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Date:   Tue, 3 Sep 2019 13:13:25 +0300
From:   Mika Westerberg <mika.westerberg@linux.intel.com>
To:     Brad Campbell <lists2009@fnarfbargle.com>
Cc:     linux-kernel@vger.kernel.org, michael.jamet@intel.com,
        YehezkelShB@gmail.com
Subject: Re: Thunderbolt DP oddity on v5.2.9 on iMac 12,2
Message-ID: <20190903101325.GC2691@lahna.fi.intel.com>
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Hi Brad,

On Thu, Aug 29, 2019 at 12:27:08AM +0800, Brad Campbell wrote:
> It wouldn't surprise me if the firmware was doing something funky. It was
> one of the first Thunderbolt equipped models and the support docs explicitly
> say only one Thunderbolt display in Windows and two in later versions of
> OSX. It almost needs a quirk to say "firmware does something we don't like,
> reset the controller and re-discover from scratch".
> 
> Anyway, I'm not in any hurry. It doesn't get rebooted often and it's not in
> any way preventing me using the machine. In fact, upgrading the third head
> from an old 24" 1920x1200 to the second Thunderbolt display has been
> invaluable.

Can you apply the below patch and then boot with two monitors connected?
Then send me the dmesg. It does not fix anything but should log a bit
more.

diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
index 1f7a9e1cc09c..28a72336558a 100644
--- a/drivers/thunderbolt/tb.c
+++ b/drivers/thunderbolt/tb.c
@@ -313,8 +313,10 @@ static struct tb_port *tb_find_unused_port(struct tb_switch *sw,
 			continue;
 		if (!sw->ports[i].cap_adap)
 			continue;
-		if (tb_port_is_enabled(&sw->ports[i]))
+		if (tb_port_is_enabled(&sw->ports[i])) {
+			tb_port_dbg(&sw->ports[i], "this already enabled\n");
 			continue;
+		}
 		return &sw->ports[i];
 	}
 	return NULL;
@@ -365,16 +367,25 @@ static int tb_tunnel_dp(struct tb *tb, struct tb_port *out)
 	struct tb_tunnel *tunnel;
 	struct tb_port *in;
 
-	if (tb_port_is_enabled(out))
+	tb_port_dbg(out, "trying to tunnel DP\n");
+
+	if (tb_port_is_enabled(out)) {
+		tb_port_dbg(out, "DP OUT port already enabled\n");
 		return 0;
+	}
+
+	tb_port_dbg(out, "finding free DP IN port\n");
 
 	do {
 		sw = tb_to_switch(sw->dev.parent);
 		if (!sw)
 			return 0;
+		tb_sw_dbg(sw, "finding available DP IN\n");
 		in = tb_find_unused_port(sw, TB_TYPE_DP_HDMI_IN);
 	} while (!in);
 
+	tb_port_dbg(in, "found DP IN\n");
+
 	tunnel = tb_tunnel_alloc_dp(tb, in, out);
 	if (!tunnel) {
 		tb_port_dbg(out, "DP tunnel allocation failed\n");
diff --git a/drivers/thunderbolt/tunnel.c b/drivers/thunderbolt/tunnel.c
index 5a99234826e7..93c2c965bdde 100644
--- a/drivers/thunderbolt/tunnel.c
+++ b/drivers/thunderbolt/tunnel.c
@@ -351,9 +351,23 @@ struct tb_tunnel *tb_tunnel_discover_dp(struct tb *tb, struct tb_port *in)
 	struct tb_tunnel *tunnel;
 	struct tb_port *port;
 	struct tb_path *path;
+	u32 data[2];
+	int ret;
+
+	tb_port_dbg(in, "start DP discover\n");
 
-	if (!tb_dp_port_is_enabled(in))
+	if (!tb_dp_port_is_enabled(in)) {
+		tb_port_dbg(in, "DP port enabled\n");
 		return NULL;
+	}
+
+	ret = tb_port_read(in, data, TB_CFG_PORT, in->cap_adap,
+			   ARRAY_SIZE(data));
+	if (ret)
+		return NULL;
+
+	tb_port_dbg(in, "data[0]=0x%08x\n", data[0]);
+	tb_port_dbg(in, "data[1]=0x%08x\n", data[1]);
 
 	tunnel = tb_tunnel_alloc(tb, 3, TB_TUNNEL_DP);
 	if (!tunnel)