From: Marcus Sundberg <mackan@stacken.kth.se>
  To  : ggi-develop@eskimo.com
  Date: Tue, 11 May 1999 07:26:07 +0000

Re: MMIO accel with kgicon drivers.

Jon M. Taylor wrote:
> 
> On Mon, 10 May 1999, =?iso-8859-1?Q?Jonas_Borgstr=F6m?= wrote:
> 
> > Hi, all
> >
> > I have recently tried XGGI, and it works great. I first tried the matroxfb
> > driver, it was fast but I didn't manage to get any resolution bigger than
> > 640x480. And after using fbset a while I had to reboot the computer.
> > After that I tried my old Matrox Millennium driver, and it worked in all
> > resolutions but, because it uses ioctrls to accelerate it is a lot slower
> > than the matroxfb driver that uses direct mmio accel.
> >
> > So, what should I do:
> >
> > Should I try to use the matroxfb and somehow get my resolution
> > (1024x768x16), but I like kgicon with and the generic monitor driver and
> > setmon.
> >
> > Or should I update my driver to use mmio acceleration?
>
>         MMIO acceleration is a security hole.

Not anymore than fbcon already is.

> What is really needed for a
> good solution to this problem is accel-operation FIFOs to reduce the
> number of kernel-user transitions, as this is what kills performance.
> Steffen's new KGI 0.9 design has exactly this, for exactly this reason.

The old Dali KGI had it too, but unfortunately there was only one
driver that used it... (the Mystique)
But in any case mapping the accel registers to userspace should
always be possible. For KGI 0.9 it probably will require root privs
(or my preference - a separate device which you can give whatever
permissions you want) and only be used for things requiring all the
speed they can get, and for the KGI 0.9 KGIcon wrapper it should be
available just like with native fbcon drivers.

//Marcus
-- 
-------------------------------+------------------------------------
        Marcus Sundberg        | http://www.stacken.kth.se/~mackan/
 Royal Institute of Technology |       Phone: +46 707 295404
       Stockholm, Sweden       |   E-Mail: mackan@stacken.kth.se