linux-kernel - Re: [PATCH] drm: ignore disconnected <-> unknown status changes

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Date:	Sun, 5 Aug 2012 23:06:11 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Alex Deucher <alexdeucher@...il.com>
Cc:	Knut Petersen <Knut_Petersen@...nline.de>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm: ignore disconnected <-> unknown status changes

On Fri, Aug 03, 2012 at 09:32:44AM -0400, Alex Deucher wrote:
> On Thu, Aug 2, 2012 at 3:21 AM, Knut Petersen <Knut_Petersen@...nline.de> wrote:
> > On an AOpen i915GMm-hfs the hotplug events generated
> > by transitions between connector_status_unknown and
> > connector_status_disconnected cause screen distortions.
> >
> > The attached patch cures the problem by disabling the
> > generation of hotplug events in those cases. That should
> > be safe for everybody as the only relevant changes are
> > those from / to connector_status_connected.
> 
> Seems reasonable to me.  We should just drop unknown.

We (ab)use that in i915 to avoid some (more costly) load-detection tricks
in the hotplug code (but only on rather ancient hw), instead returning
unknown. When userspace then inquires the connector status, we flip-flop
back to connected. The issue is that we need to avoid these, for the
current kms locking would stall the cursor for a while, which is not
acceptable to do every 10s. Until the kms locking is fixed, we hence can't
drop the unknown state.

> Reviewed-by: Alex Deucher <alexander.deucher@....com>
Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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