linux-kernel - Re: [PATCH 0/5] ACPI probing infrastructure

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Date:	Wed, 09 Sep 2015 00:26:03 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Len Brown <lenb@...nel.org>, Hanjun Guo <hanjun.guo@...aro.org>,
	Tomasz Nowicki <tn@...ihalf.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	linaro-acpi@...ts.linaro.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/5] ACPI probing infrastructure

On Tuesday, September 08, 2015 10:45:58 AM Marc Zyngier wrote:
> On 07/09/15 22:26, Rafael J. Wysocki wrote:
> > On Friday, September 04, 2015 06:06:47 PM Marc Zyngier wrote:
> >> IRQ controllers and timers are the two types of device the kernel
> >> requires before being able to use the device driver model.
> >>
> >> ACPI so far lacks a proper probing infrastructure similar to the one
> >> we have with DT, where we're able to declare IRQ chips and
> >> clocksources inside the driver code, and let the core code pick it up
> >> and call us back on a match. This leads to all kind of really ugly
> >> hacks all over the arm64 code and even in the ACPI layer.
> >>
> >> It turns out that providing such a probing infrastructure is rather
> >> easy, and provides a much deserved cleanup in both the arch code, the
> >> GIC driver, and the architected timer driver.
> > 
> > Since I'm not familiar with the DT probing infrastructure mentioned above,
> > can you please explain to me (possibly at a high level), how it is supposed
> > to work in the ACPI case?
> 
> So let's start with DT. Each interrupt controller driver has at least
> one entry like this:
> 
> IRQCHIP_DECLARE(gic_400, "arm,gic-400", gic_of_init);
> 
> which says: if you find a node having "arm,gic-400" as a compatible
> string in the device tree, then call gic_of_init with this node as a
> parameter. The probing itself is done by the OF layer when the
> architecture code calls of_irq_init() (usually via irqchip_init).
> 
> This has a number of benefits:
> 
> - The irqchip code is self-contained. No architecture specific entry
> point, no exposed symbols. Just a standard interface.
> 
> - The low-level architecture code doesn't have to know about which
> interrupt controller is present. It just calls into the firmware
> interface (of_irq_init) which is going to sort things out.
> 
> Similar infrastructure is provided for the timers/clock sources. Note
> that this is not a replacement for the device model, but acts as a
> probing infrastructure for things that are required too early for the
> device infrastructure to be available.
> 
> What I'm aiming for is to introduce the same level of abstraction for
> ACPI, or at least for the few bits that are required before a full blown
> ACPI/device model can be used. For this, I introduce something  vaguely
> similar:
> 
> IRQCHIP_ACPI_DECLARE(gic_v2, ACPI_MADT_TYPE_GENERIC_DISTRIBUTOR,
> 		     gic_validate_dist, ACPI_MADT_GIC_VERSION_V2,
> 		     gic_v2_acpi_init);
> 
> which says: if you find a ACPI_MADT_TYPE_GENERIC_DISTRIBUTOR entry in
> MADT (implied by the macro), and that entry is of type
> ACPI_MADT_GIC_VERSION_V2 (as checked by gic_validate_dist), then call
> gic_v2_acpi_init with the entry as a parameter. A bit more convoluted,
> but still without any special entry point.
> 
> The various interrupt controller drivers can then implement the above,
> and the arch code can use a firmware-specific call to get the probing
> done, still being oblivious of what interrupt controller is being used.
> It also makes the adaptation of a DT driver to ACPI easier.
> 
> Does this help?

Yes it does, thanks!

Rafael

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