Date:	Mon, 17 Jun 2013 22:05:19 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Jeff Mahoney <jeffm@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	jirislaby@...il.com, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-usb@...r.kernel.org,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	linux-geode@...ts.infradead.org, linux-fbdev@...r.kernel.org,
	Richard Cochran <richardcochran@...il.com>,
	netdev@...r.kernel.org, Ben Hutchings <ben@...adent.org.uk>,
	"Keller, Jacob E" <jacob.e.keller@...el.com>,
	Michal Marek <mmarek@...e.cz>, tomi.valkeinen@...com
Subject: Re: [PATCH] build some drivers only when compile-testing

On 05/23/2013 05:09 AM, Jeff Mahoney wrote:
> On 5/22/13 10:23 PM, Greg Kroah-Hartman wrote:
>> On Wed, May 22, 2013 at 11:18:46AM +0200, Jiri Slaby wrote:
>>> Some drivers can be built on more platforms than they run on. This
>>> causes users and distributors packaging burden when they have to
>>> manually deselect some drivers from their allmodconfigs. Or sometimes
>>> it is even impossible to disable the drivers without patching the
>>> kernel.
>>>
>>> Introduce a new config option COMPILE_TEST and make all those drivers
>>> to depend on the platform they run on, or on the COMPILE_TEST option.
>>> Now, when users/distributors choose COMPILE_TEST=n they will not have
>>> the drivers in their allmodconfig setups, but developers still can
>>> compile-test them with COMPILE_TEST=y.
>>
>> I understand the urge, and it's getting hard for distros to handle these
>> drivers that just don't work on other architectures, but it's really
>> valuable to ensure that they build properly, for those of us that don't
>> have many/any cross compilers set up.

But this is exactly what COMPILE_TEST will give us when set to "y", or
am I missing something?

>>> Now the drivers where we use this new option:
>>> * PTP_1588_CLOCK_PCH: The PCH EG20T is only compatible with Intel Atom
>>>   processors so it should depend on x86.
>>> * FB_GEODE: Geode is 32-bit only so only enable it for X86_32.
>>> * USB_CHIPIDEA_IMX: The OF_DEVICE dependency will be met on powerpc
>>>   systems -- which do not actually support the hardware via that
>>>   method.
>>
>> This seems ripe to start to get really messy, really quickly.  Shouldn't
>> "default configs" handle if this "should" be enabled for a platform or
>> not, and let the rest of us just build them with no problems?
> 
> If every time a new Kconfig option is added, corresponding default
> config updates come with it, sure. I just don't see that happening,
> especially when it can be done much more clearly in the Kconfig while
> the developer is writing the driver.
> 
>> What problems is this causing you?  Are you running out of space in
>> kernel packages with drivers that will never be actually used?
> 
> Wasted build resources. Wasted disk space on /every/ system the kernel
> package is installed on. We're all trying to pare down the kernel
> packages to eliminate wasted space and doing it manually means a bunch
> of research, sometimes with incorrect assumptions about the results,
> needs to be done by someone not usually associated with that code. That
> research gets repeated by people maintaining kernel packages for pretty
> much every distro.

I second all the above.

>>> +config COMPILE_TEST
>>> +	bool "Compile also drivers which will not load" if EXPERT
>>
>> EXPERT is getting to be the "let's hide it here" option, isn't it...
>>
>> I don't know, if no one else strongly objects, I can be convinced that
>> this is needed, but so far, I don't see why it really is, or what this
>> is going to help with.
> 
> I'm not convinced adding a || COMPILE_TEST option to every driver that
> may be arch specific is the best way to go either. Perhaps adding a new
> Kconfig verb called "archdepends on" or something that will evaluate as
> true if COMPILE_TEST is enabled but will evaluate the conditional if
> not. *waves hands*

Sam Ravnborg (the kconfig ex-maintainer) once wrote that he doesn't want
to extend the kconfig language for this purpose (which I support). That
a config option is fine and sufficient in this case [1]. Except he
called the config option "SHOW_ALL_DRIVERS". Adding the current
maintainer to CCs ;).

[1] http://comments.gmane.org/gmane.linux.kbuild.devel/9829

The last point I inclined to the Greg's argument to remove the EXPERT
dependency.

So currently I have what is attached... Comments?

thanks,
-- 
js
suse labs

View attachment "0001-build-some-drivers-only-when-compile-testing.patch" of type "text/x-patch" (5334 bytes)

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