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

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Message-ID: <53C296C2.30304@metafoo.de>
Date:	Sun, 13 Jul 2014 16:25:06 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Richard Weinberger <richard@....at>
CC:	Lennox Wu <lennox.wu@...il.com>, Marek Vasut <marex@...x.de>,
	Chen Gang <gang.chen.5i5j@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dmitry.torokhov@...il.com, thierry.reding@...il.com,
	jic23@...nel.org, wim@...ana.be,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	kys@...rosoft.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
	teg@...m.no, Mischa.Jonker@...opsys.com, msalter@...hat.com,
	knaack.h@....de, rdunlap@...radead.org,
	linux-input@...r.kernel.org, linux-pwm@...r.kernel.org,
	linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
	linux-watchdog@...r.kernel.org, Liqin Chen <liqin.linux@...il.com>
Subject: Re: [PATCH] drivers: Let several drivers depends on HAS_IOMEM for
 'devm_ioremap_resource'

On 07/13/2014 04:03 PM, Richard Weinberger wrote:
> Am 13.07.2014 15:56, schrieb Lars-Peter Clausen:
>> On 07/13/2014 03:40 PM, Richard Weinberger wrote:
>>> Am 13.07.2014 15:26, schrieb Lars-Peter Clausen:
>>>> On 07/13/2014 11:45 AM, Richard Weinberger wrote:
>>>>> Am 13.07.2014 11:27, schrieb Lennox Wu:
>>>>>> As I said before, some configurations don't make sense.
>>>>>
>>>>> If such a configuration can be achieved using allmod/yesconfig it has to be fixed.
>>>>> Chen's fixes seem reasonable as not all architectures support iomem.
>>>>
>>>> Maybe we should stub out ioremap() and friends when COMPILE_TEST is enabled to avoid these linker errors. That's in my opinion better than turning most of the 'depends on
>>>> COMPILE_TEST' into 'depends on COMPILE_TEST && HAS_IOMEM'. The issue comes up quite a lot and it is often overlooked when adding a driver that can be build when COMPILE_TEST is
>>>> enabled.
>>>
>>> And what should this stub do?
>>> Except calling BUG()...
>>
>> return NULL;
>>
>> It's for compile testing, it's not meant to work at runtime.
>
> Hm, I really don't like the idea of having a non-working kernel.
> IMHO either it should build _and_ run and nothing else.
> Greg, what do you think?

The kernel will still be working fine and you can run it on a system. The 
drivers which use ioremap() or similar are probably not instantiated on a 
system that does not provide HAS_IOMEM. But even if it was the driver should 
handle ioremap() returning NULL gracefully and abort the driver probe. That 
said you'll probably not run a kernel that was built with COMPILE_TEST on your 
real hardware since it contains so many drivers that are completely useless on 
your hardware. The idea of COMPILE_TEST is to have as much compile test 
exposure as possible to the code that is enabled by COMPILE_TEST. Stubbing out 
ioremap() and friends when HAS_IOMEM is not set and COMPILE_TEST is set makes 
it easier to get there.

- Lars

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