[PATCH 2/2] drm/i915: Enable hotplug retry

[José Roberto de Souza]

Right now we are aware of two cases that needs another hotplug retry:
- Unpowered type-c dongles
- HDMI slow unplug

Both have a complete explanation in the code to schedule another run
of the hotplug handler.

It could have more checks to just trigger the retry in those two
specific cases but why would sink signal a long pulse if there is
no change? Also the drawback of running the hotplug handler again
is really low and that could fix another cases that we are not
aware.

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Imre Deak <imre.deak at intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
---
 drivers/gpu/drm/i915/intel_ddi.c  | 21 +++++++++++++++++++++
 drivers/gpu/drm/i915/intel_hdmi.c | 28 +++++++++++++++++++++++++++-
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 08ef5befe094..7a5e2eb3e756 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -4071,6 +4071,7 @@ intel_ddi_hotplug(struct intel_encoder *encoder,
 		  struct intel_connector *connector,
 		  bool irq_received)
 {
+	struct intel_digital_port *dig_port = enc_to_dig_port(&encoder->base);
 	struct drm_modeset_acquire_ctx ctx;
 	enum intel_hotplug_state state;
 	int ret;
@@ -4097,6 +4098,26 @@ intel_ddi_hotplug(struct intel_encoder *encoder,
 	drm_modeset_acquire_fini(&ctx);
 	WARN(ret, "Acquiring modeset locks failed with %i\n", ret);
 
+	/*
+	 * Unpowered type-c dongles can take some time to boot and be
+	 * responsible, so here giving some time to those dongles to power up
+	 * and then retrying the probe.
+	 *
+	 * On many platforms the HDMI live state signal is known to be
+	 * unreliable, so we can't use it to detect if a sink is connected or
+	 * not. Instead we detect if it's connected based on whether we can
+	 * read the EDID or not. That in turn has a problem during disconnect,
+	 * since the HPD interrupt may be raised before the DDC lines get
+	 * disconnected (due to how the required length of DDC vs. HPD
+	 * connector pins are specified) and so we'll still be able to get a
+	 * valid EDID. To solve this schedule another detection cycle if this
+	 * time around we didn't detect any change in the sink's connection
+	 * status.
+	 */
+	if (state == INTEL_HOTPLUG_NOCHANGE && irq_received &&
+	    !dig_port->dp.is_mst)
+		state = INTEL_HOTPLUG_RETRY;
+
 	return state;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index cd422a7b4da0..365705e81f58 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -3025,6 +3025,32 @@ void intel_hdmi_init_connector(struct intel_digital_port *intel_dig_port,
 		DRM_DEBUG_KMS("CEC notifier get failed\n");
 }
 
+static enum intel_hotplug_state
+intel_hdmi_hotplug(struct intel_encoder *encoder,
+		   struct intel_connector *connector, bool irq_received)
+{
+	enum intel_hotplug_state state;
+
+	state = intel_encoder_hotplug(encoder, connector, irq_received);
+
+	/*
+	 * On many platforms the HDMI live state signal is known to be
+	 * unreliable, so we can't use it to detect if a sink is connected or
+	 * not. Instead we detect if it's connected based on whether we can
+	 * read the EDID or not. That in turn has a problem during disconnect,
+	 * since the HPD interrupt may be raised before the DDC lines get
+	 * disconnected (due to how the required length of DDC vs. HPD
+	 * connector pins are specified) and so we'll still be able to get a
+	 * valid EDID. To solve this schedule another detection cycle if this
+	 * time around we didn't detect any change in the sink's connection
+	 * status.
+	 */
+	if (state == INTEL_HOTPLUG_NOCHANGE && irq_received)
+		state = INTEL_HOTPLUG_RETRY;
+
+	return state;
+}
+
 void intel_hdmi_init(struct drm_i915_private *dev_priv,
 		     i915_reg_t hdmi_reg, enum port port)
 {
@@ -3048,7 +3074,7 @@ void intel_hdmi_init(struct drm_i915_private *dev_priv,
 			 &intel_hdmi_enc_funcs, DRM_MODE_ENCODER_TMDS,
 			 "HDMI %c", port_name(port));
 
-	intel_encoder->hotplug = intel_encoder_hotplug;
+	intel_encoder->hotplug = intel_hdmi_hotplug;
 	intel_encoder->compute_config = intel_hdmi_compute_config;
 	if (HAS_PCH_SPLIT(dev_priv)) {
 		intel_encoder->disable = pch_disable_hdmi;
-- 
2.21.0