Subject: Re: Setting MTRRs from the X server
To: None <,>
From: Frank van der Linden <>
List: tech-kern
Date: 03/07/1999 11:46:00
On Sun, Mar 07, 1999 at 08:56:23AM +0100, Matthieu Herrb wrote:
> [David Dawes, from the XFree86 Project, asked me to foward this to the
> appropriate NetBSD Mailing list, please try to include him
> ( in the followups -- Matthieu]
> For XFree86 4.0, we really need to be able to have the X server request
> specific MTRR settings for different parts of a video card's physical
> memory address space.  While turning WC on for the framebuffer is a big
> performance boost, a more critical issue is being able to make sure that
> WC is turned off for areas that are used for memory mapped I/O.  We've
> found that some BIOSs enable WC in areas that our drivers want to use
> for MMIO.  One example is the 0xb0000-0xbffff range.

We currently do not have such an interface in NetBSD. It is not hard
to add, the mtrr code itself is small, and you just need to create
an interface for it, either an i386 specific system call or a kind
of "cpuctl" device.

However, I don't think anybody is doing this at the moment, so I don't think
we'll have this in the next release, unfortunately. If anyone wants to
do such a thing, get in touch with me, though.

- Frank