drm/i915: Iterate through the initialized DDIs to prepare their buffers

Not every DDIs is necessarily connected can be strapped off and, in the
future, we'll have platforms with a different number of default DDI
ports. So, let's only call intel_prepare_ddi_buffers() on DDI ports that
are actually detected.

We also use the opportunity to give a struct intel_digital_port to
intel_prepare_ddi_buffers() as we'll need it in a following patch to
query if the port supports HMDI or not.

On my HSW machine this removes the initialization of a couple of
(unused) DDIs.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -251,6 +251,10 @@ enum hpd_pin {
 			    &dev->mode_config.connector_list,	\
 			    base.head)
 
+#define for_each_digital_port(dev, digital_port)		\
+	list_for_each_entry(digital_port,			\
+			    &dev->mode_config.encoder_list,	\
+			    base.base.head)
 
 #define for_each_encoder_on_crtc(dev, __crtc, intel_encoder) \
 	list_for_each_entry((intel_encoder), &(dev)->mode_config.encoder_list, base.head) \

drivers/gpu/drm/i915/intel_ddi.c

@@ -198,10 +198,12 @@ enum port intel_ddi_get_encoder_port(struct intel_encoder *intel_encoder)
  * in either FDI or DP modes only, as HDMI connections will work with both
  * of those
  */
-static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
+static void intel_prepare_ddi_buffers(struct drm_device *dev,
+				      struct intel_digital_port *intel_dig_port)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	u32 reg;
+	int port = intel_dig_port->port;
 	int i, n_hdmi_entries, n_dp_entries, n_edp_entries, hdmi_default_entry,
 	    size;
 	int hdmi_level = dev_priv->vbt.ddi_port_info[port].hdmi_level_shift;
@@ -309,13 +311,19 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
  */
 void intel_prepare_ddi(struct drm_device *dev)
 {
-	int port;
+	struct intel_digital_port *intel_dig_port;
+	bool visited[I915_MAX_PORTS] = { 0, };
 
 	if (!HAS_DDI(dev))
 		return;
 
-	for (port = PORT_A; port <= PORT_E; port++)
-		intel_prepare_ddi_buffers(dev, port);
+	for_each_digital_port(dev, intel_dig_port) {
+		if (visited[intel_dig_port->port])
+			continue;
+
+		intel_prepare_ddi_buffers(dev, intel_dig_port);
+		visited[intel_dig_port->port] = true;
+	}
 }
 
 static void intel_wait_ddi_buf_idle(struct drm_i915_private *dev_priv,