linux-kernel - Re: Simulating level triggered interrupts with edges

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Message-ID: <alpine.LFD.2.02.1106222233580.11814@ionos>
Date:	Wed, 22 Jun 2011 23:32:03 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: Simulating level triggered interrupts with edges

On Wed, 22 Jun 2011, Mark Brown wrote:

> I've run into a couple of cases recently where a system has had a device
> with a level triggered interrupt connected to an edge triggered
> interrupt controller.  Ignoring for the minute the hardware design
> concerns one might have this strikes me as something I'd expect the
> kernel to take a reasonable stab at handling in common code since it
> should be possible to have the core simply call the level triggered
> handler repeatedly until it returns IRQ_NONE when used with an edge
> based interrupt.  Obviously this leaves something to be desired but
> something like this seems to be the most sensible way to deal with such
> systems.
> 
> Is this supported by the current code?  I can't see any such support but
> that doesn't mean I'm not missing it.  If it is not supported and I'm
> not missing some much bigger problem with the idea can you make any
> suggestions about the least bad way to allow systems to do this?

No, we don't have support for this. Drivers should be careful about
such issues, but yes I can understand that we should think about
having support in the core code for such HW crap instead of cluttering
the drivers with such issues.

Though it's non-trivial. Think threaded interrupts, where we cannot
deal with that in handle_irq_edge(). I have no immediate idea how to
solve that at the core code, but feel free to have a stab.

Thanks,

	tglx



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