vesafb mtrr setup question

[Arvind Sankar <arvinds@MIT.EDU>]

The following lines are pulled out of drivers/video/vesafb.c (2.4.20):
Line 646 onwards..

> if (mtrr) {
>         int temp_size = video_size;
>         /* Find the largest power-of-two */
>         while (temp_size & (temp_size - 1))
>                 temp_size &= (temp_size - 1);
>                 
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.

>         /* 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? If it fails
the first time round, shouldn't we either give up or attempt requesting
several contiguous segments?

-- arvind