drm/nv50: fix a couple of vm init issues

Fixes overwriting the first page table entry when testing that the PRAMIN
BAR can be correctly read/written, and adds an additional bar flush after
poking the BAR3 control regs.
Signed-off-by: NFrancisco Jerez <currojerez@riseup.net>
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nv50_instmem.c

@@ -182,16 +182,17 @@ nv50_instmem_init(struct drm_device *dev)
 	nv_wr32(dev, 0x001704, 0x40000000 | (chan->ramin->vinst >> 12));
 	nv_wr32(dev, 0x00170c, 0x80000000 | (priv->bar3_dmaobj->cinst >> 4));
 
-	tmp = nv_ri32(dev, 0);
-	nv_wi32(dev, 0, ~tmp);
-	if (nv_ri32(dev, 0) != ~tmp) {
+	dev_priv->engine.instmem.flush(dev);
+	dev_priv->ramin_available = true;
+
+	tmp = nv_ro32(chan->ramin, 0);
+	nv_wo32(chan->ramin, 0, ~tmp);
+	if (nv_ro32(chan->ramin, 0) != ~tmp) {
 		NV_ERROR(dev, "PRAMIN readback failed\n");
 		ret = -EIO;
 		goto error;
 	}
-	nv_wi32(dev, 0, tmp);
-
-	dev_priv->ramin_available = true;
+	nv_wo32(chan->ramin, 0, tmp);
 
 	/* BAR1 */
 	ret = nouveau_vm_new(dev, BAR1_VM_BASE, BAR1_VM_SIZE, BAR1_VM_BASE,