linux-kernel - Re: Linux 2.6.26-rc1

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Date:	Tue, 6 May 2008 19:39:28 -0300
From:	Mauro Carvalho Chehab <mchehab@...radead.org>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	Alistair John Strachan <alistair@...zero.co.uk>,
	Robin Holt <holt@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.26-rc1

On Tue, 06 May 2008 22:47:20 +0200
Stefan Richter <stefanr@...6.in-berlin.de> wrote:

> Mauro Carvalho Chehab wrote:
> > For example, if you have a em28xx device with msp3400 and tvp5150 and another
> > em28xx device with saa7113.
> > 
> > If you remove the select's for MSP3400, TVP5150 and SAA7113, at, em28xx, the
> > module will compile without problems.
> > 
> > The only issue is that you won't be able to see any images (due to the lack of
> > tvp5150 or saa7113 analog TV demoduler) or listen to the audio, if the device
> > needs msp3400 to decode audio.
> [...]
> > It is much better for the user to just select EM28XX and let the Kconfig do the
> > hard work of selecting what low-level driver applies for em28xx-based devices.
> > 
> > This causes lots of select, being very hard to maintain. The better would be to
> > have a select-like clause that could check the dependencies automatically.
> > 
> > Another alternative would be some sort of script (checkpatch.pl?) that would
> > check if all selected dependencies are ok.
> 
> Ah, now I understand.  You use "select" to enable options which aren't 
> actually a build requirement for the selecting option.

Yes. That's why there are so many selects. Just a few of them are really to
select "real" build requirements.

> Another workaround for this UI limitation:
> 
> config VIDEO_EM28XX
> 	tristate "Empia EM2800/2820/2840 USB video capture support"
> 	depends on WHATEVER_BUILD_REQUIREMENT_IS_LEFT
> 	select MAYBE_ANOTHER_BUILD_REQUIREMENT
> 	help
> 	  ...
> 
> comment "Empia EM28xx devices may require Philips SAA7113/4/5 video 
> decoders"
> 	depends on VIDEO_EM28XX && VIDEO_SAA711X=n
> 
> comment "Empia EM28xx devices may require Texas Instruments TVP5150 
> video decoder"
> 	depends on VIDEO_EM28XX && VIDEO_TVP5150=n
> 
> Still awkward, but now you don't have to copy VIDEO_SAA711X's and 
> VIDEO_TVP5150's dependencies to VIDEO_EM28XX anymore.

This seems Interesting, but probably not very effective, since it would produce
a large amount of "warnings". However, we may use something like this:

comment "WARNING: Empia EM28xx devices require a video decoder"
 	depends on VIDEO_EM28XX && (VIDEO_TVP5150=n && VIDEO_SAA711X = n)

> 
> 
> Or another idea:
> 
> Copy _all_ dependencies of drivers which can be selected by "...if 
> VIDEO_HELPER_CHIPS_AUTO" to VIDEO_HELPER_CHIPS_AUTO.

I actually did this for tuners, on this changeset (still not at mainstream):
http://git.kernel.org/?p=linux/kernel/git/mchehab/v4l-dvb.git;a=commitdiff;h=d10b3c6817fb3fed8e6cd6d64d47c187a615c952

> 
> Of course all these issues go away as soon as somebody has implemented 
> "select" with recursive dependency check.

Yes.

Cheers,
Mauro
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