eglfs: allow forcing an explicit connector index on DRM/KMS

Add a QT_QPA_EGLFS_KMS_CONNECTOR_INDEX environment variable that applies
both to the GBM and EGLDevice backends. Instead of specifying all
uninteresting outputs as "off" in the config file in QT_QPA_EGLFS_KMS_CONFIG,
this variable provides a shortcut to force one single connector and ignore
all others in embedded systems with a fixed connector configuration. The index
must be between 0 and DRM connector count - 1.

Task-number: QTBUG-57386
Change-Id: I3f9562f48bf6b2ffaf9a0cc232e09a7e0c15645b
Reviewed-by: Pasi Petäjäjärvi <pasi.petajajarvi@qt.io>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsdevice.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsdevice.cpp
index f6b58d1ba6..b3c1fbb1bd 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsdevice.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsdevice.cpp
@@ -399,7 +399,20 @@ void QEglFSKmsDevice::createScreens()
 
     QVector<OrderedScreen> screens;
 
+    int wantedConnectorIndex = -1;
+    bool ok;
+    int idx = qEnvironmentVariableIntValue("QT_QPA_EGLFS_KMS_CONNECTOR_INDEX", &ok);
+    if (ok) {
+        if (idx >= 0 && idx < resources->count_connectors)
+            wantedConnectorIndex = idx;
+        else
+            qWarning("Invalid connector index %d", idx);
+    }
+
     for (int i = 0; i < resources->count_connectors; i++) {
+        if (wantedConnectorIndex >= 0 && i != wantedConnectorIndex)
+            continue;
+
         drmModeConnectorPtr connector = drmModeGetConnector(m_dri_fd, resources->connectors[i]);
         if (!connector)
             continue;