From 42c51761cc82edbaa50d702a4614e179ad4bcd63 Mon Sep 17 00:00:00 2001
From: Fabian Vogt <fabian@ritter-vogt.de>
Date: Thu, 12 Nov 2020 20:30:55 +0100
Subject: [PATCH] Retry starting the display server

Even if the CanGraphical property of a Seat is true, it's possible that it's
still too early for X to start, as it might need some driver or device which
isn't present yet.

Fixes #1316
---
 src/daemon/Seat.cpp              | 23 ++++++++++++++++++-----
 src/daemon/Seat.h                |  4 +++-
 src/daemon/XorgDisplayServer.cpp | 10 ++++++----
 3 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/src/daemon/Seat.cpp b/src/daemon/Seat.cpp
index eef26da45..838c2221d 100644
--- a/src/daemon/Seat.cpp
+++ b/src/daemon/Seat.cpp
@@ -28,6 +28,7 @@
 
 #include <QDebug>
 #include <QFile>
+#include <QTimer>
 
 #include <functional>
 
@@ -52,7 +53,7 @@ namespace SDDM {
         return m_name;
     }
 
-    bool Seat::createDisplay(int terminalId) {
+    void Seat::createDisplay(int terminalId) {
         //reload config if needed
         mainConfig.load();
 
@@ -84,12 +85,24 @@ namespace SDDM {
         m_displays << display;
 
         // start the display
-        if (!display->start()) {
-            qCritical() << "Could not start Display server on vt" << terminalId;
-            return false;
+        startDisplay(display);
+    }
+
+    void Seat::startDisplay(Display *display, int tryNr) {
+        if (display->start())
+            return;
+
+        // It's possible that the system isn't ready yet (driver not loaded,
+        // device not enumerated, ...). It's not possible to tell when that changes,
+        // so try a few times with a delay in between.
+        qWarning() << "Attempt" << tryNr << "starting the Display server on vt" << display->terminalId() << "failed";
+
+        if(tryNr >= 3) {
+            qCritical() << "Could not start Display server on vt" << display->terminalId();
+            return;
         }
 
-        return true;
+        QTimer::singleShot(2000, display, [=] { startDisplay(display, tryNr + 1); });
     }
 
     void Seat::removeDisplay(Display* display) {
diff --git a/src/daemon/Seat.h b/src/daemon/Seat.h
index bf22566b7..f9fe7331f 100644
--- a/src/daemon/Seat.h
+++ b/src/daemon/Seat.h
@@ -35,13 +35,15 @@ namespace SDDM {
         const QString &name() const;
 
     public slots:
-        bool createDisplay(int terminalId = -1);
+        void createDisplay(int terminalId = -1);
         void removeDisplay(SDDM::Display* display);
 
     private slots:
         void displayStopped();
 
     private:
+        void startDisplay(SDDM::Display *display, int tryNr = 1);
+
         QString m_name;
 
         QVector<Display *> m_displays;
diff --git a/src/daemon/XorgDisplayServer.cpp b/src/daemon/XorgDisplayServer.cpp
index e60c02210..5f40fe8c3 100644
--- a/src/daemon/XorgDisplayServer.cpp
+++ b/src/daemon/XorgDisplayServer.cpp
@@ -248,6 +248,12 @@ namespace SDDM {
     }
 
     void XorgDisplayServer::finished() {
+        // clean up
+        if (process) {
+            process->deleteLater();
+            process = nullptr;
+        }
+
         // check flag
         if (!m_started)
             return;
@@ -283,10 +289,6 @@ namespace SDDM {
         displayStopScript->deleteLater();
         displayStopScript = nullptr;
 
-        // clean up
-        process->deleteLater();
-        process = nullptr;
-
         // remove authority file
         QFile::remove(m_authPath);