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Date:	Thu, 03 Jan 2013 22:45:36 +0000
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexey Zaytsev <alexey.zaytsev@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Rodrigo Vivi <rodrigo.vivi@...il.com>,
	Peter Ujfalusi <peter.ujfalusi@...il.com>,
	stable <stable@...r.kernel.org>
Subject: Re: Linux 3.8-rc2

On Thu, 3 Jan 2013 13:32:04 -0800, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Thu, Jan 3, 2013 at 1:09 PM, Alexey Zaytsev <alexey.zaytsev@...il.com> wrote:
> >
> > i915 got broken on my machine (Lenovo ThinkPad SL500) by this -rc. The screen
> > goes blank after loading the module. I've bisected the problem to
> > b0a2658acb5bf9ca86b4aab011b7106de3af0add "drm/i915: don't disable
> > disconnected outputs".
> 
> Hmm. Daniel - should I just revert it, or do you have a patch to
> possibly fix the divide-by-zero error in g4x_compute_wm0() (which may
> involve not getting that deep in the call chain to begin with or
> whatever)? Maybe that fixes the blank screen too without a revert..

The issue appears to be a disagreement between intel_crtc->active, an
attached framebuffer and there not being a valid mode set on the crtc.

It looks like we end up in that situation with further confusion over
intel_crtc->base.enabled vs intel_crtc->active. I suspect the answer is
something like:

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index a9fb046..5e4b818 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -7940,10 +7940,8 @@ bool intel_set_mode(struct drm_crtc *crtc,
 		}
 	}
 
-	for_each_intel_crtc_masked(dev, prepare_pipes, intel_crtc) {
-		if (intel_crtc->base.enabled)
-			dev_priv->display.crtc_disable(&intel_crtc->base);
-	}
+	for_each_intel_crtc_masked(dev, prepare_pipes, intel_crtc)
+		dev_priv->display.crtc_disable(&intel_crtc->base);
 
 	/* crtc->mode is already used by the ->mode_set callbacks, hence we need
 	 * to set it here already despite that we pass it down the callchain.

However, until that confusion is unravelled, reverting b0a2658ac, seems
the most sensible approach.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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