Require for drm control-node

[Jared Hu]

Hi All,

I'm a gstreamer developer and is trying to implement a video display plugin based on DRM/KMS which is named "kmssink".

I met a problem that the kmssink will have permission issue when running with x11 and wayland. Because these two window system will hold DRM-Master in their life time. So I'm change the code to use control node "controlD64" for display and file node card0 for memory management. It work really well. Video can show on multi display with wayland and x11. But I notice that in the Linux kernel mainline, below commit remove the control node:

commit 8a357d10043c75e980e7fcdb60d2b913491564af
Author: Daniel Vetter <daniel.vetter at ffwll.ch<mailto:daniel.vetter at ffwll.ch>>
Date:   Fri Oct 28 10:10:50 2016 +0200

    drm: Nerf DRM_CONTROL nodes

    Looking at the ioctl permission checks I noticed that it's impossible
    to import gem buffers into a control nodes, and fd2handle/handle2fd
    also don't work, so no joy with dma-bufs.

    The only way to do anything with a control node is by drawing stuff
    into a dumb buffer and displaying that. I suspect control nodes are an
    entirely unused thing, and a cursory check shows that there does not
    seem to be any callers of drmOpenControl nor of the other drmOpen
    functions using DRM_MODE_CONTROL.

    Since I don't like dead uabi, let's remove it. But since this would be
    a really big change I think it's better to start out small by simply
    not registering anything. We can garbage-collect the dead code later
    on, once we're sure it's really not used anywhere.

    Acked-by: Dave Airlie <airlied at gmail.com<mailto:airlied at gmail.com>>
    Signed-off-by: Daniel Vetter <daniel.vetter at intel.com<mailto:daniel.vetter at intel.com>>
    Link: http://patchwork.freedesktop.org/patch/msgid/20161028081050.1042-1-daniel.vetter@ffwll.ch

This will have big impace on my case, and I cannot figure out how to fix this issue. I think control node is useful, actually many users are using this node for application development including rockchip and amlogic. details please refer to: http://gstreamer-devel.966125.n4.nabble.com/Can-kmssink-run-with-x11-or-wayland-which-is-based-on-drm-kms-also-td4683783.html#a4683819

I'm sending this mail for require restoring control node in file system, or is there any other way to fix my permission issue?

Thanks.

Best wishes

Haihua Hu
MPU Mulitmedia Software
NXP Semiconductors
No.288 ZhuYuan Road
Suzhou New District 215011, P.R.C
Phone: +86-512-680566738
jared.hu at nxp.com
[cid:image003.png at 01D13808.32F8E040]


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