From 814a04927d54586ea478ba6ac14eb4fca5667239 Mon Sep 17 00:00:00 2001
From: Olivier Fourdan <ofourdan@redhat.com>
Date: Mon, 15 May 2023 09:23:57 +0200
Subject: [PATCH] xwayland: Keep the CVT timings for non-standard modes
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The current code, as changed by commit ad2d461de „Do not round
non-standard modes“ is reported to be logically incongruent.

We should either drop libxcvt entirely or simply fix the size, keeping
the CVT timings unchanged.

For backward compatibility and simplicity, I'd rather simply fix the
hdisplay/vdisplay to match the given size.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Fixes: ad2d461de - xwayland: Do not round non-standard modes
Closes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1549
---
 hw/xwayland/xwayland-cvt.c | 24 ++++++------------------
 1 file changed, 6 insertions(+), 18 deletions(-)

diff --git a/hw/xwayland/xwayland-cvt.c b/hw/xwayland/xwayland-cvt.c
index d052471eb..4248d3869 100644
--- a/hw/xwayland/xwayland-cvt.c
+++ b/hw/xwayland/xwayland-cvt.c
@@ -53,17 +53,6 @@ xwayland_modeinfo_from_cvt(xRRModeInfo *modeinfo,
     free(libxcvt_mode_info);
 }
 
-static void
-xwayland_modeinfo_from_values(xRRModeInfo *modeinfo,
-                              int hdisplay, int vdisplay, float vrefresh)
-{
-    modeinfo->width  = hdisplay;
-    modeinfo->height = vdisplay;
-    modeinfo->hTotal = hdisplay;
-    modeinfo->vTotal = vdisplay;
-    modeinfo->dotClock = hdisplay * vdisplay * vrefresh;
-}
-
 RRModePtr
 xwayland_cvt(int hdisplay, int vdisplay, float vrefresh, Bool reduced,
              Bool interlaced)
@@ -75,14 +64,13 @@ xwayland_cvt(int hdisplay, int vdisplay, float vrefresh, Bool reduced,
                                hdisplay, vdisplay, vrefresh, reduced, interlaced);
 
     /* Horizontal granularity in libxcvt is 8, so if our horizontal size is not
-     * divisible by 8, libxcvt will round it down, and we will advertise a wrong
-     * size to our XRandR clients. Fallback to a simpler method in that case.
+     * divisible by 8, libxcvt will round it up, and we will advertise a wrong
+     * size to our XRandR clients.
+     * Force the width/height (i.e. simply increase blanking which should not
+     * hurt anything), keeping the rest of the CVT mode timings unchanged.
      */
-    if (modeinfo.width != hdisplay || modeinfo.height != vdisplay) {
-        memset(&modeinfo, 0, sizeof(xRRModeInfo));
-        xwayland_modeinfo_from_values(&modeinfo,
-                                      hdisplay, vdisplay, vrefresh);
-    }
+    modeinfo.width = hdisplay;
+    modeinfo.height = vdisplay;
 
     snprintf(name, sizeof name, "%dx%d",
              modeinfo.width, modeinfo.height);