On Tue, 2002-06-18 at 10:57, Keith Whitwell wrote:
>
> > - IOIO and IOMEM access
> >
> > iopl() gives access to IOIO
> > mmap() and AGP driver gives access to IOMEM/AGP
> >
> > IOIO is actualy slightly slower in CPL3 than in CPL0, but it's
> > slower in CPU cycles, not in IO cycles. And since IO cycles
> > definitely dominate in IOIO (by orders of magnitude), this isn't
> > likely to be an issue.
> >
> > And IOMEM is the same speed, since the only overhead for
> > user space is the TLB, and AGP mappings use the TLB even in kernel
> > space (vmalloc).
>
> I'm not sure how this works. Does the agp module have a facility to allow the
> client to mmap the card mmio region & the framebuffer? I wasn't aware of this.
I don't know about that, but framebuffer devices certainly do. Not sure
if they will after the ongoing API changes in 2.5 though.
And failing that, one could fall back to /dev/mem, like DGA clients. Not
that I advocate that. :)
Just two cents of mine...
--
Earthling Michel Dänzer (MrCooper)/ Debian GNU/Linux (powerpc) developer
XFree86 and DRI project member / CS student, Free Software enthusiast
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