Re: PAT support

[David Young <dyoung%pobox.com@localhost>]

On Thu, May 20, 2010 at 07:54:46AM +0200, Christoph Egger wrote:
> The combined effect of MTRR and PAT memory types:
> 
> PAT memory type  MTRR memory type    effective memory type
> UC               UC, WC, WP, WT, WB  UC
> UC-              UC                  UC
> UC-              WC                  WC
> UC-              WP, WT, WB          UC
> WC               â                   WC
> WP               UC                  UC
> WP               WC                  UC
> WP               WP                  WP
> WP               WT                  UC
> WP               WB                  WP
> WT               UC                  UC
> WT               WC, WP              UC
> WT               WT, WB              WT
> WB               UC                  UC
> WB               WC                  WC
> WB               WP                  WP
> WB               WT                  WT
> WB               WB                  WB

ISTM that the effective memory type (EMT), not the PAT memory type,
should be controlled by pmap(9).  MTRR and PAT should be consistent, and
no single physical page should be mapped once with one EMT and a second
time with an inconsistent EMT.

> On 20.05.10 01:15, David Young wrote:
> > Are some memory types more suitable for a DMA buffer than others?
> 
> For MMIO you can use either Uncachable, Uncacheable Minus or Write-Combine.

Ok.  What about DMA buffers?

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 278-3933