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

From: Chris Wilson
Date: Mon Jan 24 2011 - 14:13:33 EST

On Mon, 24 Jan 2011 19:48:55 +0100, Knut Petersen <Knut_Petersen@xxxxxxxxxxx> wrote:
> 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).

DVI detection is essentially retrieving the EDID by bitbanging on the DDC.
This is timing sensitive and I suspect that is being interrupted by the
system activity causing the EDID data to be returned corrupted. Is that
supported by any warnings in dmesg? Does increasing the drm.debug level to
0x6 reveal any more significant information?

Not sure how using the unaccelerated fbcon ties in just yet. It's an extra
source of latency vs X, but I would expect to impact upon DVI detection.

You can simply disable the polling with
'echo n > /sys/module/drm_kms_helper/parameter/poll'

Chris Wilson, Intel Open Source Technology Centre
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at