linux-kernel - Re: [Linaro-acpi] [RFC part1 PATCH 1/7] ACPI: Make ACPI core running without PCI on ARM64

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Date:	Mon, 09 Dec 2013 12:12:24 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>
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>,
	patches@...aro.org, Olof Johansson <olof@...om.net>,
	Catalin Marinas <catalin.marinas@....com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, Will Deacon <will.deacon@....com>,
	linaro-acpi@...ts.linaro.org, linux-acpi@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [Linaro-acpi] [RFC part1 PATCH 1/7] ACPI: Make ACPI core running
 without PCI on ARM64

On 2013-12-7 1:23, Arnd Bergmann wrote:
> On Friday 06 December 2013, Tomasz Nowicki wrote:
>> On 05.12.2013 23:04, Arnd Bergmann wrote:
>>> On Wednesday 04 December 2013, Hanjun Guo wrote:
>>>> On 2013年12月04日 00:41, Matthew Garrett wrote:
>>>>> Given the number of #ifdefs you're adding, wouldn't it make more sense
>>>>> to just add stub functions to include/linux/pci.h?
>>>>
>>>> Thanks for the suggestion :)
>>>>
>>>> I can add stub functions in include/linux/pci.h for raw_pci_read()/
>>>> raw_pci_write(), then can remove #ifdefs for acpi_os_read/write_pci_configuration().
>>>
>>> Actually I wonder about the usefulness of this patch in either form: Since ACPI
>>> on ARM64 is only for servers, I would very much expect them to always come with
>>> PCI, either physical host bridges with attached devices, or logical PCI functions
>>> used to describe the on-SoC I/O devices. Even in case of virtual machines, you'd
>>> normally use PCI as the method to communicate data about the virtio channels.
>>>
>>> Can you name a realistic use-case where you'd want ACPI but not PCI?
>>
>> Yes you can describe SoC I/O devices using logical PCI functions only if 
>> they are on PCI, correct me if I am wrong. Also, devices can be placed 
>> only on IOMEM (like for ARM SoC) and it is hard to predict which way 
>> vendors chose. So way don't let it be configurable? ACPI spec says 
>> nothing like PCI is needed for ACPI, AFAIK.
> 
> You are right that today's ARM SoCs basically never use PCI to describe
> internal devices (IIRC VIA VT8500 is an exception, but their PCI was
> just a software fabrication).
> 
> However, when we're talking about ACPI on ARM64, that is nothing like classic
> ARM SoCs: As Jon Masters mentioned, this is about new server hardware following
> a (still secret, but hopefully not much longer) hardware specification that is
> explicitly designed to allow interoperability between vendors, so they
> must have put some thought into how to make the hardware discoverable. It
> seems that they are modeling things after how it's done on x86, and the
> only sensible way to have discoverable hardware there is PCI. This is
> also what all x86 SoCs do.

I think the concern here is that ACPI is only for server platform or not.

Since ACPI has lots of content related to power management, I think ACPI
can be used for mobile devices and other platform too, not only for ARM
servers, and with this patch, we can support both requirement.

Thanks
Hanjun
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