bcb32b691c
- Move the common vtable stuff to the top - Move "Tile Group" to a more appropriate heading level - Throw away the old intro for the crtc helpers (it's entirely stale, e.g. helpers have become modular years ago), and replace it with a general intro about the motivation behind helpers. - Reorder helpers to group them together a bit better, and explain that grouping in the intro. - Make sure the introductory DOC section is always first. v2: - Remove bogus files accidentally added (Sean). - Spelling fixes (Sean). Cc: Sean Paul <seanpaul@chromium.org> Reviewed-by: Sean Paul <seanpaul@chromium.org> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1471034937-651-2-git-send-email-daniel.vetter@ffwll.ch
114 lines
5 KiB
ReStructuredText
114 lines
5 KiB
ReStructuredText
===================
|
|
Userland interfaces
|
|
===================
|
|
|
|
The DRM core exports several interfaces to applications, generally
|
|
intended to be used through corresponding libdrm wrapper functions. In
|
|
addition, drivers export device-specific interfaces for use by userspace
|
|
drivers & device-aware applications through ioctls and sysfs files.
|
|
|
|
External interfaces include: memory mapping, context management, DMA
|
|
operations, AGP management, vblank control, fence management, memory
|
|
management, and output management.
|
|
|
|
Cover generic ioctls and sysfs layout here. We only need high-level
|
|
info, since man pages should cover the rest.
|
|
|
|
libdrm Device Lookup
|
|
====================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_ioctl.c
|
|
:doc: getunique and setversion story
|
|
|
|
|
|
Primary Nodes, DRM Master and Authentication
|
|
============================================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_auth.c
|
|
:doc: master and authentication
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_auth.c
|
|
:export:
|
|
|
|
.. kernel-doc:: include/drm/drm_auth.h
|
|
:internal:
|
|
|
|
Open-Source Userspace Requirements
|
|
==================================
|
|
|
|
Render nodes
|
|
============
|
|
|
|
DRM core provides multiple character-devices for user-space to use.
|
|
Depending on which device is opened, user-space can perform a different
|
|
set of operations (mainly ioctls). The primary node is always created
|
|
and called card<num>. Additionally, a currently unused control node,
|
|
called controlD<num> is also created. The primary node provides all
|
|
legacy operations and historically was the only interface used by
|
|
userspace. With KMS, the control node was introduced. However, the
|
|
planned KMS control interface has never been written and so the control
|
|
node stays unused to date.
|
|
|
|
With the increased use of offscreen renderers and GPGPU applications,
|
|
clients no longer require running compositors or graphics servers to
|
|
make use of a GPU. But the DRM API required unprivileged clients to
|
|
authenticate to a DRM-Master prior to getting GPU access. To avoid this
|
|
step and to grant clients GPU access without authenticating, render
|
|
nodes were introduced. Render nodes solely serve render clients, that
|
|
is, no modesetting or privileged ioctls can be issued on render nodes.
|
|
Only non-global rendering commands are allowed. If a driver supports
|
|
render nodes, it must advertise it via the DRIVER_RENDER DRM driver
|
|
capability. If not supported, the primary node must be used for render
|
|
clients together with the legacy drmAuth authentication procedure.
|
|
|
|
If a driver advertises render node support, DRM core will create a
|
|
separate render node called renderD<num>. There will be one render node
|
|
per device. No ioctls except PRIME-related ioctls will be allowed on
|
|
this node. Especially GEM_OPEN will be explicitly prohibited. Render
|
|
nodes are designed to avoid the buffer-leaks, which occur if clients
|
|
guess the flink names or mmap offsets on the legacy interface.
|
|
Additionally to this basic interface, drivers must mark their
|
|
driver-dependent render-only ioctls as DRM_RENDER_ALLOW so render
|
|
clients can use them. Driver authors must be careful not to allow any
|
|
privileged ioctls on render nodes.
|
|
|
|
With render nodes, user-space can now control access to the render node
|
|
via basic file-system access-modes. A running graphics server which
|
|
authenticates clients on the privileged primary/legacy node is no longer
|
|
required. Instead, a client can open the render node and is immediately
|
|
granted GPU access. Communication between clients (or servers) is done
|
|
via PRIME. FLINK from render node to legacy node is not supported. New
|
|
clients must not use the insecure FLINK interface.
|
|
|
|
Besides dropping all modeset/global ioctls, render nodes also drop the
|
|
DRM-Master concept. There is no reason to associate render clients with
|
|
a DRM-Master as they are independent of any graphics server. Besides,
|
|
they must work without any running master, anyway. Drivers must be able
|
|
to run without a master object if they support render nodes. If, on the
|
|
other hand, a driver requires shared state between clients which is
|
|
visible to user-space and accessible beyond open-file boundaries, they
|
|
cannot support render nodes.
|
|
|
|
VBlank event handling
|
|
=====================
|
|
|
|
The DRM core exposes two vertical blank related ioctls:
|
|
|
|
DRM_IOCTL_WAIT_VBLANK
|
|
This takes a struct drm_wait_vblank structure as its argument, and
|
|
it is used to block or request a signal when a specified vblank
|
|
event occurs.
|
|
|
|
DRM_IOCTL_MODESET_CTL
|
|
This was only used for user-mode-settind drivers around modesetting
|
|
changes to allow the kernel to update the vblank interrupt after
|
|
mode setting, since on many devices the vertical blank counter is
|
|
reset to 0 at some point during modeset. Modern drivers should not
|
|
call this any more since with kernel mode setting it is a no-op.
|
|
|
|
This second part of the GPU Driver Developer's Guide documents driver
|
|
code, implementation details and also all the driver-specific userspace
|
|
interfaces. Especially since all hardware-acceleration interfaces to
|
|
userspace are driver specific for efficiency and other reasons these
|
|
interfaces can be rather substantial. Hence every driver has its own
|
|
chapter.
|