Date:	Tue, 18 Jun 2013 06:51:32 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Jeff Mahoney <jeffm@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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>, tomi.valkeinen@...com
Subject: Re: [PATCH] build some drivers only when compile-testing

Dne 17.6.2013 22:05, Jiri Slaby napsal(a):
> 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 ;).

I agree with Sam. 'depends on XY || COMPILE_TEST' is quite
self-explanatory. And even if it's not, you can look up the help text
for COMPILE_TEST. With "archdepends on" or "available on", you need to
know what to look for to override the dependency.

Michal
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