hw/xfree86: re-calculate the clock and refresh rate

xserver fails to generate useable resolutions with 90Hz framerate
panels(encounter the same issue with 3 different 2.5k resolution
panels). All the resolutions shown by xrandr lead to blank screen except
the one written in EDID.
Ville Syrjälä from Intel provides a method to calculate the preferred
clock and refresh rate from the existing resolution table and this
works for the issue.

v2. xf86ModeVRefresh might return 0, need to check it before use it.
v3. reported by Markus on launchpad that the issue is not devided by 0,
it's the "preferred" being accessed unconditionally.
BugLink: https://launchpad.net/bugs/1999852

Closes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1388
Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>

hw/xfree86/common/xf86Mode.c

@@ -230,6 +230,8 @@ xf86ModeStatusToString(ModeStatus status)
         return "monitor doesn't support reduced blanking";
     case MODE_BANDWIDTH:
         return "mode requires too much memory bandwidth";
+    case MODE_DUPLICATE:
+        return "the same mode has been added";
     case MODE_BAD:
         return "unknown reason";
     case MODE_ERROR:

hw/xfree86/drivers/modesetting/drmmode_display.c

@@ -2843,7 +2843,7 @@ static DisplayModePtr
 drmmode_output_add_gtf_modes(xf86OutputPtr output, DisplayModePtr Modes)
 {
     xf86MonPtr mon = output->MonInfo;
-    DisplayModePtr i, m, preferred = NULL;
+    DisplayModePtr i, j, m, preferred = NULL;
     int max_x = 0, max_y = 0;
     float max_vrefresh = 0.0;
 
@@ -2875,6 +2875,17 @@ drmmode_output_add_gtf_modes(xf86OutputPtr output, DisplayModePtr Modes)
             i->VDisplay >= preferred->VDisplay &&
             xf86ModeVRefresh(i) >= xf86ModeVRefresh(preferred))
             i->status = MODE_VSYNC;
+        if (preferred && xf86ModeVRefresh(i) > 0.0) {
+            i->Clock = i->Clock * xf86ModeVRefresh(preferred) / xf86ModeVRefresh(i);
+            i->VRefresh = xf86ModeVRefresh(preferred);
+        }
+        for (j = m; j != i; j = j->next) {
+            if (!strcmp(i->name, j->name) &&
+                xf86ModeVRefresh(i) * (1 + SYNC_TOLERANCE) >= xf86ModeVRefresh(j) &&
+                xf86ModeVRefresh(i) * (1 - SYNC_TOLERANCE) <= xf86ModeVRefresh(j)) {
+                i->status = MODE_DUPLICATE;
+            }
+        }
     }
 
     xf86PruneInvalidModes(output->scrn, &m, FALSE);

include/displaymode.h

@@ -47,6 +47,7 @@ typedef enum {
     MODE_ONE_SIZE,              /* only one resolution is supported */
     MODE_NO_REDUCED,            /* monitor doesn't accept reduced blanking */
     MODE_BANDWIDTH,             /* mode requires too much memory bandwidth */
+    MODE_DUPLICATE,             /* mode is duplicated */
     MODE_BAD = -2,              /* unspecified reason */
     MODE_ERROR = -1             /* error condition */
 } ModeStatus;