[RFC 0/2] Add AUX device entries for DP MST devices

[Ville Syrjälä]

On Fri, Apr 12, 2019 at 12:05:29PM -0400, sunpeng.li at amd.com wrote:
> From: Leo Li <sunpeng.li at amd.com>
> 
> Hi all,
> 
> This is a follup to this change made by Ville to add MST aux nodes:
> https://github.com/vsyrjala/linux/commit/cac63f799ee2f5fbbe4f0a375383f13e03d640a5
> Patch 2/2 describes what I added on top.

Cool. I take you got it to actually work? IIRC I never managed that :P

> 
> Sending as an RFC since there are some items I'm not certain on:
> 
> 1) Only expose aux devices for physical ports. FWICT, only DPTX and DPRX
>    can handle AUX transactions, leaving logical ports out.

Hmm. My MST-foo is admittedly weak so I'm not sure. A quick trawl through
the spec didn't provide any solid explanations either :( However eg.
"Figure 2-83: Example Multi-function MST Branch-Sink Device Enumeration"
in the DP 1.4 spec does appear to show kind of virtual DPCD thing behind
a logical port. But I'm not really sure what than means.

> 2) Naming of exposed AUX devices. I'm not sure if the scheme implemented
>    here is the best approach.

I'm not sure magic naming schemes are the best. I believe we do have
the sysfs hierarchy which allows you to find the right aux dev for
the connector, but I do admit that can be a bit cumbersome to use.
Also I'm not sure if all the things we might want to talk to are
even represented by a connector, so maybe we do need something else.

> 
> Let me know your thoughts,
> Leo
> 
> Leo Li (1):
>   drm/dp_mst: Use non-cyclic idr, add suffix option for aux device
> 
> Ville Syrjälä (1):
>   drm/dp_mst: Register aux-dev nodes for MST ports
> 
>  drivers/gpu/drm/drm_crtc_helper_internal.h |   5 +-
>  drivers/gpu/drm/drm_dp_aux_dev.c           |  21 ++++--
>  drivers/gpu/drm/drm_dp_helper.c            |   2 +-
>  drivers/gpu/drm/drm_dp_mst_topology.c      | 109 +++++++++++++++++++++++++----
>  include/drm/drm_dp_helper.h                |   4 ++
>  include/drm/drm_dp_mst_helper.h            |   6 ++
>  6 files changed, 125 insertions(+), 22 deletions(-)
> 
> -- 
> 2.7.4

-- 
Ville Syrjälä
Intel