linux-kernel - Re: [PATCH 06/20] ARM64 / ACPI: Introduce some PCI functions when PCI is enabled

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Message-ID: <52DDEC3B.1000208@linaro.org>
Date:	Tue, 21 Jan 2014 11:40:43 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Mark Rutland <mark.rutland@....com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	linaro-kernel@...ts.linaro.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Rob Herring <robh@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	linaro-acpi@...ts.linaro.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	patches@...aro.org, Olof Johansson <olof@...om.net>,
	Charles.Garcia-Tobin@....com, Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	Grant Likely <grant.likely@...aro.org>
Subject: Re: [PATCH 06/20] ARM64 / ACPI: Introduce some PCI functions when
 PCI is enabled

On 2014-1-21 2:39, Arnd Bergmann wrote:
> On Monday 20 January 2014, Hanjun Guo wrote:
>>>> acpi_register_ioapic()/acpi_unregister_ioapic() will be used for IOAPIC
>>>> hotplug and GIC distributor is something like IOAPIC on x86, so I think
>>>> these two functions can be reserved for future use.
>>> But GIC is not hotplugged, is it? It still sounds x86 specific to me.
>>
>> Well, if we want to do physical CPU hotplug on ARM/ARM64 (maybe years 
>> later?),
>> then GIC add/remove is needed because we have to remove GIC
>> on the SoC too when we remove the physical CPU.
> 
> In general, I recommend not planning for the future in kernel code when you
> don't know what is going to happen. It's always easy enough to change
> things once you get there, as long as no stable ABI is involved.

Ok, I agree with you.

> 
> I just looked at the caller of these functions, and found a self-contained
> PCI driver in drivers/pci/ioapic.c, which uses two sepate PCI classes for
> ioapic and ioxapic. I think it's a safe assumption to say that even if we
> get ARM CPU+GIC hotplug, that would not use the same ioapic driver. This
> driver is currently marked X86-only, and that should probably stay this way,
> so you won't need the hooks.

Will find a suitable way to fix that in next version, thanks for you comments :)

Hanjun

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