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DRM(7) Direct Rendering Manager DRM(7) NAME drm - Direct Rendering Manager SYNOPSIS #include <xf86drm.h> DESCRIPTION The Direct Rendering Manager (DRM) is a framework to manage Graphics Pro- cessing Units (GPUs). It is designed to support the needs of complex graph- ics devices, usually containing programmable pipelines well suited to 3D graphics acceleration. Furthermore, it is responsible for memory manage- ment, interrupt handling and DMA to provide a uniform interface to applica- tions. In earlier days, the kernel framework was solely used to provide raw hard- ware access to privileged user-space processes which implement all the hardware abstraction layers. But more and more tasks were moved into the kernel. All these interfaces are based on ioctl(2) commands on the DRM character device. The libdrm library provides wrappers for these sys- tem-calls and many helpers to simplify the API. When a GPU is detected, the DRM system loads a driver for the detected hardware type. Each connected GPU is then presented to user-space via a character-device that is usually available as /dev/dri/card0 and can be ac- cessed with open(2) and close(2). However, it still depends on the graphics driver which interfaces are available on these devices. If an interface is not available, the syscalls will fail with EINVAL. Authentication All DRM devices provide authentication mechanisms. Only a DRM master is al- lowed to perform mode-setting or modify core state and only one user can be DRM master at a time. See drmSetMaster(3) for information on how to become DRM master and what the limitations are. Other DRM users can be authenti- cated to the DRM-Master via drmAuthMagic(3) so they can perform buffer al- locations and rendering. Mode-Setting Managing connected monitors and displays and changing the current modes is called Mode-Setting. This is restricted to the current DRM master. Histor- ically, this was implemented in user-space, but new DRM drivers implement a kernel interface to perform mode-setting called Kernel Mode Setting (KMS). If your hardware-driver supports it, you can use the KMS API provided by DRM. This includes allocating framebuffers, selecting modes and managing CRTCs and encoders. See drm-kms(7) for more. Memory Management The most sophisticated tasks for GPUs today is managing memory objects. Textures, framebuffers, command-buffers and all other kinds of commands for the GPU have to be stored in memory. The DRM driver takes care of managing all memory objects, flushing caches, synchronizing access and providing CPU access to GPU memory. All memory management is hardware driver dependent. However, two generic frameworks are available that are used by most DRM drivers. These are the Translation Table Manager (TTM) and the Graphics Ex- ecution Manager (GEM). They provide generic APIs to create, destroy and ac- cess buffers from user-space. However, there are still many differences be- tween the drivers so driver-dependent code is still needed. Many helpers are provided in libgbm (Graphics Buffer Manager) from the Mesa project. For more information on DRM memory management, see drm-memory(7). REPORTING BUGS Bugs in this manual should be reported to <https://gitlab.freedesktop.org/mesa/libdrm/-/issues> . SEE ALSO drm-kms(7), drm-memory(7), drmSetMaster(3), drmAuthMagic(3), drmAvail- able(3), drmOpen(3) September 2012 DRM(7)
NAME | SYNOPSIS | DESCRIPTION | REPORTING BUGS | SEE ALSO
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