Kernel configuration options

Bernardo Innocenti bernie at laptop.org
Wed Jan 2 08:18:21 EST 2008


Tom Sylla wrote:

> http://openbios.org/viewvc/cpu/x86/pc/olpc/lxmsrs.fth?view=markup&revision=739&root=OpenFirmware
> has:
>   msr: 0000.1810 fdfff000.fd000111.  \ Video (write through), fbsize
> 
> which is setting the framebuffer as write-combining. (the "write
> through" comment is incorrect)

This takes care of the physical mapping, but how would userspace
be able to mmap the framebuffer into virtual memory without
additional MMU programming?

I was under the impression that we also need to cover the whole
region with small 4KB MMU pages.  This degrades performance
somewhat due to TLB misses when the CPU accesses the framebuffer.

But I must confess I have limited understanding of the Geode
architecture, so I may be overlooking something.

-- 
 \___/
 |___|   Bernardo Innocenti - http://www.codewiz.org/
  \___\  One Laptop Per Child - http://www.laptop.org/


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