linux-kernel - Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip

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Message-ID: <20150211133859.GC3971@piout.net>
Date:	Wed, 11 Feb 2015 14:38:59 +0100
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"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>
Subject: Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq
 demuxer chip

On 11/02/2015 at 12:36:56 +0000, Mark Rutland wrote :
> > Actually, that was one of the requirements expressed by Thomas (Thomas,
> > correct me if I'm wrong).
> > The point was to force shared irq users to explicitly specify that they
> > are mixing !IRQF_NO_SUSPEND and IRQF_NO_SUSPEND because they have no
> > other choice.
> > 
> > With your patch, there's no way to inform users that they are
> > erroneously setting the IRQF_NO_SUSPEND flag on one of their shared
> > interrupt.
> 
> Sure, but even with the demux that's still the case (because it pretends
> that this mismatch is a HW property rather than a property of the set of
> drivers sharing the interrupt).
> 
> Whether there's a demux node in the DTB is entirely separate from
> whether the drivers can actually handle the situation.
> 
> So if we need a warning in the presence of mismatch and action masking,
> we need the exact same warning with the demux.
> 

Actually, we only care about removing the warning. It is effectively the
HW that forces us to do so. So we would be completely happy with a new
flag to silence the warning as we know what we are doing (I think that
has already been suggested).

> The presence of a demux implies the DTB author believes they have solved
> the problem with the demux, not necessarily that they have considered
> the situation and updated drivers appropriately. Relying on the demux to
> imply that everything is fine only gives us the illusion that everything
> is fine.
> 

Whatever the solution, it could be used as a workaround the warning as
this is exactly what we need for our platform.


-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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