Re: [Intel-gfx] [PATCH 3/3] drm/i915: Support DDI lane reversal for DP

[Benjamin Tissoires]

On Jul 30 2015 or thereabouts, Sivakumar Thulasimani wrote:
> 
> 
> On 7/29/2015 8:52 PM, Benjamin Tissoires wrote:
> >On Jul 29 2015 or thereabouts, Sivakumar Thulasimani wrote:
> >>why not detect reverse in intel_dp_detect/intel_hpd_pulse ? that way you can
> >>identify both lane count and reversal state without touching anything in the
> >>link training code. i am yet to upstream my changes for CHT that i can share
> >>if required that does the same in intel_dp_detect without touching any line
> >>in link training path.
> >With my current limited knowledge of the dp hotplug (and i915 driver) I
> >am not sure we could detect the reversed state without trying to train 1
> >lane only. I'd be glad to look at your changes and test them on my
> >system if you think that could help having a cleaner solution.
> >
> >Cheers,
> >Benjamin
> No, what i recommended was to do link training but in intel_dp_detect. Since
> USB Type C cable
> also has its own lane count restriction (it can have different lane count
> than the one supported
> by panel) you might have to figure that out as well. so both reversal and
> lane count detection
> can be done outside the modeset path and keep the code free of type C
> changes outside
> detection path.
> 
> Please find below the code to do the same. Do not waste time trying to apply
> this directly on
> nightly since this is based on a local tree and because this is pre- atomic
> changes code, so you
> might have to modify chv_upfront_link_train to work on top of the latest
> nightly code. we
> are supposed to upstream this and is in my todo list.
> 

[original patch snipped...]

Hi Sivakumar,

So I managed to manually re-apply your patch on top of
drm-intel-nightly, and tried to port it to make Broadwell working too.
It works OK if the system is already boot without any external DP used.
In this case, the detection works and I can see my external monitor
working properly.

However, if the monitor is cold plugged, the cpu/GPU hangs and I can not
understand why. I think I enabled all that is mentioned in the PRM to be
able to train the DP link, but I am obviously missing something else.
Can you have a look?

My patch is now: