drm/nouveau: Disable AGP on PowerPC again.

Signed-off-by: Francisco Jerez <[e-mail]>
Signed-off-by: Ben Skeggs <[e-mail]>

drivers/gpu/drm/nouveau/nouveau_agp.c

···
 	if (drm->agp.stat == UNKNOWN) {
 		if (!nouveau_agpmode)
 			return false;
+#ifdef __powerpc__
+		/* Disable AGP by default on all PowerPC machines for
+		 * now -- At least some UniNorth-2 AGP bridges are
+		 * known to be broken: DMA from the host to the card
+		 * works just fine, but writeback from the card to the
+		 * host goes straight to memory untranslated bypassing
+		 * the GATT somehow, making them quite painful to deal
+		 * with...
+		 */
+		if (nouveau_agpmode == -1)
+			return false;
+#endif
 		return true;
 	}