14, 2007 at 09:33:30AM -0700, Howard Chu wrote: > Hi, was wondering if anyone else has been tripped up by this... I've got > 4GB of > RAM in my Asus A8V Deluxe and memory hole mapping enabled in the BIOS. By > default, my system boots up with these MTRR settings: > > reg00: base=0x00000000 ( 0MB), size=4096MB: write-back, count=1 > reg01: base=0x100000000 (4096MB), size=1024MB: write-back, count=1 > reg02: base=0xc0000000 (3072MB), size=1024MB: uncachable, count=1 > reg03: base=0xc0000000 (3072MB), size= 256MB: write-combining, count=1 > > The X server and various other programs try to add a mapping for my video > card's buffer, at 0xd0000000, size=256MB, type=write-combining, and this > always > fails with a type mismatch error (old type is write-back). Apparently it's > conflicting with mapping register 0. I can't just disable the existing > settings > and re-add them; the system hangs soon after disabling reg01. > > I guess the kernel must be getting the initial setup from the BIOS. I've > hacked > around this in mtrr/generic.c by explicitly changing the MTRR state in > get_mtrr_state to split the first mapping into two; one at base 0 size > 2048M > and one at base 2048M size 1024M. So now I have this, which is pretty much > what > I wanted: > > reg00: base=0x00000000 ( 0MB), size=2048MB: write-back, count=1 > reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1 > reg02: base=0x100000000 (4096MB), size=1024MB: write-back, count=1 > reg03: base=0xc0000000 (3072MB), size=1024MB: uncachable, count=1 > reg04: base=0xc0000000 (3072MB), size= 256MB: write-combining, count=1 > reg05: base=0xd0000000 (3328MB), size= 256MB: write-combining, count=1
BTW, having overlapping WC, UC regions make the end result UC. So in this case, you may not be getting the desired performance.
> > So the question is - was there an easier/correct way to do this? > > It might have been nice if the MTRR ioctls allowed the register number to > be > specified on the Set commands, though I'm not sure that would have helped > in > this case. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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