When userspace removes the active framebuffer using DRM_IOCTL_MODE_RMFB,
or explicitly disables the CRTC (by calling drmModeSetCrtc(..., NULL)
for example), a NULL framebuffer will be passed to the .set_config()
implementation of a CRTC. The drm_crtc_helper_set_config() helper will
decide to disable a CRTC when that happens.
To do so, it calls drm_crtc_helper_disable(), which in turn will iterate
over all encoders and decouple them from their connectors and finally
call drm_helper_disable_unused_functions() to clean up and call the
.disable() or .dpms() implementation for each encoder. However, at no
point during this sequence does it track the DPMS mode of a connector,
so it will usually remain on after this.
When a connector is enabled again, drm_helper_connector_dpms() will not
notice that the DPMS mode actually changed and won't do anything, which
causes the connector to stay disabled indefinitely.
To prevent this from happening, explicitly set the connector's DPMS mode
to off when the CRTC is disabled. That way it reflects the correct state
and can be enabled again.
This solves an issue observed when terminating an X server running on
the xf86-video-modesetting driver. Without this patch, the connector
would not be enabled properly and the screen would stay dark.
Acked-by: David Airlie <airlied@linux.ie>
Signed-off-by: Thierry Reding <treding@nvidia.com>
************************************************************
* For the very latest on DRI development, please see: *
* http://dri.freedesktop.org/ *
************************************************************
The Direct Rendering Manager (drm) is a device-independent kernel-level
device driver that provides support for the XFree86 Direct Rendering
Infrastructure (DRI).
The DRM supports the Direct Rendering Infrastructure (DRI) in four major
ways:
1. The DRM provides synchronized access to the graphics hardware via
the use of an optimized two-tiered lock.
2. The DRM enforces the DRI security policy for access to the graphics
hardware by only allowing authenticated X11 clients access to
restricted regions of memory.
3. The DRM provides a generic DMA engine, complete with multiple
queues and the ability to detect the need for an OpenGL context
switch.
4. The DRM is extensible via the use of small device-specific modules
that rely extensively on the API exported by the DRM module.
Documentation on the DRI is available from:
http://dri.freedesktop.org/wiki/Documentation
http://sourceforge.net/project/showfiles.php?group_id=387
http://dri.sourceforge.net/doc/
For specific information about kernel-level support, see:
The Direct Rendering Manager, Kernel Support for the Direct Rendering
Infrastructure
http://dri.sourceforge.net/doc/drm_low_level.html
Hardware Locking for the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/hardware_locking_low_level.html
A Security Analysis of the Direct Rendering Infrastructure
http://dri.sourceforge.net/doc/security_low_level.html
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