linux-kernel - Re: [PATCH v4 14/18] ARM64 / ACPI: Add GICv2 specific ACPI boot support

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Date:	Thu, 18 Sep 2014 04:25:29 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	"jcm@...hat.com" <jcm@...hat.com>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mark Rutland <Mark.Rutland@....com>,
	Olof Johansson <olof@...om.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Lv Zheng <lv.zheng@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Charles Garcia-Tobin" <Charles.Garcia-Tobin@....com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"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 14/18] ARM64 / ACPI: Add GICv2 specific ACPI boot support

On Wednesday 17 September 2014, Catalin Marinas wrote:
> > > I think it gets worse, this function is called from irqchip_init(). I
> > > would have been slightly happier if it was called from the arm64
> > > init_IRQ(). But putting an ARM specific GIC initialisation call in a
> > > generic irqchip_init() just looks weird. Can we do anything better here?
> > 
> > Yes this was discussed, please have a look at: 
> > https://lkml.org/lkml/2014/9/1/555
> > We had this in init_IRQ() in previous patch set, then we got feedback 
> > irqchip_init() is more appropriate. We can move it back to init_IRQ() 
> > and I am sold on this.
> 
> The irqchip_init() is indeed the place to call other interrupt
> controller initialisation functions but what I don't particularly like
> is calling the GIC one directly while the OF ones are checked against a
> match string. For GICv3 and later, do you plan to use the same
> acpi_gic_init() functions? Otherwise we could do something like
> ACPI_IRQCHIP_DECLARE() similar to the OF ones and a common function that
> probes whatever is built into the kernel.

I talked abouto this with Marc Z the other day, and I think it really
comes down to how we expect this to develop in the future:

If this is going to stay with the GICv2/v3/v4 line of interrupt controllers,
I see the ACPI_IRQCHIP_DECLARE() as total overdesign, since we wouldn't
ever need more than two entry points.

Doing ACPI_IRQCHIP_DECLARE() makes it possible to deal with other
incompatible irqchips as they come along, but also seems to invite
those.

Marc believes that it's inevitable that people will add lots of crazy
interrupt controllers to systems using ACPI and at that point I agree
it would be the right way to deal with it. However, I also think that
as long as people expect to be able to add lots of crazy interrupt
controller drivers, we are not ready to merge ACPI in the first place,
because it must first be clear to everybody that we are not going to
allow those nonstandard controller drivers to get merged.

	Arnd
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