linux-kernel - Re: [PATCH v3 2/8] genirq: irqdomain: Remove irqdomain dependency on struct device

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Date:	Wed, 16 Sep 2015 11:00:26 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Marc Zyngier <marc.zyngier@....com>
cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Jason Cooper <jason@...edaemon.net>,
	linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Graeme Gregory <graeme@...a.org.uk>,
	Jake Oshins <jakeo@...rosoft.com>
Subject: Re: [PATCH v3 2/8] genirq: irqdomain: Remove irqdomain dependency
 on struct device_node

On Wed, 16 Sep 2015, Marc Zyngier wrote:
> On 16/09/15 02:53, Rafael J. Wysocki wrote:
> > I've just seen quite a few bugs where a pointer to something completely invalid
> > have been silently passed via (void *) which often results in very interesting
> > breakage (that is really hard to debug for that matter).
> 
> I actually tried to prototype this yesterday, and ended up in hell. The
> main issue is the point where the generic irqdomain code meets the DT
> subsystem (which is basically any interrupt controller, including those
> being ACPI driven). The domain_token to of_node path is dead easy, but
> you cannot do the reverse conversion, so this would have to spread
> around like a cancer. I gave up.
> 
> At this stage, I see two options: sticking with (void *) with the risk
> of breakage and subtle bugs which we all love to track down (not!), or
> do a major U-turn and make device_node a strict requirement for domain
> lookup.
> 
> After the above experiment, I now see some value in actually keeping
> device_node around, using it as the token, and allocating it when
> required (the typical case being those interrupt controllers that are
> both DT and ACPI). I'll play with it a bit more.

Right. We already have the fwnode_type in struct device_node, so we
can reuse it. If you care about the size of the struct, then you can
make some of the struct members conditional on CONFIG_OF.

Thanks,

	tglx

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