linux-kernel - Re: [PATCH 1/3] clocksource: atmel-st: Remove irq handler when clock event is unused

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Date:	Mon, 3 Aug 2015 16:36:29 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Dueck <davidcdueck@...glemail.com>,
	Sebastian Sewior <bigeasy@...utronix.de>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 1/3] clocksource: atmel-st: Remove irq handler when clock
 event is unused

On Mon, 3 Aug 2015, Boris Brezillon wrote:
> On Sun, 2 Aug 2015 11:40:28 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Sun, Aug 02, 2015 at 11:10:21AM +0200, Thomas Gleixner wrote:
> > > I think Boris Brezillon had implemented it at some point, but it was
> > > shot down for reasons I can't remember. 
> > 
> > You weren't around at the time.. DT people didn't like it, said they
> > didn't like having to make up fake hardware in their DT crap.
> 
> I don't know who was right, but the fact is they won't be inclined to
> take such an approach unless the virtual demuxer is not exposed in the
> DT, which is almost impossible since irq users are identifying their
> irq lines with a phandle to the interrupt controller and an interrupt
> id (usually extracted from the datasheet).

I really have no idea why DT folks think that virtual devices are not
suitable for DT entries. Marks working assumption from the old thread:

 > This sounds like a DT-workaround for a Linux implementation problem,
 > and I don't think this the right way to solve your problem.

is simply wrong. This has nothing to do with a Linux implementation
problem. It's a sensible workaround for braindamaged hardware at the
proper abstraction level.

> Anyway, below is a solution providing a way to disable specific
> handlers without reworking the way we are modeling shared interrupts.
> Thomas, I know you were not in favor of the proposed approach, but,
> AFAICT, it does not add any conditional path to the interrupt handling
> path (which, IIRC, was one of your requirements), and is simple enough
> to be used by people really needing it.
> 
> There's probably other drawback I haven't noticed, so please don't
> hesitate to share your thoughts.

Yes, aside of the bloat, it needs special handling in free_irq() as
well.

Thanks,

	tglx


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