[Intel-gfx] [PATCH 2/3] drm/i915: Add HDMI probe function

[Sonika Jindal]

From: Shashank Sharma <contactshashanksharma at gmail.com>

This patch adds a separate probe function for HDMI
EDID read over DDC channel. This function has been
registered as a .hot_plug handler for HDMI encoder.

The reason behind addition of this separate function needs
brief explaination. The current implementation of hdmi_detect()
function re-sets the cached HDMI edid (in connector->detect_edid) in
every detect call.This function gets called many times, sometimes
directly from userspace probes, forcing drivers to read EDID every
detect function call.This causes several problems like:

1. Race conditions in multiple hot_plug / unplug cases, between
   interrupts bottom halves and userspace detections.
2. Many Un-necessary EDID reads for single hotplug/unplug
3. HDMI complaince failures which expects only one EDID read per hotplug

This function will be serving the purpose of really reading the EDID
by really probing the DDC channel, and updating the cached EDID.

The plan is to:
1. i915 IRQ handler bottom half function already calls
   intel_encoder->hotplug() function. Adding This probe function which
   will read the EDID only in case of a hotplug / unplug.
2. Reuse the cached EDID in hdmi_detect() function UNLESS we are forced
   to probe the EDID by the force=1 variable.The next patch in the
   series does this.
3. Make sure that we are using this force variable properly.

Signed-off-by: Shashank Sharma <contactshashanksharma at gmail.com>
---
 drivers/gpu/drm/i915/intel_hdmi.c |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index af4d1e6..064ddd8 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -1340,6 +1340,24 @@ intel_hdmi_set_edid(struct drm_connector *connector)
 	return connected;
 }
 
+void intel_hdmi_probe(struct intel_encoder *intel_encoder)
+{
+	struct intel_hdmi *intel_hdmi =
+			enc_to_intel_hdmi(&intel_encoder->base);
+	struct intel_connector *intel_connector =
+				intel_hdmi->attached_connector;
+	/*
+	 * We are here, means there is a hotplug or a force
+	 * detection. Clear the cached EDID and probe the
+	 * DDC bus to check the current status of HDMI.
+	 */
+	intel_hdmi_unset_edid(&intel_connector->base);
+	if (intel_hdmi_set_edid(&intel_connector->base))
+		DRM_DEBUG_DRIVER("DDC probe: got EDID\n");
+	else
+		DRM_DEBUG_DRIVER("DDC probe: no EDID\n");
+}
+
 static enum drm_connector_status
 intel_hdmi_detect(struct drm_connector *connector, bool force)
 {
@@ -1997,6 +2015,7 @@ void intel_hdmi_init_connector(struct intel_digital_port *intel_dig_port,
 	intel_connector->unregister = intel_connector_unregister;
 
 	intel_hdmi_add_properties(intel_hdmi, connector);
+	intel_encoder->hot_plug = intel_hdmi_probe;
 
 	intel_connector_attach_encoder(intel_connector, intel_encoder);
 	drm_connector_register(connector);
-- 
1.7.10.4