Re: [PATCH 0/3] Propagate DP-over-Type-C hotplug events from Type-C subsys to drm-drivers

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

On Wed, Feb 27, 2019 at 01:16:27PM +0200, Jani Nikula wrote:
> On Wed, 27 Feb 2019, Heikki Krogerus <heikki.krogerus@linux.intel.com> wrote:
> > One thing that this series does not consider is the DP lane count
> > problem. The GPU drivers (i915 in this case) does not know is four,
> > two or one DP lanes in use.
> 
> Also, orientation.
> 
> > I guess that is not a critical issue since there is a workaround (I
> > think) where the driver basically does trial and error, but ideally we
> > should be able to tell i915 also the pin assignment that was
> > negotiated with the partner device so it knows the DP lane count.
> 
> Yeah, if the information is there, we'd like to know. With the
> orientation, there's a worst case of sixth attempt of finding out
> there's just one lane in a certain orientation. Couple that with link
> rate selection (did it not work because too high link rate or because
> the lanes are just not there?) we get pretty confused about what we
> should try.

The orientation is also considered in the alt mode API. We have a
function for that typec_altmode_get_orientation(), but it of course
requires that the caller has a handle to the alt mode object. So
basically we would again need tight coupling between the DP connector
and USB Type-C connector.

Hans, I'm not so sure we should, or can, rule out the "tight coupling"
option after all.


thanks,

-- 
heikki
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