eglfs: kms: Make threaded atomic drm work

The atomic modesetting support was not prepared for page flips being
issued from different (per-screen) threads.

This could be seen with the threaded render loop of Qt Quick: having a
QQuickWindow per screen means having a dedicated render thread for each
screen. QKmsDevice used simply instance variables to keep track of the
request. This leads to the commit failing with EBUSY sooner or later.

Make the atomic request and related variables thread local.

This prevents failing drmModeAtomicCommit() with 2 or more screens and
the threaded render loop. It does not fix other potential issues when
waiting for page flips to complete, that is to be tackled separately.

Task-number: QTBUG-74953
Change-Id: I2dac10d5e9bdc0cb556ac78c9643c96d40d692e4
Reviewed-by: Johan Helsing <johan.helsing@qt.io>

4 files changed, 50 insertions, 41 deletions

diff --git a/src/platformsupport/kmsconvenience/qkmsdevice.cpp b/src/platformsupport/kmsconvenience/qkmsdevice.cpp
index 90437117aa..92ba9fbcd9 100644
--- a/src/platformsupport/kmsconvenience/qkmsdevice.cpp
+++ b/src/platformsupport/kmsconvenience/qkmsdevice.cpp
@@ -581,10 +581,6 @@ QKmsDevice::QKmsDevice(QKmsScreenConfig *screenConfig, const QString &path)
     , m_path(path)
     , m_dri_fd(-1)
     , m_has_atomic_support(false)
-#if QT_CONFIG(drm_atomic)
-    , m_atomic_request(nullptr)
-    , m_previous_request(nullptr)
-#endif
     , m_crtc_allocator(0)
 {
     if (m_path.isEmpty()) {
@@ -600,7 +596,7 @@ QKmsDevice::QKmsDevice(QKmsScreenConfig *screenConfig, const QString &path)
 QKmsDevice::~QKmsDevice()
 {
 #if QT_CONFIG(drm_atomic)
-    atomicReset();
+    threadLocalAtomicReset();
 #endif
 }
 
@@ -940,39 +936,51 @@ bool QKmsDevice::hasAtomicSupport()
 }
 
 #if QT_CONFIG(drm_atomic)
-drmModeAtomicReq * QKmsDevice::atomic_request()
+drmModeAtomicReq *QKmsDevice::threadLocalAtomicRequest()
 {
-    if (!m_atomic_request && m_has_atomic_support)
-        m_atomic_request = drmModeAtomicAlloc();
+    if (!m_has_atomic_support)
+        return nullptr;
 
-    return m_atomic_request;
+    AtomicReqs &a(m_atomicReqs.localData());
+    if (!a.request)
+        a.request = drmModeAtomicAlloc();
+
+    return a.request;
 }
 
-bool QKmsDevice::atomicCommit(void *user_data)
+bool QKmsDevice::threadLocalAtomicCommit(void *user_data)
 {
-    if (m_atomic_request) {
-        int ret = drmModeAtomicCommit(m_dri_fd, m_atomic_request,
-                          DRM_MODE_ATOMIC_NONBLOCK | DRM_MODE_PAGE_FLIP_EVENT | DRM_MODE_ATOMIC_ALLOW_MODESET, user_data);
+    if (!m_has_atomic_support)
+        return false;
 
-        if (ret) {
-           qWarning("Failed to commit atomic request (code=%d)", ret);
-           return false;
-        }
+    AtomicReqs &a(m_atomicReqs.localData());
+    if (!a.request)
+        return false;
 
-        m_previous_request = m_atomic_request;
-        m_atomic_request = nullptr;
+    int ret = drmModeAtomicCommit(m_dri_fd, a.request,
+                                  DRM_MODE_ATOMIC_NONBLOCK | DRM_MODE_PAGE_FLIP_EVENT | DRM_MODE_ATOMIC_ALLOW_MODESET,
+                                  user_data);
 
-        return true;
+    if (ret) {
+        qWarning("Failed to commit atomic request (code=%d)", ret);
+        return false;
     }
 
-    return false;
+    a.previous_request = a.request;
+    a.request = nullptr;
+
+    return true;
 }
 
-void QKmsDevice::atomicReset()
+void QKmsDevice::threadLocalAtomicReset()
 {
-    if (m_previous_request) {
-        drmModeAtomicFree(m_previous_request);
-        m_previous_request = nullptr;
+    if (!m_has_atomic_support)
+        return;
+
+    AtomicReqs &a(m_atomicReqs.localData());
+    if (a.previous_request) {
+        drmModeAtomicFree(a.previous_request);
+        a.previous_request = nullptr;
     }
 }
 #endif
diff --git a/src/platformsupport/kmsconvenience/qkmsdevice_p.h b/src/platformsupport/kmsconvenience/qkmsdevice_p.h
index 0873154459..55a590cfce 100644
--- a/src/platformsupport/kmsconvenience/qkmsdevice_p.h
+++ b/src/platformsupport/kmsconvenience/qkmsdevice_p.h
@@ -57,6 +57,7 @@
 #include <qpa/qplatformscreen.h>
 #include <QtCore/QMap>
 #include <QtCore/QVariant>
+#include <QtCore/QThreadStorage>
 
 #include <xf86drm.h>
 #include <xf86drmMode.h>
@@ -241,10 +242,9 @@ public:
     bool hasAtomicSupport();
 
 #if QT_CONFIG(drm_atomic)
-    bool atomicCommit(void *user_data);
-    void atomicReset();
-
-    drmModeAtomicReq *atomic_request();
+    drmModeAtomicReq *threadLocalAtomicRequest();
+    bool threadLocalAtomicCommit(void *user_data);
+    void threadLocalAtomicReset();
 #endif
     void createScreens();
 
@@ -284,8 +284,11 @@ protected:
     bool m_has_atomic_support;
 
 #if QT_CONFIG(drm_atomic)
-    drmModeAtomicReq *m_atomic_request;
-    drmModeAtomicReq *m_previous_request;
+    struct AtomicReqs {
+        drmModeAtomicReq *request = nullptr;
+        drmModeAtomicReq *previous_request = nullptr;
+    };
+    QThreadStorage<AtomicReqs> m_atomicReqs;
 #endif
     quint32 m_crtc_allocator;
 
diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmscreen.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmscreen.cpp
index 16dbfe1522..333433f666 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmscreen.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms/qeglfskmsgbmscreen.cpp
@@ -243,7 +243,7 @@ void QEglFSKmsGbmScreen::ensureModeSet(uint32_t fb)
 
             if (device()->hasAtomicSupport()) {
 #if QT_CONFIG(drm_atomic)
-                drmModeAtomicReq *request = device()->atomic_request();
+                drmModeAtomicReq *request = device()->threadLocalAtomicRequest();
                 if (request) {
                     drmModeAtomicAddProperty(request, op.connector_id, op.crtcIdPropertyId, op.crtc_id);
                     drmModeAtomicAddProperty(request, op.crtc_id, op.modeIdPropertyId, op.mode_blob_id);
@@ -287,8 +287,7 @@ void QEglFSKmsGbmScreen::waitForFlip()
     }
 
 #if QT_CONFIG(drm_atomic)
-    if (device()->hasAtomicSupport())
-        device()->atomicReset();
+    device()->threadLocalAtomicReset();
 #endif
 }
 
@@ -324,16 +323,16 @@ void QEglFSKmsGbmScreen::flip()
 
     if (device()->hasAtomicSupport()) {
 #if QT_CONFIG(drm_atomic)
-        drmModeAtomicReq *request = device()->atomic_request();
+        drmModeAtomicReq *request = device()->threadLocalAtomicRequest();
         if (request) {
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->framebufferPropertyId, fb->fb);
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->crtcPropertyId, op.crtc_id);
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->srcwidthPropertyId,
-                                     output().size.width() << 16);
+                                     op.size.width() << 16);
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->srcXPropertyId, 0);
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->srcYPropertyId, 0);
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->srcheightPropertyId,
-                                     output().size.height() << 16);
+                                     op.size.height() << 16);
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->crtcXPropertyId, 0);
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->crtcYPropertyId, 0);
             drmModeAtomicAddProperty(request, op.eglfs_plane->id, op.eglfs_plane->crtcwidthPropertyId,
@@ -371,7 +370,7 @@ void QEglFSKmsGbmScreen::flip()
 
             if (device()->hasAtomicSupport()) {
 #if QT_CONFIG(drm_atomic)
-                drmModeAtomicReq *request = device()->atomic_request();
+                drmModeAtomicReq *request = device()->threadLocalAtomicRequest();
                 if (request) {
                     drmModeAtomicAddProperty(request, d.screen->output().eglfs_plane->id,
                                                       d.screen->output().eglfs_plane->framebufferPropertyId, fb->fb);
@@ -394,8 +393,7 @@ void QEglFSKmsGbmScreen::flip()
     }
 
 #if QT_CONFIG(drm_atomic)
-    if (device()->hasAtomicSupport())
-         device()->atomicCommit(this);
+    device()->threadLocalAtomicCommit(this);
 #endif
 }
 
diff --git a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsintegration.cpp b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsintegration.cpp
index a6aac61506..28b6b7df63 100644
--- a/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsintegration.cpp
+++ b/src/plugins/platforms/eglfs/deviceintegration/eglfs_kms_support/qeglfskmsintegration.cpp
@@ -140,7 +140,7 @@ void *QEglFSKmsIntegration::nativeResourceForIntegration(const QByteArray &name)
 
 #if QT_CONFIG(drm_atomic)
     if (name == QByteArrayLiteral("dri_atomic_request") && m_device)
-        return (void *) (qintptr) m_device->atomic_request();
+        return (void *) (qintptr) m_device->threadLocalAtomicRequest();
 #endif
     return nullptr;
 }