drm/nv50: fix monitor detection on certain chipsets

There appears to be some kind of switch on certain chips to control whether
the DP auxch or traditional i2c bus will be operational on a connector,
this commit hopefully fixes nouveau to do the right thing.

Likely only relevent on chips with DP outputs.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_i2c.c

@@ -254,16 +254,27 @@ struct nouveau_i2c_chan *
 nouveau_i2c_find(struct drm_device *dev, int index)
 {
 	struct drm_nouveau_private *dev_priv = dev->dev_private;
-	struct nvbios *bios = &dev_priv->vbios;
+	struct dcb_i2c_entry *i2c = &dev_priv->vbios.dcb.i2c[index];
 
 	if (index >= DCB_MAX_NUM_I2C_ENTRIES)
 		return NULL;
 
-	if (!bios->dcb.i2c[index].chan) {
-		if (nouveau_i2c_init(dev, &bios->dcb.i2c[index], index))
-			return NULL;
+	if (dev_priv->chipset >= NV_50 && (i2c->entry & 0x00000100)) {
+		uint32_t reg = 0xe500, val;
+
+		if (i2c->port_type == 6) {
+			reg += i2c->read * 0x50;
+			val  = 0x2002;
+		} else {
+			reg += ((i2c->entry & 0x1e00) >> 9) * 0x50;
+			val  = 0xe001;
+		}
+
+		nv_wr32(dev, reg, (nv_rd32(dev, reg) & ~0xf003) | val);
 	}
 
-	return bios->dcb.i2c[index].chan;
+	if (!i2c->chan && nouveau_i2c_init(dev, i2c, index))
+		return NULL;
+	return i2c->chan;
 }