--- xc/programs/Xserver/hw/xfree86/drivers/ati/radeon_reg.h.pci_detect_orig	2003-09-30 12:40:35.000000000 -0400
+++ xc/programs/Xserver/hw/xfree86/drivers/ati/radeon_reg.h	2003-09-30 12:41:37.000000000 -0400
@@ -66,6 +66,8 @@
 #       define RADEON_AGP_APER_SIZE_4MB     (0x3f << 0)
 #       define RADEON_AGP_APER_SIZE_MASK    (0x3f << 0)
 #define RADEON_AGP_COMMAND                  0x0f60 /* PCI */
+#define RADEON_AGP_COMMAND_PCI_CONFIG       0x0060 /* offset in PCI config*/
+#       define RADEON_AGP_ENABLE            (1<<8)
 #define RADEON_AGP_PLL_CNTL                 0x000b /* PLL */
 #define RADEON_AGP_STATUS                   0x0f5c /* PCI */
 #       define RADEON_AGP_1X_MODE           0x01

--- xc/programs/Xserver/hw/xfree86/drivers/ati/radeon_driver.c.pci_detect_orig	2003-09-30 12:40:35.000000000 -0400
+++ xc/programs/Xserver/hw/xfree86/drivers/ati/radeon_driver.c	2003-09-30 12:41:37.000000000 -0400
@@ -110,7 +110,7 @@
     OPTION_DAC_6BIT,
     OPTION_DAC_8BIT,
 #ifdef XF86DRI
-    OPTION_IS_PCI,
+    OPTION_BUS_TYPE,
     OPTION_CP_PIO,
     OPTION_USEC_TIMEOUT,
     OPTION_AGP_MODE,
@@ -140,7 +140,7 @@
     { OPTION_DAC_6BIT,       "Dac6Bit",          OPTV_BOOLEAN, {0}, FALSE },
     { OPTION_DAC_8BIT,       "Dac8Bit",          OPTV_BOOLEAN, {0}, TRUE  },
 #ifdef XF86DRI
-    { OPTION_IS_PCI,         "ForcePCIMode",     OPTV_BOOLEAN, {0}, FALSE },
+    { OPTION_BUS_TYPE,       "BusType",          OPTV_ANYSTR,  {0}, FALSE },
     { OPTION_CP_PIO,         "CPPIOMode",        OPTV_BOOLEAN, {0}, FALSE },
     { OPTION_USEC_TIMEOUT,   "CPusecTimeout",    OPTV_INTEGER, {0}, FALSE },
     { OPTION_AGP_MODE,       "AGPMode",          OPTV_INTEGER, {0}, FALSE },
@@ -1871,6 +1871,7 @@
     int            offset = 0; /* RAM Type */
     MessageType    from;
     unsigned char *RADEONMMIO = info->MMIO;
+    const char *s;
 
 				/* Chipset */
     from = X_PROBED;
@@ -2141,12 +2142,40 @@
 
 #ifdef XF86DRI
 				/* AGP/PCI */
-    if (xf86ReturnOptValBool(info->Options, OPTION_IS_PCI, FALSE)) {
-	info->IsPCI = TRUE;
-	xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "Forced into PCI-only mode\n");
-    } else {
-	/* TODO: we'll need a reliable way to detect PCI bus here. */
-	info->IsPCI = FALSE; 
+    if ((s = xf86GetOptValString(info->Options, OPTION_BUS_TYPE))) {
+	if (strcmp(s, "AGP") == 0) {
+	    info->IsPCI = FALSE;
+	    xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "Forced into AGP mode\n");
+	} else if (strcmp(s, "PCI") == 0) {
+	    info->IsPCI = TRUE;
+	    xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "Forced into PCI mode\n");
+	} else if (strcmp(s, "PCIE") == 0) {
+	    info->IsPCI = TRUE;
+	    xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "PCI Express not supported yet, use PCI mode\n");
+	} else {
+	    info->IsPCI = FALSE;
+	    s = NULL;
+	    xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "Invalid BusType option, use detected type\n");
+	}
+    } 
+
+    if (!s) {
+	CARD32 tmp = pciReadLong(info->PciTag, RADEON_AGP_COMMAND_PCI_CONFIG);
+	/* There are signatures in BIOS and PCI-SSID for a PCI card, but they are not very reliable.
+	   Following detection method works for all cards tested so far.
+	   Note, checking AGP_ENABLE bit after drmAgpEnable call can also give the correct result.
+	   However, calling drmAgpEnable on a PCI card can cause some strange lockup when the server
+	   restarts next time.
+	*/
+	pciWriteLong(info->PciTag, RADEON_AGP_COMMAND_PCI_CONFIG, tmp | RADEON_AGP_ENABLE);
+	if (pciReadLong(info->PciTag, RADEON_AGP_COMMAND_PCI_CONFIG) & RADEON_AGP_ENABLE) {
+	    info->IsPCI = FALSE; 
+	    xf86DrvMsg(pScrn->scrnIndex, X_INFO, "AGP card detected\n");
+	} else {
+	    info->IsPCI = TRUE; 
+	    xf86DrvMsg(pScrn->scrnIndex, X_INFO, "PCI card detected\n");
+	}
+	pciWriteLong(info->PciTag, RADEON_AGP_COMMAND_PCI_CONFIG, tmp);
     }
 #endif
 
--- xc/programs/Xserver/hw/xfree86/drivers/ati/radeon.man.pci_detect_orig	2003-09-30 12:40:57.000000000 -0400
+++ xc/programs/Xserver/hw/xfree86/drivers/ati/radeon.man	2003-09-30 12:41:37.000000000 -0400
@@ -143,13 +143,22 @@
 The default is
 .B off.
 .TP 
-.BI "Option \*qForcePCIMode\*q \*q" boolean \*q
-Force to use PCI GART for DRI acceleration.
+.BI "Option \*qBusType\*q \*q" string \*q
+Used to replace previous ForcePCIMode option.
+Should only be used when driver's bus detection is incorrect
+or you want to force a AGP card to PCI mode. Should NEVER force
+a PCI card to AGP bus.
+.br
+PCI    \-\- PCI bus
+.br
+AGP    \-\- AGP bus
+.br
+PCIE   \-\- PCI Express (falls back to PCI at present)
 .br
 (used only when DRI is enabled)
 .br
 The default is
-.B off.
+.B auto detect.
 .TP 
 .BI "Option \*qDDCMode\*q \*q" boolean \*q
 Force to use the modes queried from the connected monitor.