Bug 84717 - DP MST: wrong device names in /sys/class/drm
Summary: DP MST: wrong device names in /sys/class/drm
Status: NEW
Alias: None
Product: DRI
Classification: Unclassified
Component: DRM/other (show other bugs)
Version: XOrg git
Hardware: x86-64 (AMD64) Linux (All)
: low enhancement
Assignee: Dave Airlie
QA Contact:
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Reported: 2014-10-06 14:12 UTC by Daniel Michalik
Modified: 2015-10-23 10:12 UTC (History)
2 users (show)

See Also:
i915 platform:
i915 features: display/DP MST


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Description Daniel Michalik 2014-10-06 14:12:49 UTC
With latest version of the intel driver (ec2b9ac81aed0d2dda2948171ca1c260184bf221) I find the MST devices correctly named (DP2-subid) in xrandr:
# xrandr|grep connected
eDP1 connected 1920x1080+0+1080 (normal left inverted right x axis y axis) 309mm x 175mm
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP2-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 531mm x 299mm
DP2-2 connected 1200x1600+1920+0 left (normal left inverted right x axis y axis) 432mm x 324mm
DP2-3 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

However in /sys/class/drm the folders follow the old naming scheme:
# ls /sys/class/drm/
card0  card0-DP-1  card0-DP-2  card0-DP-3  card0-DP-4  card0-DP-5  card0-eDP-1  card0-HDMI-A-1  card0-HDMI-A-2  controlD64  renderD128  version

I am not sure as of yet whether the mapping between the continuous numbers and the MST devices is persistent. I would have expected to find the same naming used in /sys/class/drm as I found in xrandr. Please let me know what additional information to supply.
Comment 1 Chris Wilson 2014-10-07 09:37:53 UTC
I am not too sure we want the dynamic renaming of connectors here - but maybe a set of symlinks from topological name to "canonical" name?
Comment 2 Daniel Michalik 2014-10-08 12:14:20 UTC
Symlinks sound like a good idea to me. Background: Udev triggers xrandr to autoconfigure. Currently I use /sys/class/drm/*/status to determine which devices are connected. Coming to think, I could of course also grep xrandr -q ... yet I think additional symlinks would make it nicer to understand. I see you changed the bug report to 'enhancement', I think this is reasonable.
Comment 3 Jani Nikula 2015-01-29 13:24:31 UTC
CC Dave.


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