diff options
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/drm.tmpl | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl index 9fc8ed4ac0f4..ed1d6d289022 100644 --- a/Documentation/DocBook/drm.tmpl +++ b/Documentation/DocBook/drm.tmpl @@ -205,6 +205,12 @@ Driver implements DRM PRIME buffer sharing. </para></listitem> </varlistentry> + <varlistentry> + <term>DRIVER_RENDER</term> + <listitem><para> + Driver supports dedicated render nodes. + </para></listitem> + </varlistentry> </variablelist> </sect3> <sect3> @@ -2644,6 +2650,69 @@ int (*resume) (struct drm_device *);</synopsis> info, since man pages should cover the rest. </para> + <!-- External: render nodes --> + + <sect1> + <title>Render nodes</title> + <para> + 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 <term>card<num></term>. Additionally, a currently + unused control node, called <term>controlD<num></term> 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. + </para> + <para> + 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 <term>DRIVER_RENDER</term> + DRM driver capability. If not supported, the primary node must be used + for render clients together with the legacy drmAuth authentication + procedure. + </para> + <para> + If a driver advertises render node support, DRM core will create a + separate render node called <term>renderD<num></term>. There will + be one render node per device. No ioctls except PRIME-related ioctls + will be allowed on this node. Especially <term>GEM_OPEN</term> 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 + <term>DRM_RENDER_ALLOW</term> so render clients can use them. Driver + authors must be careful not to allow any privileged ioctls on render + nodes. + </para> + <para> + 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. + </para> + <para> + 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. + </para> + </sect1> + <!-- External: vblank handling --> <sect1> |