To get an image from KWin to the screen in the DRM pipeline we combine a CRTC,
an encoder and a connector. These objects are static in the sense, that they
represent real hardware on the graphics card, which doesn't change in a
session. See here for more details:
https://01.org/linuxgraphics/gfx-docs/drm/gpu/drm-kms.html
Until now we used DrmOutput as the main representation for such an active
rendering pipeline. I.e. it gets created and destroyed on hot plug events of
displays. On the other side we had no fixed representation of the static kernel
objects throughout the lifetime of KWin. This has several disadvantages:
* We always need to query all available static objects on an hot plug event.
* We can't manipulate the frame buffer of a CRTC after an output has been
disconnected
* Adding functionality for driving multiple displays on a single CRTC (i.e.
cloning) would be difficult
* We can't destroy the last frame buffer on display disconnect because the CRTC
still accesses it and have therefore a memory leak on every display disconnect
This patch solves these issues by storing representations of all available CRTC
and Connector objects in DrmBackend on init via DrmCrtc and DrmConnector
instances. On an hotplug event these vectors are looped for a fitting CRTC and
Connector combinations. Buffer handling is moved to the respective CRTC
instance. All changes in overview:
* Query all available CRTCs and Connectors and save for subsequent hotplug
events
* Fix logic errors in `queryResources()`
* Move framebuffers, buffer flip and blank logic in DrmCrtc
* Remove `restoreSaved()`. It isn't necessary and is dangerous if the old
framebuffer was deleted in the meantime. Also could reveal sensitive user
info from old session.
Test Plan:
Login, logout, VT switching, connect and disconnect external monitor, energy
saving mode.
Reviewers: #kwin
Subscribers: kwin, #kwin
Tags: #kwin
Differential Revision: https://phabricator.kde.org/D5118
This is Milestone 1 of full support of Atomic Mode Setting (AMS) and
Universal Planes in the KWin DRM backend.
With Milestone 1 we can use the primary plane of a DRM output and do an
AMS commit (this means mode setting aswell as page flipping), if the
driver supports it. Until now the functionality is only tested on Intel
graphics. You need the drm-next kernel for most recent DRM kernel
developments. As boot option set "i915.nuclear_pageflip". Additionally
at the moment AMS is still hidden behind the environment variable
KWIN_DRM_AMS. Set it, if you want to try out AMS.
What needs to be done next: Make it possible to transfer EGL buffers
directly to planes and implement logic for deciding about using a plane
or not for a specific buffer.
You can read more about it on LWN:
https://lwn.net/Articles/653071
And on Martin's blog:
https://blog.martin-graesslin.com/blog/2015/08/layered-compositing/
I used as model previous work by Daniel Stone for Weston:
https://git.collabora.com/cgit/user/daniels/weston.git
Reviewed-by: mgraesslin
Tags: #kwin
Differential Revision: https://phabricator.kde.org/D2370
