[PATCH] drm/i915/hdmi: Fix weak connector detection

[Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>]

Currently, our implementation of drm_connector_funcs.detect is
based on getting a valid EDID.

This requirement makes the driver fail to detect connected
connectors in case of EDID corruption, which prevents from falling
back to modes provided by builtin or user-provided EDIDs.

Let's fix this by improving the detection, with a DDC probe,
if the current EDID-based detection failed.

Note that a better way of dealing with this could calling
drm_probe_ddc in drm_connector_funcs.detect, and do the
EDID full reading and parsing in drm_connector_helper_funcs.get_modes,
when it's actually needed.

However, this would be more invasive and thus more error-prone.
The current commit is an attempt to get some uninvasive fix,
and allow for easier backporting.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
---
 drivers/gpu/drm/i915/intel_hdmi.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index a0d8daed2470..c079206e6681 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -1428,6 +1428,20 @@ intel_hdmi_detect(struct drm_connector *connector, bool force)
 	} else
 		status = connector_status_disconnected;
 
+	/*
+	 * The above call to intel_hdmi_set_edid() checked for a valid EDID.
+	 * However, the EDID can get corrupted for several reasons, resulting
+	 * in a disconnected status despite the connector being connected.
+	 * Hence, let's try one more time, by only probing the DDC.
+	 *
+	 * This allows the DRM core to fallback to builtin or user-provided
+	 * EDID firmware, e.g. in drm_helper_probe_single_connector_modes.
+	 */
+	if (status == connector_status_disconnected)
+		if (drm_probe_ddc(intel_gmbus_get_adapter(dev_priv,
+						intel_hdmi->ddc_bus)))
+			status = connector_status_connected;
+
 	intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
 
 	return status;
-- 
2.7.0

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