1=== 2drm 3=== 4 5------------------------ 6Direct Rendering Manager 7------------------------ 8 9:Date: September 2012 10:Manual section: 7 11:Manual group: Direct Rendering Manager 12 13Synopsis 14======== 15 16``#include <xf86drm.h>`` 17 18Description 19=========== 20 21The *Direct Rendering Manager* (DRM) is a framework to manage *Graphics 22Processing Units* (GPUs). It is designed to support the needs of complex 23graphics devices, usually containing programmable pipelines well suited 24to 3D graphics acceleration. Furthermore, it is responsible for memory 25management, interrupt handling and DMA to provide a uniform interface to 26applications. 27 28In earlier days, the kernel framework was solely used to provide raw 29hardware access to privileged user-space processes which implement all 30the hardware abstraction layers. But more and more tasks were moved into 31the kernel. All these interfaces are based on **ioctl**\ (2) commands on 32the DRM character device. The *libdrm* library provides wrappers for these 33system-calls and many helpers to simplify the API. 34 35When a GPU is detected, the DRM system loads a driver for the detected 36hardware type. Each connected GPU is then presented to user-space via a 37character-device that is usually available as ``/dev/dri/card0`` and can 38be accessed with **open**\ (2) and **close**\ (2). However, it still 39depends on the graphics driver which interfaces are available on these 40devices. If an interface is not available, the syscalls will fail with 41``EINVAL``. 42 43Authentication 44-------------- 45 46All DRM devices provide authentication mechanisms. Only a DRM master is 47allowed to perform mode-setting or modify core state and only one user 48can be DRM master at a time. See **drmSetMaster**\ (3) for information 49on how to become DRM master and what the limitations are. Other DRM users 50can be authenticated to the DRM-Master via **drmAuthMagic**\ (3) so they 51can perform buffer allocations and rendering. 52 53Mode-Setting 54------------ 55 56Managing connected monitors and displays and changing the current modes 57is called *Mode-Setting*. This is restricted to the current DRM master. 58Historically, this was implemented in user-space, but new DRM drivers 59implement a kernel interface to perform mode-setting called *Kernel Mode 60Setting* (KMS). If your hardware-driver supports it, you can use the KMS 61API provided by DRM. This includes allocating framebuffers, selecting 62modes and managing CRTCs and encoders. See **drm-kms**\ (7) for more. 63 64Memory Management 65----------------- 66 67The most sophisticated tasks for GPUs today is managing memory objects. 68Textures, framebuffers, command-buffers and all other kinds of commands 69for the GPU have to be stored in memory. The DRM driver takes care of 70managing all memory objects, flushing caches, synchronizing access and 71providing CPU access to GPU memory. All memory management is hardware 72driver dependent. However, two generic frameworks are available that are 73used by most DRM drivers. These are the *Translation Table Manager* 74(TTM) and the *Graphics Execution Manager* (GEM). They provide generic 75APIs to create, destroy and access buffers from user-space. However, 76there are still many differences between the drivers so driver-depedent 77code is still needed. Many helpers are provided in *libgbm* (Graphics 78Buffer Manager) from the *Mesa* project. For more information on DRM 79memory management, see **drm-memory**\ (7). 80 81Reporting Bugs 82============== 83 84Bugs in this manual should be reported to 85https://gitlab.freedesktop.org/mesa/drm/-/issues. 86 87See Also 88======== 89 90**drm-kms**\ (7), **drm-memory**\ (7), **drmSetMaster**\ (3), 91**drmAuthMagic**\ (3), **drmAvailable**\ (3), **drmOpen**\ (3) 92