From 5bd48047de4abecc47187d938c5e6ed8b8304aaf Mon Sep 17 00:00:00 2001
From: Laszlo Agocs <laszlo.agocs@qt.io>
Date: Fri, 8 Nov 2019 11:41:16 +0100
Subject: 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>
---
 src/platformsupport/kmsconvenience/qkmsdevice.cpp | 58 +++++++++++++----------
 1 file changed, 33 insertions(+), 25 deletions(-)

(limited to 'src/platformsupport/kmsconvenience/qkmsdevice.cpp')

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
-- 
cgit v1.2.3