Re: vesafb-fix-mtrr-bugs.patch added to -mm tree

[Antonino A. Daplas]

Andrew Morton wrote:
> Dave Jones <davej@xxxxxxxxxx> wrote:
> > On Fri, Jul 29, 2005 at 11:24:37AM -0700, Andrew Morton wrote:
> >
> >  > From: "Antonino A. Daplas" <adaplas@xxxxxxxxx>
> >  > 
> >  > >> vesafb: mode is 800x600x16, linelength=1600, pages=16
> >  > >> vesafb: scrolling: redraw
> >  > >> vesafb: Truecolor: size=0:5:6:5, shift=0:11:5:0
> >  > >> mtrr: type mismatch for fc000000,1000000 old: write-back new: write-
> >  > >> combining
> >  > 
> >  > Range is already set to write-back, vesafb attempts to add a write-combining
> >  > mtrr (default for vesafb).
> >  > 
> >  > >> mtrr: size and base must be multiples of 4 kiB
> >  > 
> >  > This is a bug, vesafb attempts to add a size < PAGE_SIZE triggering
> >  > the messages below.
> >
> > I fixed this a few weeks back. It's this line which your patch removes..
> >
> > -        while (temp_size > PAGE_SIZE &&
> >
> >  > To eliminate the warning messages, you can add the option mtrr:2 to add a
> >  > write-back mtrr for vesafb.  Or just use nomtrr option.
> >
> > If we need users to pass extra command line args to make warnings go
> > away, we may as well not bother. Because 99% of users will be completely
> > unaware that option even exists.  They'll still see the same message,
> > and still report the same bugs.
> >
> > The pains of MTRR strike again. This stuff is just screaming for
> > a usable PAT implementation. Andi, you were working on that, any news ?
> > Or should I resurrect Terrence's patch again ?
>
> Well something is still awry:
>
>
>
>
> Begin forwarded message:
>
> Date: Fri, 29 Jul 2005 13:40:05 +0200
> From: Alessandro <alezzandro@xxxxxxxxx>
> To: Andrew Morton <akpm@xxxxxxxx>
> Subject: Re: "mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining" on Kernel 2.6.12
>
>
> I try the new prepatch for the stable Linux kernel (2.6.13-rc4) but
> the problem is the same:
> ...
> vesafb: framebuffer at 0xe0000000, mapped to 0xe0880000, using 4608k,
> total 131072k
> vesafb: mode is 1024x768x24, linelength=3072, pages=55
> vesafb: protected mode interface info at c000:56cb
> vesafb: scrolling: redraw
> vesafb: Truecolor: size=0:8:8:8, shift=0:16:8:0
> mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,4000000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,2000000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,1000000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,800000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,400000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,200000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,100000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,80000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,40000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,20000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,10000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,8000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,4000 old: write-back new: write-combining
> mtrr: type mismatch for e0000000,2000 old: write-back new: write-combining

Vesafb defaults to write-combining mtrr.  But the memory range is already
set to write-back so mtrr_check() spewed the above messages. I don't think it
has any ill effects, but if you want to eliminate the above messages, tell
vesafb to also use write-back mtrr by adding the boot option "mtrr:2"
(or nomtrr).

I think I'll submit a documentation patch.

Tony
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