linux-kernel - Re: 2.6.29-rc3-git6: Reported regressions from 2.6.28

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Date:	Thu, 5 Feb 2009 20:12:34 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Eric Anholt <eric@...olt.net>,
	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


* Randy Dunlap <randy.dunlap@...cle.com> wrote:

> 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.

Check the patch i posted in this thread earlier today, it solves this 
problem.

	Ingo
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