Bug 84717

Summary:	DP MST: wrong device names in /sys/class/drm
Product:	DRI	Reporter:	Daniel Michalik <dev>
Component:	DRM/other	Assignee:	Dave Airlie <airlied>
Status:	RESOLVED INVALID	QA Contact:
Severity:	enhancement
Priority:	low	CC:	airlied, dri-devel
Version:	XOrg git
Hardware:	x86-64 (AMD64)
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:	display/DP MST

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.

Comment 4 Martin Peres 2019-10-14 13:20:19 UTC

Hi,

Freedesktop's Bugzilla instance is EOLed and open bugs are about to be migrated to http://gitlab.freedesktop.org.

To avoid migrating out of date bugs, I am now closing all the bugs that did not see any activity in the past year. If the issue is still happening, please create a new bug in the relevant project at https://gitlab.freedesktop.org/drm (use misc by default).

Sorry about the noise!

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