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Date:   Tue, 3 Sep 2019 13:36:03 +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: <20190903103603.GD2691@lahna.fi.intel.com>
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On Tue, Sep 03, 2019 at 01:13:28PM +0300, Mika Westerberg wrote:
> 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");

I did typo here so while you try apply the patch, please change this one
to say "DP port not enabled" instead.