drm/i915: Remove DDC pin sanitation

Stop with the VBT DDC pin sanitation, and instead just check
that the appropriate DDC pin is still available when initializing
a HDMI connector.

The reason being that we want to start initializing ports in
VBT order to deal with VBTs that declare child devices with
seemingly conflicting ports. As the encoder initialization can
fail for other reasons (at least for eDP+AUX) we can't know
upfront which way the conflicts should be resolved.

Note that the old way of sanitizing gave priority to the last
port declared in the VBT, but now we sort of do the opposite by
favoring the first encoder to successfully initialize. So far
we're not aware of HDMI/DDC use cases where this would matter
but for AUX CH (will be subject to a similar change) there are
known cases where it matters.

Also note that the old code fell back to the platform default DDC
pin if the VBT pin was populated but invalid. That doesn't seem like
such a great idea because the VBT might have later declared another
port using that platform default pin, and so we might just be
creating more DDC pin conflicts here. So lets not second guess the
VBT and simply reject the entire HDMI encoder if the VBT DDC pin is
invalid.

v2: Pimp the commit message (Jani)

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230630155846.29931-4-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 59 insertions, 13 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index 7ac5e6c5e00dc..8d1c8abfcffa1 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -2880,21 +2880,12 @@ static u8 g4x_port_to_ddc_pin(struct drm_i915_private *dev_priv,
 	return ddc_pin;
 }
 
-static u8 intel_hdmi_ddc_pin(struct intel_encoder *encoder)
+static u8 intel_hdmi_default_ddc_pin(struct intel_encoder *encoder)
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 	enum port port = encoder->port;
 	u8 ddc_pin;
 
-	ddc_pin = intel_bios_hdmi_ddc_pin(encoder->devdata);
-	if (ddc_pin) {
-		drm_dbg_kms(&dev_priv->drm,
-			    "[ENCODER:%d:%s] Using DDC pin 0x%x (VBT)\n",
-			    encoder->base.base.id, encoder->base.name,
-			    ddc_pin);
-		return ddc_pin;
-	}
-
 	if (IS_ALDERLAKE_S(dev_priv))
 		ddc_pin = adls_port_to_ddc_pin(dev_priv, port);
 	else if (INTEL_PCH_TYPE(dev_priv) >= PCH_DG1)
@@ -2916,10 +2907,62 @@ static u8 intel_hdmi_ddc_pin(struct intel_encoder *encoder)
 	else
 		ddc_pin = g4x_port_to_ddc_pin(dev_priv, port);
 
-	drm_dbg_kms(&dev_priv->drm,
-		    "[ENCODER:%d:%s] Using DDC pin 0x%x (platform default)\n",
+	return ddc_pin;
+}
+
+static struct intel_encoder *
+get_encoder_by_ddc_pin(struct intel_encoder *encoder, u8 ddc_pin)
+{
+	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
+	struct intel_encoder *other;
+
+	for_each_intel_encoder(&i915->drm, other) {
+		if (other == encoder)
+			continue;
+
+		if (!intel_encoder_is_dig_port(other))
+			continue;
+
+		if (enc_to_dig_port(other)->hdmi.ddc_bus == ddc_pin)
+			return other;
+	}
+
+	return NULL;
+}
+
+static u8 intel_hdmi_ddc_pin(struct intel_encoder *encoder)
+{
+	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
+	struct intel_encoder *other;
+	const char *source;
+	u8 ddc_pin;
+
+	ddc_pin = intel_bios_hdmi_ddc_pin(encoder->devdata);
+	source = "VBT";
+
+	if (!ddc_pin) {
+		ddc_pin = intel_hdmi_default_ddc_pin(encoder);
+		source = "platform default";
+	}
+
+	if (!intel_gmbus_is_valid_pin(i915, ddc_pin)) {
+		drm_dbg_kms(&i915->drm, "[ENCODER:%d:%s] Invalid DDC pin %d\n",
+			    encoder->base.base.id, encoder->base.name, ddc_pin);
+		return 0;
+	}
+
+	other = get_encoder_by_ddc_pin(encoder, ddc_pin);
+	if (other) {
+		drm_dbg_kms(&i915->drm, "[ENCODER:%d:%s] DDC pin %d already claimed by [ENCODER:%d:%s]\n",
+			    encoder->base.base.id, encoder->base.name, ddc_pin,
+			    other->base.base.id, other->base.name);
+		return 0;
+	}
+
+	drm_dbg_kms(&i915->drm,
+		    "[ENCODER:%d:%s] Using DDC pin 0x%x (%s)\n",
 		    encoder->base.base.id, encoder->base.name,
-		    ddc_pin);
+		    ddc_pin, source);
 
 	return ddc_pin;
 }
@@ -2990,6 +3033,9 @@ void intel_hdmi_init_connector(struct intel_digital_port *dig_port,
 		return;
 
 	intel_hdmi->ddc_bus = intel_hdmi_ddc_pin(intel_encoder);
+	if (!intel_hdmi->ddc_bus)
+		return;
+
 	ddc = intel_gmbus_get_adapter(dev_priv, intel_hdmi->ddc_bus);
 
 	drm_connector_init_with_ddc(dev, connector,