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

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Message-ID: <53C2DF12.6040507@nod.at>
Date:	Sun, 13 Jul 2014 21:33:38 +0200
From:	Richard Weinberger <richard@....at>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lars-Peter Clausen <lars@...afoo.de>
CC:	dmitry.torokhov@...il.com, linux-iio@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>, teg@...m.no,
	thierry.reding@...il.com, Lennox Wu <lennox.wu@...il.com>,
	Chen Gang <gang.chen.5i5j@...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
Subject: Re: [PATCH] drivers: Let several drivers depends on HAS_IOMEM for
 'devm_ioremap_resource'

Am 13.07.2014 21:22, schrieb Greg Kroah-Hartman:
> On Sun, Jul 13, 2014 at 04:25:06PM +0200, Lars-Peter Clausen wrote:
>> 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.
> 
> I run my kernels with COMPILE_TEST enabled as I need to build test
> things that I don't happen to use.
> 
> I like the 'return NULL' option for this, it hits us all the time, might
> as well fix it properly like this so that we don't have to deal with
> Kconfig changes everywhere.
> 
> Also put a big "This platform does not support IOMEM" error printk in
> there, so that people have a chance to figure out what is going on if
> they happen to run such a driver on a platform that can't support it.

Maybe we could add COMPILE_TEST to the version string too?
Just to detect such kernels fast in user bug reports...

Thanks,
//richard
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