intel_extreme: fix assigning pipes to displays

The previous code did not handle correctly the case where a display
requested a fixed mapping, and cloud end up assigning the same pipe to
multiple displays. But we want a separate pipe for each display,
allowing multihead support later on.

Rewrite the algorithm to first assign pipes to devices with fixed
constraints, and in a second pass assing the remaining pipes to other
displays.

src/add-ons/accelerants/intel_extreme/accelerant.cpp

@@ -433,20 +433,36 @@ assign_pipes()
 	// assigned when the count is > 1;
 
 	uint32 current = 0;
+
+	bool assigned[gInfo->pipe_count];
+	memset(assigned, 0, gInfo->pipe_count);
+
+	// Some ports need to be assigned to a fixed pipe on old hardware (or due
+	// to limitations in the current driver on current hardware). Assign those
+	// first
 	for (uint32 i = 0; i < gInfo->port_count; i++) {
 		if (gInfo->ports[i] == NULL)
 			continue;
 
 		pipe_index preference = gInfo->ports[i]->PipePreference();
 		if (preference != INTEL_PIPE_ANY) {
-			// Some ports *really* need to be assigned a pipe due to
-			// implementation bugs.
 			int index = (preference == INTEL_PIPE_B) ? 1 : 0;
+			if (assigned[index]) {
+				TRACE("Pipe %d is already assigned, it will drive multiple "
+					"displays\n", index);
+			}
 			gInfo->ports[i]->SetPipe(gInfo->pipes[index]);
+			assigned[index] = true;
 			continue;
 		}
+	}
 
+	// In a second pass, assign the remaining ports to the remaining pipes
+	for (uint32 i = 0; i < gInfo->port_count; i++) {
 		if (gInfo->ports[i]->IsConnected()) {
+			while (current < gInfo->pipe_count && assigned[current])
+				current++;
+
 			if (current >= gInfo->pipe_count) {
 				ERROR("%s: No pipes left to assign to port %s!\n", __func__,
 					gInfo->ports[i]->PortName());
@@ -454,7 +470,6 @@ assign_pipes()
 			}
 
 			gInfo->ports[i]->SetPipe(gInfo->pipes[current]);
-			current++;
 		}
 	}