[Intel-gfx] [PATCH] drm/i915/lspcon: Switch back to PCON mode after output replug

[Imre Deak]

At least a ParadTech PS175 LSPCON chip/firmware uses long instead of
short pulses to signal output unplug/plug events. This is contrary to
how branch devices normally work which use short HPD signaling. This
chip will also switch to LS mode after an unplug event, which could be
the consequence of the long HPD signaling semantics and an effort to
save power automatically. Because of this we'll fail to do AUX and
detect the output after a replug event.

To fix this make sure we are in PCON mode during connector detection.

Cc: raptorteak at gmail.com
Cc: Shashank Sharma <shashank.sharma at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98912
Reported-and-tested-by: raptorteak at gmail.com
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 024798a..2a3ec20 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4270,12 +4270,16 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 static bool
 intel_dp_short_pulse(struct intel_dp *intel_dp)
 {
+	struct intel_lspcon *lspcon = dp_to_lspcon(intel_dp);
 	struct drm_device *dev = intel_dp_to_dev(intel_dp);
 	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
 	u8 sink_irq_vector = 0;
 	u8 old_sink_count = intel_dp->sink_count;
 	bool ret;
 
+	if (lspcon->active)
+		lspcon_resume(lspcon);
+
 	/*
 	 * Clearing compliance test variables to allow capturing
 	 * of values for next automated test request.
-- 
2.5.0