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drm/probe-helper: clamp unknown connector status in the poll work

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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.

v2: Rebased onto the drm_probe_helper.c extraction.

References: http://lists.freedesktop.org/archives/dri-devel/2012-August/025975.html
Cc: Knut Petersen <Knut_Petersen@t-online.de>
Cc: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Rob Clark <robdclark@gmail.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Daniel Vetter 2015-01-21 08:45:22 +01:00
parent 162b6a57ac
commit b770372625
1 changed files with 18 additions and 0 deletions
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18
drivers/gpu/drm/drm_probe_helper.c
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@ -335,6 +335,24 @@ static void output_poll_execute(struct work_struct *work)
if (old_status != connector->status) {
const char *old, *new;
/*
* The poll work sets force=false when calling detect so
* that drivers can avoid to do disruptive tests (e.g.
* when load detect cycles could cause flickering on
* other, running displays). This bears the risk that we
* flip-flop between unknown here in the poll work and
* the real state when userspace forces a full detect
* call after receiving a hotplug event due to this
* change.
*
* Hence clamp an unknown detect status to the old
* value.
*/
if (connector->status == connector_status_unknown) {
connector->status = old_status;
continue;
}
old = drm_get_connector_status_name(old_status);
new = drm_get_connector_status_name(connector->status);