Enhancements to initialization code in drm backend (#344)

* Check if drm_crtc is nullptr before attempting to set mode

In native_window_drm, there's no check against null drm_crtc. So if
drm_crtc is null, and SwapBuffers() is called, a Segmentation Fault
will occur. This adds check against it.

Signed-off-by: Yunhao Tian <[email protected]>

* Add logic to initialize drm encoder and crtc

In RK3399 board, when the system just booted up, there's no encoder
attached to connector, and no crtc attached to encoder. In this case
drm backend will fail to get an encoder. This commit adds code to
find suitable encoder and crtc from resources, when absent.

Signed-off-by: Yunhao Tian <[email protected]>

* Add myself to AUTHORS

---------

Signed-off-by: Yunhao Tian <[email protected]>

Author: t123yh

AUTHORS

@@ -10,3 +10,4 @@ Andrea Daoud ([email protected])
 Valentin Hăloiu ([email protected])
 FlafyDev <[email protected]>
 Makoto Sato ([email protected])
+Yunhao Tian ([email protected])

src/flutter/shell/platform/linux_embedded/window/native_window_drm.cc

@@ -77,8 +77,18 @@ bool NativeWindowDrm::ConfigureDisplay(const uint16_t rotation) {
     drmModeFreeResources(resources);
     return false;
   }
-  if (encoder->crtc_id) {
-    drm_crtc_ = drmModeGetCrtc(drm_device_, encoder->crtc_id);
+  if (!encoder->crtc_id) {
+    // if there is no current CRTC, make sure to attach a suitable one
+    for (int c = 0; c < resources->count_crtcs; c++) {
+      if (encoder->possible_crtcs & (1 << c)) {
+        encoder->crtc_id = resources->crtcs[c];
+        break;
+      }
+    }
+  }
+  drm_crtc_ = drmModeGetCrtc(drm_device_, encoder->crtc_id);
+  if (!drm_crtc_) {
+    ELINUX_LOG(WARNING) << "Couldn't find a suitable crtc";
   }
 
   drmModeFreeEncoder(encoder);
@@ -103,11 +113,44 @@ drmModeConnectorPtr NativeWindowDrm::FindConnector(drmModeResPtr resources) {
 
 drmModeEncoder* NativeWindowDrm::FindEncoder(drmModeRes* resources,
                                              drmModeConnector* connector) {
-  if (connector->encoder_id) {
-    return drmModeGetEncoder(drm_device_, connector->encoder_id);
+  drmModeEncoder* encoder = nullptr;
+  // Find a suitable encoder
+  for (int e = 0; e < resources->count_encoders; e++) {
+    bool found = false;
+    encoder = drmModeGetEncoder(drm_device_, resources->encoders[e]);
+    for (int ce = 0; ce < connector->count_encoders; ce++) {
+      if (encoder && encoder->encoder_id == connector->encoders[ce]) {
+        ELINUX_LOG(DEBUG) << "Using encoder id " << encoder->encoder_id;
+        found = true;
+        break;
+      }
+    }
+    if (found)
+      break;
+    drmModeFreeEncoder(encoder);
+    encoder = nullptr;
   }
-  // no encoder found
-  return nullptr;
+
+  // If encoder is not connected to the connector,
+  // try to find a suitable one
+  if (!encoder) {
+    for (int e = 0; e < connector->count_encoders; e++) {
+      encoder = drmModeGetEncoder(drm_device_, connector->encoders[e]);
+      for (int c = 0; c < resources->count_crtcs; c++) {
+        if (encoder->possible_crtcs & (1 << c)) {
+          encoder->crtc_id = resources->crtcs[c];
+          break;
+        }
+      }
+      if (encoder->crtc_id)
+        break;
+      drmModeFreeEncoder(encoder);
+      encoder = nullptr;
+    }
+  }
+
+  // Will return nullptr if a suitable encoder is still not found
+  return encoder;
 }
 
 const uint32_t* NativeWindowDrm::GetCursorData(const std::string& cursor_name) {

src/flutter/shell/platform/linux_embedded/window/native_window_drm_gbm.cc

@@ -175,10 +175,14 @@ void NativeWindowDrmGbm::SwapBuffers() {
   if (result != 0) {
     ELINUX_LOG(ERROR) << "Failed to add a framebuffer. (" << result << ")";
   }
-  result = drmModeSetCrtc(drm_device_, drm_crtc_->crtc_id, fb, 0, 0,
-                          &drm_connector_id_, 1, &drm_mode_info_);
-  if (result != 0) {
-    ELINUX_LOG(ERROR) << "Failed to set crct mode. (" << result << ")";
+  if (!drm_crtc_) {
+    ELINUX_LOG(ERROR) << "crtc is null, cannot set mode.";
+  } else {
+    result = drmModeSetCrtc(drm_device_, drm_crtc_->crtc_id, fb, 0, 0,
+                            &drm_connector_id_, 1, &drm_mode_info_);
+    if (result != 0) {
+      ELINUX_LOG(ERROR) << "Failed to set crct mode. (" << result << ")";
+    }
   }
 
   if (gbm_previous_bo_) {