linux-kernel - Re: [PATCH v3 0/7] Early ACPI probing infrastructure

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Date:	Tue, 29 Sep 2015 23:25:22 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	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>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	linaro-acpi@...ts.linaro.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 0/7] Early ACPI probing infrastructure

On 09/28/2015 10:49 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. An additional (and very
> much optional) patch renames files and symbols to make it obvious that
> the infrastructure is not just for DT anymore.
>
> 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 Rafael's bleeding-edge branch, and a branch is
> available at
>
> git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git acpi/device-probing-v3
>
> * From v2:
>    - Addressed Rafael's comments (title for patch #1, macro/field names)
>    - New config symbols for clocksources

I like this one most :)

>    - Additional and optional last patch to get rid of the apparent
>      dependency between the probing infrastructure and DT.
>
> * 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 (7):
>    acpi: Add early 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: Add new CLKSRC_{PROBE,ACPI} config symbols
>    clocksource/arm_arch_timer: Convert to ACPI probing
>    clocksource: cosmetic: Drop OF 'dependency' from symbols

Tested locally on QEMU (as I'm in home so no hardware is available) and
it boots as before with GICv2 and arch timer work ok (sure with ACPI),
for this patch set:

Tested-by: Hanjun Guo <hanjun.guo@...aro.org>

Thanks
Hanjun
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