linux-kernel - Re: Thunderbolt DP oddity on v5.2.9 on iMac 12,2

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Message-ID: <30fe86c0-e4f9-e852-a4d8-7b8263b373ef@fnarfbargle.com>
Date:   Tue, 3 Sep 2019 20:54:02 +0800
From:   Brad Campbell <lists2009@...rfbargle.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, michael.jamet@...el.com,
        YehezkelShB@...il.com
Subject: Re: Thunderbolt DP oddity on v5.2.9 on iMac 12,2

On 3/9/19 7:55 pm, Mika Westerberg wrote:
> On Tue, Sep 03, 2019 at 07:11:32PM +0800, Brad Campbell wrote:
> 
> I think the problem is that for some reason, probably because this is
> first generation hardware with all the bugs included, you cannot read
> the second dword from DP adapter path config space (you can write it
> though).
> 
> I've updated the patch so that it reads only the first dword when it
> discovers paths and also when it disables them. Can you try it out and
> see if it makes a difference? This should also get rid of the warnings
> you get.
> 

It would seem so. Now I get 3 heads on a cold or warm boot and no 
warnings in the log, so it looks like that did the job. I've attached 
the dmesg from the last cold boot for reference.

I forgot to mention I did try the chained monitors over the weekend, but 
that resulted in some carnage (corrupted displays and some form of hard 
lock when starting X). I've not had a chance to get netconsole 
configured up to catch any wreckage when it explodes as it didn't leave 
anything on disk.

I will do that in the next couple of days just for completeness.

I really appreciate you looking into this given it's probably one of 
those .001% corner cases.

Regards,
Brad

View attachment "dmesg.09" of type "text/plain" (131668 bytes)