respectively. The conversion is handled by the DRM core without any
driver-specific support.
</para>
- <para>
- Similar to global names, GEM file descriptors are also used to share GEM
- objects across processes. They offer additional security: as file
- descriptors must be explicitly sent over UNIX domain sockets to be shared
- between applications, they can't be guessed like the globally unique GEM
- names.
- </para>
- <para>
- Drivers that support GEM file descriptors, also known as the DRM PRIME
- API, must set the DRIVER_PRIME bit in the struct
- <structname>drm_driver</structname>
- <structfield>driver_features</structfield> field, and implement the
- <methodname>prime_handle_to_fd</methodname> and
- <methodname>prime_fd_to_handle</methodname> operations.
- </para>
- <para>
- <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
- struct drm_file *file_priv, uint32_t handle,
- uint32_t flags, int *prime_fd);
- int (*prime_fd_to_handle)(struct drm_device *dev,
- struct drm_file *file_priv, int prime_fd,
- uint32_t *handle);</synopsis>
- Those two operations convert a handle to a PRIME file descriptor and
- vice versa. Drivers must use the kernel dma-buf buffer sharing framework
- to manage the PRIME file descriptors.
- </para>
- <para>
- While non-GEM drivers must implement the operations themselves, GEM
- drivers must use the <function>drm_gem_prime_handle_to_fd</function>
- and <function>drm_gem_prime_fd_to_handle</function> helper functions.
- Those helpers rely on the driver
- <methodname>gem_prime_export</methodname> and
- <methodname>gem_prime_import</methodname> operations to create a dma-buf
- instance from a GEM object (dma-buf exporter role) and to create a GEM
- object from a dma-buf instance (dma-buf importer role).
- </para>
- <para>
- <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
- struct drm_gem_object *obj,
- int flags);
- struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
- struct dma_buf *dma_buf);</synopsis>
- These two operations are mandatory for GEM drivers that support DRM
- PRIME.
- </para>
- <sect4>
- <title>DRM PRIME Helper Functions Reference</title>
-!Pdrivers/gpu/drm/drm_prime.c PRIME Helpers
- </sect4>
+ <para>
+ GEM also supports buffer sharing with dma-buf file descriptors through
+ PRIME. GEM-based drivers must use the provided helpers functions to
+ implement the exporting and importing correctly. See <xref linkend="drm-prime-support" />.
+ Since sharing file descriptors is inherently more secure than the
+ easily guessable and global GEM names it is the preferred buffer
+ sharing mechanism. Sharing buffers through GEM names is only supported
+ for legacy userspace. Furthermore PRIME also allows cross-device
+ buffer sharing since it is based on dma-bufs.
+ </para>
</sect3>
<sect3 id="drm-gem-objects-mapping">
<title>GEM Objects Mapping</title>
abstracted from the client in libdrm.
</para>
</sect3>
- <sect2>
+ <sect3>
<title>GEM Function Reference</title>
!Edrivers/gpu/drm/drm_gem.c
- </sect2>
+ </sect3>
</sect2>
<sect2>
<title>VMA Offset Manager</title>
!Edrivers/gpu/drm/drm_vma_manager.c
!Iinclude/drm/drm_vma_manager.h
</sect2>
+ <sect2 id="drm-prime-support">
+ <title>PRIME Buffer Sharing</title>
+ <para>
+ PRIME is the cross device buffer sharing framework in drm, originally
+ created for the OPTIMUS range of multi-gpu platforms. To userspace
+ PRIME buffers are dma-buf based file descriptors.
+ </para>
+ <sect3>
+ <title>Overview and Driver Interface</title>
+ <para>
+ Similar to GEM global names, PRIME file descriptors are
+ also used to share buffer objects across processes. They offer
+ additional security: as file descriptors must be explicitly sent over
+ UNIX domain sockets to be shared between applications, they can't be
+ guessed like the globally unique GEM names.
+ </para>
+ <para>
+ Drivers that support the PRIME
+ API must set the DRIVER_PRIME bit in the struct
+ <structname>drm_driver</structname>
+ <structfield>driver_features</structfield> field, and implement the
+ <methodname>prime_handle_to_fd</methodname> and
+ <methodname>prime_fd_to_handle</methodname> operations.
+ </para>
+ <para>
+ <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
+ struct drm_file *file_priv, uint32_t handle,
+ uint32_t flags, int *prime_fd);
+int (*prime_fd_to_handle)(struct drm_device *dev,
+ struct drm_file *file_priv, int prime_fd,
+ uint32_t *handle);</synopsis>
+ Those two operations convert a handle to a PRIME file descriptor and
+ vice versa. Drivers must use the kernel dma-buf buffer sharing framework
+ to manage the PRIME file descriptors. Similar to the mode setting
+ API PRIME is agnostic to the underlying buffer object manager, as
+ long as handles are 32bit unsinged integers.
+ </para>
+ <para>
+ While non-GEM drivers must implement the operations themselves, GEM
+ drivers must use the <function>drm_gem_prime_handle_to_fd</function>
+ and <function>drm_gem_prime_fd_to_handle</function> helper functions.
+ Those helpers rely on the driver
+ <methodname>gem_prime_export</methodname> and
+ <methodname>gem_prime_import</methodname> operations to create a dma-buf
+ instance from a GEM object (dma-buf exporter role) and to create a GEM
+ object from a dma-buf instance (dma-buf importer role).
+ </para>
+ <para>
+ <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
+ struct drm_gem_object *obj,
+ int flags);
+struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
+ struct dma_buf *dma_buf);</synopsis>
+ These two operations are mandatory for GEM drivers that support
+ PRIME.
+ </para>
+ </sect3>
+ <sect3>
+ <title>PRIME Helper Functions</title>
+!Pdrivers/gpu/drm/drm_prime.c PRIME Helpers
+ </sect3>
+ </sect2>
+ <sect2>
+ <title>PRIME Function References</title>
+!Edrivers/gpu/drm/drm_prime.c
+ </sect2>
</sect1>
<!-- Internals: mode setting -->
projects / firefly-linux-kernel-4.4.55.git / blobdiff