Introduce VK_KHR_display support for i.MX8 devices

The eglfs_viv backend has Vulkan support now. While the support code is
common (lives in api/vulkan), we will not expose this for any other integration
yet, without the appropriate testing.

While putting this to eglfs seems unintuitive at first, it turns out that
for Vivante in particular this is very useful, since we can rely on the existing
framebuffer device infrastructure to solve certain problems (like the lack of
vsync)

The VK_KHR_display implementation of Vivante currently exhibits all the known issues
of the old, fbdev-style EGL plumbing (presumably since it lives on top of that):

- No vsync. This can be fixed by setting QT_QPA_EGLFS_FORCEVSYNC.

- May need a manual call to fbset to set the correct resolution before
launching the Qt app.

- And of course it lacks all the multi-screen features provided by drm.

- Plus, it seems the swapchain only supports a min/max buffer count of 1. This
needs special handling in QRhi since until now we assumed that there was always
at least 2 buffers available.

[ChangeLog][Platform Specific Changes][Linux] Vulkan is now supported by eglfs
(eglfs_viv backend) on i.MX8 devices with the Vivante graphics stack. This is done
via VK_KHR_display so no windowing system is required.

Task-number: QTBUG-78754
Change-Id: I7530aa026d4b904b9de83f9bdbdc4897ae770e71
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/plugins/platforms/eglfs/api/qeglfswindow_p.h b/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
index be2a0630d3..7bf74c25ee 100644
--- a/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
+++ b/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
@@ -64,6 +64,7 @@ QT_BEGIN_NAMESPACE
 
 class QOpenGLCompositorBackingStore;
 class QPlatformTextureList;
+
 #ifndef QT_NO_OPENGL
 class Q_EGLFS_EXPORT QEglFSWindow : public QPlatformWindow, public QOpenGLCompositorWindow
 #else
@@ -96,6 +97,9 @@ public:
     EGLNativeWindowType eglWindow() const;
     EGLSurface surface() const;
     QEglFSScreen *screen() const override;
+#if QT_CONFIG(vulkan)
+    virtual void *vulkanSurfacePtr() { return nullptr; }
+#endif
 
     bool hasNativeWindow() const { return m_flags.testFlag(HasNativeWindow); }