linux-kernel - Re: [PATCH v2 0/5] ACPI probing infrastructure

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Date:	Sat, 26 Sep 2015 01:45:42 +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 v2 0/5] ACPI probing infrastructure

On Sunday, September 13, 2015 03:02:18 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.
> 
> The Device Tree infrastructure makes it very easy to make these
> discoverable by the rest of the kernel. For example, 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 oblivious to what interrupt controller is being used. It
> also makes the adaptation of a DT driver to ACPI easier.
> 
> 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.
> 
> I'm sure there is some more code to be deleted, and one can only
> wonder why this wasn't done before the arm64 code was initially merged
> (the diffstat says it all...).
> 
> Patches are against v4.3-rc1, and a branch is available at
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git acpi/device-probing-v2
> 
> * From the initial version:
>   - Make the infrastructure more DT like by providing an
>     acpi_probe_entry array per "device type" (one for irqchips, one
>     for clocksources). This means that entries can depend on any ACPI
>     static table.
>   - Use some cpp magic to reduce the amount of code added to an
>     absolute minimum.
>   - Rebased on v4.3-rc1
> 
> Marc Zyngier (5):
>   acpi: Add basic device probing infrastructure
>   irqchip/acpi: Add probing infrastructure for ACPI-based irqchips
>   irqchip/gic: Convert the GIC driver to ACPI probing
>   clocksource/acpi: Add probing infrastructure for ACPI-based
>     clocksources
>   clocksource/arm_arch_timer: Convert to ACPI probing

I'm generally fine with this (modulo a couple of super-minor nits in the
first patch), but it needs ACKs from Thomas for the irqchip-related and
clocksource-related patches.

Plus [3/5] needs to be rebased on top of the Al's patches removing BAD_MADT_ENTRY
(currently in my bleeding-edge branch).

Thanks,
Rafael

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