--- XFree86-4.2.1/xc/programs/Xserver/hw/xfree86/drivers/tdfx/tdfxdefs.h.orig	Thu Apr  5 23:29:17 2001
+++ XFree86-4.2.1/xc/programs/Xserver/hw/xfree86/drivers/tdfx/tdfxdefs.h	Thu Sep  5 21:46:01 2002
@@ -45,6 +45,7 @@
 #define SST_DESKTOP_EN                  BIT(7)
 #define SST_DESKTOP_PIXEL_FORMAT_SHIFT  18
 #define SST_DESKTOP_CLUT_BYPASS         BIT(10)
+#define SST_INTERLACE                   BIT(3)
 #define SST_HALF_MODE                   BIT(4)
 #define SST_CURSOR_EN                   BIT(27)
 #define SST_FBI_BUSY                    BIT(7)
--- XFree86-4.2.1/xc/programs/Xserver/hw/xfree86/drivers/tdfx/tdfx_driver.c.orig	Wed Sep 18 03:02:14 2002
+++ XFree86-4.2.1/xc/programs/Xserver/hw/xfree86/drivers/tdfx/tdfx_driver.c	Wed Sep 18 13:41:20 2002
@@ -960,7 +960,18 @@
   clockRanges->minClock= 12000; /* !!! What's the min clock? !!! */
   clockRanges->maxClock=pTDFX->MaxClock;
   clockRanges->clockIndex = -1;
-  clockRanges->interlaceAllowed = FALSE;
+  switch (pTDFX->ChipType) {
+    case PCI_CHIP_BANSHEE:
+      clockRanges->interlaceAllowed = FALSE;
+      break;
+    case PCI_CHIP_VOODOO3:
+    case PCI_CHIP_VOODOO5:
+      clockRanges->interlaceAllowed = TRUE;
+      break;
+    default:
+      clockRanges->interlaceAllowed = FALSE;
+      break;
+  }    
   clockRanges->doubleScanAllowed = TRUE;
 
   /*
@@ -990,7 +1001,7 @@
     return FALSE;
   }
 
-  xf86SetCrtcForModes(pScrn, INTERLACE_HALVE_V);
+  xf86SetCrtcForModes(pScrn, 0);
 
   pScrn->currentMode = pScrn->modes;
 
@@ -1666,6 +1677,10 @@
     tdfxReg->screensize=mode->HDisplay|(mode->VDisplay<<12);
     tdfxReg->vidcfg &= ~SST_HALF_MODE;
   }
+  if (mode->Flags&V_INTERLACE) {
+    tdfxReg->vidcfg|=SST_INTERLACE;
+  } else
+    tdfxReg->vidcfg&=~SST_INTERLACE;
 
   TDFXTRACEREG("cpp=%d Hdisplay=%d Vdisplay=%d stride=%d screensize=%x\n", 
 	     pTDFX->cpp, mode->HDisplay, mode->VDisplay, tdfxReg->stride, 
@@ -2394,12 +2409,29 @@
 
 static int
 TDFXValidMode(int scrnIndex, DisplayModePtr mode, Bool verbose, int flags) {
+  ScrnInfoPtr pScrn;
+  TDFXPtr pTDFX;
+
   TDFXTRACE("TDFXValidMode start\n");
   if ((mode->HDisplay>2048) || (mode->VDisplay>1536)) 
     return MODE_BAD;
-  /* Banshee doesn't support interlace. Does V3? */
-  if (mode->Flags&V_INTERLACE) 
-    return MODE_BAD;
+  /* Banshee doesn't support interlace, but Voodoo 3 and higher do. */
+  pScrn = xf86Screens[scrnIndex];
+  pTDFX = TDFXPTR(pScrn);
+  if (mode->Flags&V_INTERLACE) {
+    switch (pTDFX->ChipType) {
+      case PCI_CHIP_BANSHEE:
+        return MODE_BAD;
+        break;
+      case PCI_CHIP_VOODOO3:
+      case PCI_CHIP_VOODOO5:
+        return MODE_OK;
+        break;
+      default:
+        return MODE_BAD;
+        break;
+    }
+  }
   /* In clock doubled mode widths must be divisible by 16 instead of 8 */
   if ((mode->Clock>TDFX2XCUTOFF) && (mode->HDisplay%16))
     return MODE_BAD;