From 869e86ff0014e020c4076a8f22e78f69cab1063a Mon Sep 17 00:00:00 2001
From: Xaver Hugl <xaver.hugl@gmail.com>
Date: Mon, 13 Nov 2023 14:46:26 +0100
Subject: [PATCH] backends/drm: disable buffer readability checks on Intel

They cause stutters and reduced frame rates on some Intel laptops because the
buffers don't become readable in time, so disable the checks until that's fixed
on the driver side. For debugging purposes, the environment variable
KWIN_DRM_DISABLE_BUFFER_READABILITY_CHECKS can be used to override the default
behavior.

BUG: 476860
---
 src/backends/drm/drm_buffer.cpp | 8 ++++++++
 src/backends/drm/drm_gpu.cpp    | 6 ++++++
 src/backends/drm/drm_gpu.h      | 2 ++
 3 files changed, 16 insertions(+)

diff --git a/src/backends/drm/drm_buffer.cpp b/src/backends/drm/drm_buffer.cpp
index 0f0b8b71f4..ea097232a9 100644
--- a/src/backends/drm/drm_buffer.cpp
+++ b/src/backends/drm/drm_buffer.cpp
@@ -26,11 +26,19 @@
 namespace KWin
 {
 
+static bool s_envIsSet = false;
+static bool s_disableBufferWait = qEnvironmentVariableIntValue("KWIN_DRM_DISABLE_BUFFER_READABILITY_CHECKS", &s_envIsSet) && s_envIsSet;
+
 DrmFramebuffer::DrmFramebuffer(DrmGpu *gpu, uint32_t fbId, GraphicsBuffer *buffer)
     : m_framebufferId(fbId)
     , m_gpu(gpu)
     , m_bufferRef(buffer)
 {
+    if (s_disableBufferWait || (m_gpu->isI915() && !s_envIsSet)) {
+        // buffer readability checks cause frames to be wrongly delayed on some Intel laptops
+        // See https://gitlab.freedesktop.org/drm/intel/-/issues/9415
+        m_readable = true;
+    }
 }
 
 DrmFramebuffer::~DrmFramebuffer()
diff --git a/src/backends/drm/drm_gpu.cpp b/src/backends/drm/drm_gpu.cpp
index b83f5d7d21..e2dcf8c41b 100644
--- a/src/backends/drm/drm_gpu.cpp
+++ b/src/backends/drm/drm_gpu.cpp
@@ -75,6 +75,7 @@ DrmGpu::DrmGpu(DrmBackend *backend, const QString &devNode, int fd, dev_t device
     // find out what driver this kms device is using
     DrmUniquePtr<drmVersion> version(drmGetVersion(fd));
     m_isNVidia = strstr(version->name, "nvidia-drm");
+    m_isI915 = strstr(version->name, "i915");
     m_isVirtualMachine = strstr(version->name, "virtio") || strstr(version->name, "qxl")
         || strstr(version->name, "vmwgfx") || strstr(version->name, "vboxvideo");
 
@@ -690,6 +691,11 @@ bool DrmGpu::isNVidia() const
     return m_isNVidia;
 }
 
+bool DrmGpu::isI915() const
+{
+    return m_isI915;
+}
+
 bool DrmGpu::isRemoved() const
 {
     return m_isRemoved;
diff --git a/src/backends/drm/drm_gpu.h b/src/backends/drm/drm_gpu.h
index 27e546eea5..d91f8cad81 100644
--- a/src/backends/drm/drm_gpu.h
+++ b/src/backends/drm/drm_gpu.h
@@ -79,6 +79,7 @@ public:
     bool addFB2ModifiersSupported() const;
     bool asyncPageflipSupported() const;
     bool isNVidia() const;
+    bool isI915() const;
     gbm_device *gbmDevice() const;
     EglDisplay *eglDisplay() const;
     DrmBackend *platform() const;
@@ -137,6 +138,7 @@ private:
     bool m_atomicModeSetting;
     bool m_addFB2ModifiersSupported = false;
     bool m_isNVidia;
+    bool m_isI915;
     bool m_isVirtualMachine;
     bool m_asyncPageflipSupported = false;
     bool m_isRemoved = false;