Index: xserver-xorg-video-intel-2.17.0/src/intel_display.c
===================================================================
--- xserver-xorg-video-intel-2.17.0.orig/src/intel_display.c	2012-01-15 15:38:03.000000000 +0200
+++ xserver-xorg-video-intel-2.17.0/src/intel_display.c	2012-01-15 15:56:32.000000000 +0200
@@ -118,7 +118,8 @@
 #define BACKLIGHT_CLASS "/sys/class/backlight"
 
 /*
- * List of available kernel interfaces in priority order
+ * List of available kernel interfaces in priority order.
+ * May be overridden by a model-specific workaround.
  */
 static const char *backlight_interfaces[] = {
 	"asus-laptop",
@@ -240,28 +241,55 @@
 	return max;
 }
 
+static Bool
+intel_output_backlight_probe(xf86OutputPtr output, const char *iface)
+{
+	struct intel_output *intel_output = output->driver_private;
+	char path[BACKLIGHT_PATH_LEN];
+	struct stat buf;
+
+	sprintf(path, "%s/%s", BACKLIGHT_CLASS, iface);
+	if (!stat(path, &buf)) {
+		intel_output->backlight_iface = iface;
+		intel_output->backlight_max = intel_output_backlight_get_max(output);
+		if (intel_output->backlight_max > 0) {
+			intel_output->backlight_active_level = intel_output_backlight_get(output);
+			xf86DrvMsg(output->scrn->scrnIndex, X_INFO,
+				   "found backlight control interface %s\n", path);
+			return TRUE;
+		}
+	}
+
+	return FALSE;
+}
+
 static void
 intel_output_backlight_init(xf86OutputPtr output)
 {
 	struct intel_output *intel_output = output->driver_private;
+	intel_screen_private *intel = intel_get_screen_private(output->scrn);
 	int i;
 
-	for (i = 0; backlight_interfaces[i] != NULL; i++) {
-		char path[BACKLIGHT_PATH_LEN];
-		struct stat buf;
+	/* Debian bug 651741: With Linux 3.1.0 on Sony VAIO VPCYA1V9E,
+	 * both acpi_video0 and intel_backlight exist and can be
+	 * adjusted, but only intel_backlight affects the display.
+	 */
+	if (VENDOR_ID(intel->PciInfo) == 0x8086 /* Intel */
+	    && DEVICE_ID(intel->PciInfo) == PCI_CHIP_IRONLAKE_M_G
+	    && CHIP_REVISION(intel->PciInfo) == 0x02
+	    && SUBVENDOR_ID(intel->PciInfo) == 0x104d /* Sony */
+	    && SUBSYS_ID(intel->PciInfo) == 0x907c) {
+		xf86DrvMsg(output->scrn->scrnIndex, X_INFO,
+			   "will prefer intel_backlight on this Sony VAIO model\n");
+		if (intel_output_backlight_probe(output, "intel_backlight"))
+			return;
+	}
 
-		sprintf(path, "%s/%s", BACKLIGHT_CLASS, backlight_interfaces[i]);
-		if (!stat(path, &buf)) {
-			intel_output->backlight_iface = backlight_interfaces[i];
-			intel_output->backlight_max = intel_output_backlight_get_max(output);
-			if (intel_output->backlight_max > 0) {
-				intel_output->backlight_active_level = intel_output_backlight_get(output);
-				xf86DrvMsg(output->scrn->scrnIndex, X_INFO,
-					   "found backlight control interface %s\n", path);
-				return;
-			}
-		}
+	for (i = 0; backlight_interfaces[i] != NULL; i++) {
+		if (intel_output_backlight_probe(output, backlight_interfaces[i]))
+			return;
 	}
+
 	intel_output->backlight_iface = NULL;
 }