Message-ID: <498B1F2A.70209@oracle.com>
Date:	Thu, 05 Feb 2009 09:17:30 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Eric Anholt <eric@...olt.net>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Norbert Preining <preining@...ic.at>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>,
	samr <sam@...nborg.org>
Subject: Re: 2.6.29-rc3-git6: Reported regressions from 2.6.28

Eric Anholt wrote:
> On Wed, 2009-02-04 at 19:56 +0100, Ingo Molnar wrote:
>> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>>
>>> On Wed, 4 Feb 2009, Norbert Preining wrote:
>>>> The problem is that if you have a configuration under 2.6.28 without 
>>>> CONFIG_FB and just call make oldconfig, or even make config and don't 
>>>> know that you loose the DRM. And I was using make oldconfig (there is a 
>>>> graphical config?? ;-))
>>> Sure. It's inconvenient, no question about that. I asked the i915 people 
>>> to look into not requiring CONFIG_FB, and I hope they will, but my point 
>>> is that I don't think we can consider "small one-time inconvenience" to be 
>>> a "regression".
>> if you mean that as a general principle, there's four very real downsides in 
>> my opinion.
>>
>> Firstly, we could have done better (and still can do better), via various 
>> easy and non-intrusive measures:
>>
>>    - We could add a runtime warning:
>>
>>       for example a WARN_ONCE("please enable CONFIG_DRM_I915 and CONFIG_FB") 
>>       that there's no DRM because CONFIG_FB is not selected and oldconfig 
>>       loses the I915 setting silently - placed in a key DRM ioctl, would 
>>       have gone a long way addressing the issue. Testers do notice kernel 
>>       warnings that pop up when their X gets slow. (This approach might also 
>>       have the added bonus of warning folks who enable the wrong driver for 
>>       the hardware.)
>>
>>    - Or we could add a more thoughtful Kconfig migration:
>>
>>       Rename DRM_I915 to DRM_I915_FB [which it really is now], and keep
>>       DRM_I915 as a non-interactive migration helper: if set, it 
>>       auto-selects both FB and DRM_I915_FB.
>>
>>       While CONFIG_FB is an interactive Kconfig option so a select can be 
>>       dangerous to a correct dependency tree, it seems safe to do in this 
>>       specific case because it seems to be a rather leaf entry with no 
>>       dependencies.
> 
> I tried select FB.  It's the right thing to do.  It doesn't work.  I
> posted to the mailing list two weeks ago about the insane dependency
> chain that kbuild comes up with and fails on when we do this, and got
> silence.

I tried what you had described in that email (from 2 weeks ago), got the
same results that you did, but kbuild does seem very confused (to me).

reference email from 2+ weeks ago:
  http://marc.info/?l=linux-kernel&m=123197341316461&w=2

Adding Sam to cc.

> Believe me, I hate this inconvenience to users even more than each of
> you do, because I get to deal with the reports.  But I haven't had the
> time to sit down and figure out what drugs kbuild is on, or even how to
> work around it (despite IRC help from a few other kernel guys).
> 
> The alternative I can see is to ifdef the code for something that will
> be on by default and which stable userland will require in 6 months.
> That seems wrong.
> 


-- 
~Randy
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