05166be26d
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128 lines
3.6 KiB
Groff
128 lines
3.6 KiB
Groff
.\" automatically generated with docbook2mdoc drm.xml
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.Dd September 2012
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.Dt DRM 7
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.Os
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.Sh NAME
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.Nm drm
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.Nd Direct Rendering Manager
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.Sh SYNOPSIS
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.Fd #include <xf86drm.h>
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.Sh DESCRIPTION
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The
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.Em Direct Rendering Manager
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(DRM) is a framework
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to manage
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.Em Graphics Processing Units
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(GPUs). It is
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designed to support the needs of complex graphics devices, usually
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containing programmable pipelines well suited to 3D graphics
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acceleration.
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Furthermore, it is responsible for memory management,
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interrupt handling and DMA to provide a uniform interface to
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applications.
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.Pp
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In earlier days, the kernel framework was solely used to provide raw
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hardware access to privileged user-space processes which implement
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all the hardware abstraction layers.
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But more and more tasks were
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moved into the kernel.
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All these interfaces are based on
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.Xr ioctl 2
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commands on the DRM character device.
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The
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.Em libdrm
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library provides wrappers for these system-calls and many helpers to
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simplify the API.
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.Pp
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When a GPU is detected, the DRM system loads a driver for the detected
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hardware type.
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Each connected GPU is then presented to user-space via
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a character-device that is usually available as
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.Pa /dev/drm0
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and can be accessed with
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.Xr open 2
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and
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.Xr close 2 .
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However, it still depends on the graphics driver which interfaces are
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available on these devices.
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If an interface is not available, the
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syscalls will fail with
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.Ql EINVAL .
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.Ss Authentication
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All DRM devices provide authentication mechanisms.
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Only a DRM-Master
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is allowed to perform mode-setting or modify core state and only one
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user can be DRM-Master at a time.
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See
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.Xr drmSetMaster 3
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for information on how to become DRM-Master and what the limitations
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are.
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Other DRM users can be authenticated to the DRM-Master via
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.Xr drmAuthMagic 3
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so they can perform buffer allocations and rendering.
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.Ss Mode-Setting
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Managing connected monitors and displays and changing the current
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modes is called
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.Em Mode-Setting .
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This is
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restricted to the current DRM-Master.
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Historically, this was
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implemented in user-space, but new DRM drivers implement a kernel
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interface to perform mode-setting called
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.Em Kernel Mode Setting
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(KMS). If your
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hardware-driver supports it, you can use the KMS API provided by
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DRM.
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This includes allocating framebuffers, selecting modes and
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managing CRTCs and encoders.
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See
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.Xr drm-kms 7
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for more.
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.Ss Memory Management
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The most sophisticated tasks for GPUs today is managing memory
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objects.
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Textures, framebuffers, command-buffers and all other kinds
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of commands for the GPU have to be stored in memory.
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The DRM driver
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takes care of managing all memory objects, flushing caches,
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synchronizing access and providing CPU access to GPU memory.
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All
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memory management is hardware driver dependent.
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However, two generic
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frameworks are available that are used by most DRM drivers.
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These
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are the
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.Em Translation Table Manager
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(TTM) and the
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.Em Graphics Execution Manager
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(GEM). They provide
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generic APIs to create, destroy and access buffers from user-space.
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However, there are still many differences between the drivers so
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driver-depedent code is still needed.
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Many helpers are provided in
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.Em libgbm
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(Graphics Buffer Manager) from the
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.Em mesa-project .
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For more information on DRM
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memory-management, see
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.Xr drm-memory 7 .
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.Sh REPORTING BUGS
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Bugs in this manual should be reported to
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https://bugs.freedesktop.org/enter_bug.cgi?product=DRI&component=libdrm
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under the "DRI" product, component "libdrm"
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.Sh SEE ALSO
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.Xr drm-kms 7 ,
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.Xr drm-memory 7 ,
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.Xr drmSetMaster 3 ,
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.Xr drmAuthMagic 3 ,
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.Xr drmAvailable 3 ,
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.Xr drmOpen 3
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.Sh AUTHORS
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.An -nosplit
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.Sy Direct Rendering Manager
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.Pp
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.Sy libdrm
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.An -split
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Developer:
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.An David Herrmann Aq Mt dh.herrmann@googlemail.com
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