On Thu, 6 Oct 2005, Martin Husemann wrote:
On Thu, Oct 06, 2005 at 01:39:10PM -0600, Marc Aurele La France wrote:
No. My preference is definitely to keep the OS out of the way, as much as
possible
Ok, but in this case that is not realy possible. You need a OS driver
that understands your mmap() call anyway to get the IOMMU mappings
correct & consistent.
We do not allow generic mmap'ing of PCI memory ranges, because that would
mean we had to try very hard to keep all OS drivers out of the way or
somehow synchronize the userland mapping with them.
On i386 with plain pass-through PCI access thinks are certainly different.
You're assuming the X server would indiscriminately trample all over such
mappings. That's not the case on SPARC any more than it is on x86.
I also don't see why this "is not really possible" with NetBSD, when it works
very well through Linux and SunOS (... and I _do_ mean "through").
The idea here is to support PCI, not PCI/x86, PCI/SPARC, ad nauseam. This
means creating a generic model of PCI and filtering out host differences
before presenting that model to our video drivers. The less lobotomies of
PCI the underlying OS implements, the better. The only restriction on PCI
this architecture actually implements is its default handling of master
aborts. And even that assertion is debatable. _All_ other restrictions are
necessarily OS inventions.
No matter how you look at it, some NetBSD kernel work will be required for
multihead to work on both uni-domain (Sabre & Hummingbird) and multi-domain
(Psycho, Schizo & Tomatillo) systems.
The first thing to look at is PCI I/O. I see from the logs posted on this
thread that the kernel clobbers OBP's assignment of PCI I/O BARs. This
clobbering needs to be removed. There also needs to be an ability to map in
one chunk the entirety of a host bridge's PCI I/O range. Doing this mapping
per device isn't practical because PCI limits assignments to 256 bytes (which
is less than the host page size) and per-device mappings don't allow for
unregistered assignments such as those for VGA, 8514/A, etc.
It doesn't really matter whether PCI memory mappings are done per-device,
per-domain, or through some more liberal /dev/mem clone. The caveat here is
that should you require that such mappings be done per-device, you had
better ensure even PCI ROM pointers are assigned, valid and mappable.
Marc.
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