linux-kernel - Re: [PATCH] drivers: Let several drivers depends on HAS_IOMEM for 'devm_ioremap

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Message-ID: <53C869D3.6030908@gmail.com>
Date:	Fri, 18 Jul 2014 08:26:59 +0800
From:	Chen Gang <gang.chen.5i5j@...il.com>
To:	Arnd Bergmann <arnd@...db.de>, Chris Metcalf <cmetcalf@...era.com>
CC:	Lars-Peter Clausen <lars@...afoo.de>,
	Guenter Roeck <linux@...ck-us.net>,
	Richard Weinberger <richard@....at>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	dmitry.torokhov@...il.com, linux-iio@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>, teg@...m.no,
	Thierry Reding <thierry.reding@...il.com>,
	Lennox Wu <lennox.wu@...il.com>, Marek Vasut <marex@...x.de>,
	Liqin Chen <liqin.linux@...il.com>, msalter@...hat.com,
	linux-pwm@...r.kernel.org, devel@...verdev.osuosl.org,
	linux-watchdog@...r.kernel.org, linux-input@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	knaack.h@....de, Martin Schwidefsky <schwidefsky@...ibm.com>,
	Mischa.Jonker@...opsys.com, jic23@...nel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH] drivers: Let several drivers depends on HAS_IOMEM for
 'devm_ioremap_resource'

On 07/18/2014 05:05 AM, Arnd Bergmann wrote:
> On Thursday 17 July 2014 16:41:14 Chris Metcalf wrote:
>> On 7/17/2014 7:28 AM, Chen Gang wrote:
>>> On 07/17/2014 06:48 PM, Arnd Bergmann wrote:
>>>> AFAICT, NO_IOMEM only has a real purpose on UML these days. Could we take
>>>> a shortcut here and make COMPILE_TEST depend on !UML? Getting random stuff
>>>> to build on UML seems pointless to me and we special-case it in a number of
>>>> places already.
>>>>
>>> According to current source code, tile still has chance to choose
>>> NO_IOMEM, for me, welcome the tile's maintainer's ideas or suggestions.
>>
>> I'm not really sure.  It's true that on tile, if you don't enable PCI
>> support there's no other I/O memory (or I/O port) space you can use.
>> We pretty much always enable PCI support in our kernel, though.  I'm
>> kind of surprised that other architectures don't also have the model
>> that IOMEM requires PCI, but perhaps most architectures just don't
>> encode that in the Kconfig file?
> 
> Only s390 as far as I know. Most architectures have integrated
> peripherals that use MMIO without PCI.
> 
>> My observation is just that if I remove the "NO_IOMEM if !PCI" from
>> arch/tile/Kconfig, my build fails with ioremap() undefined.  No doubt I
>> could work around that, but my assumption was that NO_IOMEM was exactly the
>> right thing to express the fact that without PCI there is no I/O memory 
> 
> Your assumption is correct.
> 
> For tile by itself it would certainly be best to leave this
> dependency, it makes no sense to enable IOMEM without PCI.
> 
> That doesn't solve the problem of COMPILE_TEST enabling drivers
> that require IOMEM though. An easy hack for that would be to
> make COMPILE_TEST depend on HAS_IOMEM, but it gets into hacky territory
> there, and it's not clear if this is any better than the original patch
> to provide fallbacks for ioremap and friends. Definitely simpler
> though.
> 

OK, thank all of you, tile just likes most of architectures to support
IOMEM, and at present, we can focus score and uml only.

Thanks.
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed
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