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SubjectRe: Thunderbolt DP oddity on v5.2.9 on iMac 12,2
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)
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