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Re: user-level drivers

From: olafBuddenhagen
Subject: Re: user-level drivers
Date: Tue, 15 Nov 2011 01:33:33 +0100
User-agent: Mutt/1.5.21 (2010-09-15)


On Tue, Nov 15, 2011 at 12:02:58AM +0100, Samuel Thibault wrote:

> Considering the target of user-level drivers, I've come to a few
> biting points:
> - we should have a PCI arbitrer in the end. - that arbitrer should
> permit to confine drivers to resources of only one PCI device, no more
> (though of course with DMA, without IO-MMU, you could access anywhere
> on the machine, but that's way less probable, and still the arbitrer
> might be able to govern them).

Yes, that's what I had in mind all along: a bus driver that presents a
node for each attached device, giving the driver using this node access
to exactly the resources it needs for the device in question.

However, I don't expect that to be implemented any time soon...

> - so the user-level interface we are discussing at the moment will
> probably just be replaced at that moment.

I'm not sure it will change all that much?

> - so do we really need to polish it yet more, or else simply start
> using it, and see what's broken in it?

Well, depends what you mean exactly. The physical memory allocation
interface in the original branch is just wrong, and clearly not
acceptable for mainline IMHO.

As for the interrupt stuff, we discussed a number of variants, and I'm
not sure which one is best. I think I liked your proposal most
(reenabling IRQ on reply to the notification message); but I guess I
wouldn't mind sticking with the currently implemented interface
either... (Although it is clear that it *will* have to change when
implementing a bus driver -- while your variant should be fine in that
case as well I think.)


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