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From b3ac4f9295d36f14da53417d416afbcaf9146685 Mon Sep 17 00:00:00 2001
From: Piotr Wojnarowski <piotr@wojnarow.ski>
Date: Wed, 9 Sep 2026 23:39:47 +0200
Subject: [PATCH] backends/x11: Fix pixel clock overflow
XCB exposes dot_clock as uint32_t, and storing it in int overflows for
high-bandwidth modes. For example, 3840x2160 at 240 Hz has a dot clock
of 2332000000.
The resulting negative refresh rate wraps to 4294765262 mHz and creates
a zero-interval offscreen frame callback timer, making kwin_x11
consume an entire CPU core.
Use 64-bit arithmetic for the refresh-rate calculation.
BUG: 525454
---
src/backends/x11/standalone/x11_standalone_backend.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/backends/x11/standalone/x11_standalone_backend.cpp b/src/backends/x11/standalone/x11_standalone_backend.cpp
index 82baf4c0a3..415da7ab38 100644
--- a/src/backends/x11/standalone/x11_standalone_backend.cpp
+++ b/src/backends/x11/standalone/x11_standalone_backend.cpp
@@ -305,8 +305,8 @@ void X11StandaloneBackend::doUpdateOutputs()
if (info->mode == mode.id) {
if (mode.htotal != 0 && mode.vtotal != 0) { // BUG 313996
// refresh rate calculation - WTF was wikipedia 1998 when I needed it?
- int dotclock = mode.dot_clock,
- vtotal = mode.vtotal;
+ uint64_t dotclock = mode.dot_clock,
+ vtotal = mode.vtotal;
if (mode.mode_flags & XCB_RANDR_MODE_FLAG_INTERLACE) {
dotclock *= 2;
}
--
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