On Fri, Apr 27, 2007 at 04:04:25PM -0700, Andrew Morton wrote:
It's not a closed vs. open issue, it just turns out that a lot of people
keep trying to write PCI drivers in userspace (how many different papers
were published on this topic alone in the past year...). This framework
is to allow this to happen in a sane and correct way.
Lots of different types of odd devices do not fit into the "kernelspace
driver" framework very well for a variety of reasons:
- zillions of different controls in the card
- floating point is needed to compute the next step of an
operation in moving a physical object
With this framework, we provide a solid and simple way to provide for
these kinds of devices. The Linutronix guys have had a lot of
experience in supporting this kind of hardware in the past and can
provide better examples if you need.
But yes, it does allow you to write a PCI driver in userspace, being
closed source, if you really want to. But if you do that, then you get
_no_ advantages of being in the kernel (caching, common userspace
interface, resource management, etc.) and need to handle that all
yourself. Heck, that's pretty much what X does today for lots of old
video cards :)
No, you still need kernel code to handle the interrupt properly, we do
not want userspace to do this as it would slow the system down and do
all sorts of other bad things. That's the main problem with all of
those other proposals that people have for trying to do this kind of
work in the past (can't share irqs, can't block on userspace in an
interrupt handler, etc.)
thanks,
greg k-h
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