[Intel-gfx] [PATCH 2/2] drm/crtc-helper: clamp unknown connector status in the poll work

[Chris Wilson]

On Thu, Jun 06, 2013 at 12:17:26AM +0200, Daniel Vetter wrote:
> On some chipset we try to avoid possibly invasive output detection
> methods (like load detect which can cause flickering elsewhere) in the
> output poll work. Drivers could hence return unknown when a previous
> full ->detect call returned a different state.
> 
> This change will generate a hotplug event, forcing userspace to do a
> full scan. This in turn updates the connector->status field so that we
> will _again_ get a state change when the hotplug work re-runs in 10
> seconds.
> 
> To avoid this ping-pong loop detect this situation and clamp the
> connector state to the old value.
> 
> Patch is inspired by a patch from Knut Peterson. Knut's patch
> completely ignored connector state changes if either the old or new
> status was unknown, which seemed to be a bit too agressive to me.
> 
> References: http://lists.freedesktop.org/archives/dri-devel/2012-August/025975.html
> Cc: Knut Petersen <Knut_Petersen at t-online.de>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Also Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

I don't think this has any effect for i915, the circumstances where it
might we return connector->status rather than Unknown, so we need some
input from nouveau/radeon/architect as to our sanity.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre