Re: better leve triggered IRQ management needed

["linux-os \(Dick Johnson\)" <linux-os@analogic.com>]

On Mon, 24 Apr 2006, Linus Torvalds wrote:

>
>
> On Mon, 24 Apr 2006, Stephen Hemminger wrote:
>>
>> We should fail request_irq() if the SA_SHIRQ but the irq is edge-triggered.
>
> That would be HORRIBLE.
>
> Edge-triggered works perfectly fine for SA_SHIRQ, as long as there is just
> one user and the driver is properly written. Making request_irq() fail
   ^^^^^^^^_______ Must be a trick!
> would break existing and working setups.
>

If there is just one user then it isn't shared! Get real.

> If you have a driver that requires level-triggered interrupts, then your
> driver is arguably buggy. NAPI or no NAPI, doesn't matter. Edge-triggered
> interrupts is a fact of life, and deciding that you don't like them is not
> an excuse for saying "they should not work".
>

It's trivial to write a driver where the ISR completely handles the
interrupt so that another edge can happen. It is impossible to write
a driver that shares such an edge-driven interrupt with another.

> You can get an edge by having your driver make sure that it clears the
> interrupt source at some point where it requires an edge.
>
> And yes, that may mean that when you're ready to start taking interrupts
> again, you are required to first read all pending packets, instead of just
> assuming that a level-triggered interrupt will "just happen", but that's
> the harsh reality for writing a driver that actually WORKS.
>
> For a driver writer, there is one rule above _all_ other rules:
>
> 	"Reality sucks, deal with it"
>
> That rule is inviolate, and no amount of "I wish", and "it _should_ work
> this way" or "..but the documentation says" matters at all.
>
> If you can't take that rule, don't write drivers, and don't design
> infrastructure for them.
>
> 		Linus

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.4 on an i686 machine (5592.89 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_
\x1a\x04

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