sparse and DRM on non-x86

[Jon Smirl]

On Fri, 01 Oct 2004 18:05:29 +0100, Keith Whitwell
<keith at tungstengraphics.com> wrote:
> > Second the DRM code always treats the framebuffer as if it is in
> > IOMEM. But what about IGP type devices where the framebuffer is in
> > main memory? These only exist on the x86 so treating their framebuffer
> > as IOMEM works since there is no difference between IOMEM and normal
> > memory access on an x86.
> 
> The framebuffer lives in agp memory on those devices, presumably this is iomem
> as it appears to be memory of the agp device.

On normal AGP/PCI cards the memory is on the card. It is accessed over
the AGP/PCI bus which requires special IO instructions on non-x86
hardware. IGP cards use the normal system memory for their buffers.
You don't use the special IO instructions to access this memory. The
key is where the memory lives, on the graphics card or on the
motherboard.

On x86 both types of memory use the same access instructions since the
x86 makes AGP/PCI memory look like normal system memory. So we don't
have a problem.

On other platforms introduction of an IGP type device will break
X/mesa since they don't know to switch from IO instruction access to
normal memory access. IA64 may have already run into this on
unreleased products since they have been asking questions along these
lines.

-- 
Jon Smirl
jonsmirl at gmail.com