Re: User mode drivers: part 1, interrupt handling (patch for 2.6.11)

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Date:	Mon, 14 Mar 2005 22:15:36 -0500
To: Alan Cox <alan@lxorguk.ukuu.org.uk>

On Mon, 14 Mar 2005 13:33:31 +0000, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> On Llu, 2005-03-14 at 00:02, Peter Chubb wrote:
> > I can see there'd be problems if the code allowed shared interrupts,
> > but it doesn't.
>
> If you don't allow shared IRQ's its useless, if you do allow shared
> IRQ's it deadlocks. Take your pick 8)
>
> As to your comment about needing to do a few more I/O operations I
> agree. However if your need is for speed then you might want to just
> write a small IRQ helper module for the kernel or extend the syntax I
> proposed a little (its conveniently trivial to generate native code from
> this).

The concept of passing in a little structure telling how to
acknowledge an interrupt is a very good one. I'd like to see it added
as a kernel feature so that drivers could start being converted to it.
This is a big deal for Xen since Xen has the same problem with
forwarded IRQs. Xen would pass the little structure from the domain to
the supervisor so that the supervisor could cut off the IRQ if the
domain fails.

>
> There isn't much you can do about the status read without MWI on most
> chip designs (some get it right by posting status to system memory but
> not many)
>
> Alan
>
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-- 
Jon Smirl
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