linux-kernel - [BUG/REGRESSION] DRM / i915 / 2.6.37 and 2.6.38-rc*: DVI output gets disabled/reenabled under load

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Message-ID: <4D3DC997.5040605@t-online.de>
Date:	Mon, 24 Jan 2011 19:48:55 +0100
From:	Knut Petersen <Knut_Petersen@...nline.de>
To:	linux-kernel@...r.kernel.org
CC:	Chris Wilson <chris@...is-wilson.co.uk>, jesse.barnes@...el.com
Subject: [BUG/REGRESSION] DRM / i915 / 2.6.37 and 2.6.38-rc*: DVI output gets
 disabled/reenabled under load

On an AOpen i915GMm-HFS I see the following problem:
The LCD panel connected to DVI-1 gets disabled and then reenabled
under high system load (e.g. -j 15 kernel compile) if I am working on the
framebuffer console (no problems in X).

Kernels affected: 2.6.37, 2.6.38-rc1, 2.6.38-rc2
Kernel _not_ affected: 2.6.31.14, 2.6.36.3

Details: There is a DVI (DVI-1) connector and a VGA (VGA-1) connector
present.
The kernel also detects a connector VGA-2, but there is no hardware
connector for that.

I tried to bisect, but that did not provide a reasonable result because
of other problems
with the code.

Further inspection showed: The problem is related to the 10 second
connector rescan.

Idling at the prompt the status of VGA-2 is an almost stable
connector_status_unknown (3).
Under load that changes, the connector status is floating between
connector_status_unknown and connector_status_disconnected. During the
action
taken after a status changes DVI-1 temporarily gets disabled.

Disabling the connector rescan in the source code fixes the problem,
but obviously that is not the best possible fix ;-)

Knut
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