how can I identify which video card on a mutli-card linux box a display belongs to

Zhang Fan zhangfan at
Mon Nov 10 00:31:59 PST 2014

Hi all,
I'm developing a video matrix system for Linux.  Typically multiple 
vendors' video card and/or multiple cards of same vendor/model might be 
used in one system.
I can list the display by using 'xrandr' program and read the display 
card information from /sys/class/drm/ directory. But I can't figure out 
how to relate these two kinds information. i.e, which card/port does a 
display belongs to?
'xrandr --verbose' command lists the 'Identifier' of each display but it 
seems volatile and might change after reboot and has nothing to do with 
the information in /sys/class/drm.

Zhang Fan
Ubique Solutions Ltd.
Tel: (+86)20 37588645(603)
Fax: (+86)20 37588645(612)
Email: zhangfan at
Room 19D, 19/F, Chunk kiu Building
76 Xian Lei Zhong Road Guangzhou(510070)

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