[Intel-gfx] [PATCH] drm/i915: Avoid fluctuating to UNKNOWN connector status during forced probes

[Chris Wilson]

On Mon, Jun 15, 2015 at 02:29:28PM +0200, Daniel Vetter wrote:
> On Fri, Jun 05, 2015 at 08:46:19AM +0100, Chris Wilson wrote:
> > For old-school component TV and CRT connectors, we require a heavyweight
> > load-detection mechanism. This involves setting up a CRTC and sending a
> > signal to the output, before reading back any response. As that is quite
> > slow and CPU heavy, the process is only performed when the output
> > detection is forced by user request. As it requires a driving CRTC, we
> > often don't have the resources to complete the probe. This leaves us in
> > a quandary where the unforced path just returns the old connector
> > status, but the forced detection path elects to return UNKNOWN. If we
> > have an active connection, we likely have the resources available to
> > complete the probe - but if it is currently disconnected, then it
> > becomes unknown and triggers a hotplug event, with often quite unfortunate
> > userspace behaviour (e.g. one output is blanked and the spurious TV
> > turned on).
> > 
> > To reduce spurious hotplug events on older devices, we can prevent
> > transitions between disconnected <-> unknown.
> > 
> > v2: Convert tv_type to use proper unknown enum (Ville)
> > 
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=87049
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com> [v1]
> > Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com> [v1]
> 
> This solution is at odds with
> 
> commit b7703726251191cd9f3ef3a80b2d9667901eec95
> Author: Daniel Vetter <daniel.vetter at ffwll.ch>
> Date:   Wed Jan 21 08:45:22 2015 +0100
> 
>     drm/probe-helper: clamp unknown connector status in the poll work
> 
> We're missing this bit of logic from the hotplug handlers, but that was
> somewhat intentional since a hotplug should indicate that something has
> changed. And in the i915 hpd handler we filter by source.
> 
> Given that the report is older than me having resurrect that patch can we
> close it as fixed or do I miss something?

It's a different path. This also concerns the actual forced reprobe
fluctuating between two states.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre