linux-kernel - Re: [PATCH v2 1/5] irqchip: add dumb demultiplexer implementation

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Date:	Tue, 20 Jan 2015 14:08:53 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Rob Herring <robherring2@...il.com>
cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] irqchip: add dumb demultiplexer implementation

On Thu, 15 Jan 2015, Rob Herring wrote:
> On Thu, Jan 15, 2015 at 3:11 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > On Wed, 14 Jan 2015, Rob Herring wrote:
>
> > We do not change shared interrupts in any way. We provide an
> > alternative mechanism for braindead hardware. And if the at91 folks
> > are fine with the DT change, then it's their decision. Nothing forces
> > this on everyone.
> 
> We are changing how shared interrupts are described in DT. We don't
> need 2 ways to describe them. We could say this is only for AT91 and
> continue to describe shared interrupts as has been done forever. Then
> the next platform that hits this problem will have to go thru the same
> ABI breakage. Or we change DT practices to describe all shared
> interrupts with a demux node. Given the way DTs are incrementally
> created, it is not something we can check with review or tools, so we
> will still have the same ABI breakage problem.

This is not describing the proper shared interrupts. This is a special
case for a special case of braindamaged hardware. Whats wrong with
doing that? We dont have to change that for all shared interrupts
because 99% of them have a proper hardware implementation and are not
affected by this.

What's wrong with serving the AT91 with a proper solution, which does
NOT inflict horrible hacks into the core code and does NOT weaken
sanity checks and does NOT require irq chip specific knowledge in
device drivers?

> >> There are probably ways to do this demux irqchip without a DT change.

So far you have not provided any useful hint how to do so.

> > What's the problem with a DT change for a single platform, if the
> > maintainers are willing to take it and deal with the fallout?
> 
> What's the solution for a platform that an ABI break is not okay and
> can't deal with the fallout?

There is no other platform affected. This is a break for a specific
set of devices and the 'fallout' is confined, well known and accepted.

So what's your problem, really?

Thanks,

	tglx
 
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