Signed-off-by: Tomohito Esaki etom@igel.co.jp --- Documentation/gpu/drivers.rst | 1 + Documentation/gpu/vdrm.rst | 51 +++++++++++++++++++++++++++++++++++ 2 files changed, 52 insertions(+) create mode 100644 Documentation/gpu/vdrm.rst
diff --git a/Documentation/gpu/drivers.rst b/Documentation/gpu/drivers.rst index b4a0ed3ca961..bad0226de972 100644 --- a/Documentation/gpu/drivers.rst +++ b/Documentation/gpu/drivers.rst @@ -19,6 +19,7 @@ GPU Driver Documentation xen-front afbc komeda-kms + vdrm
.. only:: subproject and html
diff --git a/Documentation/gpu/vdrm.rst b/Documentation/gpu/vdrm.rst new file mode 100644 index 000000000000..2ab1699c2f42 --- /dev/null +++ b/Documentation/gpu/vdrm.rst @@ -0,0 +1,51 @@ +============================= + drm/vdrm virtual DRM driver +============================= + +Virtual DRM splits the overlay planes of a display controller into multiple +virtual devices to allow each plane to be accessed by each process. + +This makes it possible to overlay images output from multiple processes on a +display. For example, one process displays the camera image without compositor +while another process overlays the UI. + +The virtual DRM creates standalone virtual device and make DRM planes from a +master device (e.g. card0) accessible via one or more virtual device. However, +these plane are no longer accessible from the original device. +Each virtual device (and plane) can be accessed via a separate device file. + +The virtual DRM driver doesn't directly control the display hardware and has +no access to the physical bus. Instead, the virtual DRM driver issues requests +to the standard DRM device driver ("master" driver) when the hardware needs to +be controlled. The master driver is modified to notify the virtual DRM driver +of interrupt events from the display hardware. + +Plane position and size +======================= +The initial position, size and z-position of the plane used in virtual DRM is +specified in the device tree. The position and size of the planes are set as +properties and can be updated. The name of each property is as +follows: +* vdrm_offset_x: x-coordinate of the left-top of the plane on the screen +* vdrm_offset_y: y-coordinate of the left-top of the plane on the screen +* vdrm_width: width of the plane +* vdrm_height: height of the plane + +Virtual DRM Functions Reference +=============================== + +.. kernel-doc:: drivers/gpu/drm/vdrm/vdrm_api.h + :internal: + +.. kernel-doc:: drivers/gpu/drm/vdrm/vdrm_drv.c + :export: + +Driver limitations +================== +1. Each virtual DRM device only supports one plane per CRTC. + +2. Virtual DRM doesn't support hot plug connector. + +3. If virtual DRM has multiple CRTCs, the initial position and size of the + virtual DRM planes is the same for all planes, since they cannot be set + for each plane in the device tree.