linux-kernel - Re: [RFC PATCH] media: consolidation of -I flags

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Date:	Tue, 5 Oct 2010 16:29:06 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	matt mooney <mfm@...eddisk.com>
Cc:	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Michal Marek <mmarek@...e.cz>, linux-media@...r.kernel.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [RFC PATCH] media: consolidation of -I flags

On Sun, Sep 26, 2010 at 02:00:47PM -0700, matt mooney wrote:
> I have been doing cleanup of makefiles, namely replacing the older style
> compilation flag variables with the newer style. While doing this, I
> noticed that the majority of drivers in the media subsystem seem to rely
> on a few core header files:
> 
> 	-Idrivers/media/video
> 	-Idrivers/media/common/tuners
> 	-Idrivers/media/dvb/dvb-core
> 	-Idrivers/media/dvb/frontends
> 
> This patch removes them from the individual makefiles and puts them in
> the main makefile under media.
Using subdir-ccflags-y has one drawback you need to be aware of.
The variable is _not_ picked up if you build individual drivers like
this:

     make drivers/media/dvb/b2c2/

So with this patch applied it is no longer possible to do so.
It is better to accept the duplication rather than breaking
the build of individual drivers.

> 
> If neither idea is considered beneficial, I will go ahead and replace
> the older variables with the newer ones as is.

This is the right approach.

You could consider to do a more general cleanup:
1) replace EXTRA_CFLAGS with ccflags-y (the one you suggest)
2) replace use of <module>-objs with <module>-y
3) break continued lines into several assignments
   People very often uses '\' to break long lines, where a
   simple += would be much more readable.
   But this topic may be personal - I never uses "\" in my .c code unless in macros,
   and I have applied the same rule for Makefiles.
   An ugly example is drivers/media/Makefile
4) In general use ":=" instead of "=".
   Add using "+=" as first assignment is OK - but it just looks plain wrong
5) some files has a mixture of spaces/tabs (are red in my vim)
   dvb-core/Makefile is one such example
6) remove useless stuff
   siano/Makefile has some strange assignments to EXTRA_CFLAGS
7) Likely a few more items to look after...

This is more work - but then you finish a Makefile rather than doing a simple
conversion.

	Sam
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