Re: vesafb mtrr setup question

[Alan Cox]

On Llu, 2003-08-25 at 20:43, Arvind Sankar wrote:
> In the first place, the power of two computation computes the largest
> power of 2 that is _smaller_ than video_size, so it looks like an
> off-by-1 bug.

Not a bug - we don't know what lives above it so we can't extend the
mtrr safely

> >         /* Try and find a power of two to add */
> >         while (temp_size && mtrr_add(video_base, temp_size, MTRR_TYPE_WRCOMB, 1)==-EINVAL) {
> >                 temp_size >>= 1;
> >         }
> > }
> 
> Secondly, what's the point of requesting a smaller write-combining
> segment that won't cover all the video memory being used?

Generally we don't use all the videoram. Its a heuristic rather than
perfection. You might want to play with improvements

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