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Diffstat (limited to 'Documentation/gpu/drm-mm.rst')
| -rw-r--r-- | Documentation/gpu/drm-mm.rst | 68 |
1 files changed, 31 insertions, 37 deletions
diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst index 59619296c84b..c77b32601260 100644 --- a/Documentation/gpu/drm-mm.rst +++ b/Documentation/gpu/drm-mm.rst @@ -149,19 +149,19 @@ struct :c:type:`struct drm_gem_object <drm_gem_object>`. To create a GEM object, a driver allocates memory for an instance of its specific GEM object type and initializes the embedded struct :c:type:`struct drm_gem_object <drm_gem_object>` with a call -to :c:func:`drm_gem_object_init()`. The function takes a pointer +to drm_gem_object_init(). The function takes a pointer to the DRM device, a pointer to the GEM object and the buffer object size in bytes. GEM uses shmem to allocate anonymous pageable memory. -:c:func:`drm_gem_object_init()` will create an shmfs file of the +drm_gem_object_init() will create an shmfs file of the requested size and store it into the struct :c:type:`struct drm_gem_object <drm_gem_object>` filp field. The memory is used as either main storage for the object when the graphics hardware uses system memory directly or as a backing store otherwise. Drivers are responsible for the actual physical pages allocation by -calling :c:func:`shmem_read_mapping_page_gfp()` for each page. +calling shmem_read_mapping_page_gfp() for each page. Note that they can decide to allocate pages when initializing the GEM object, or to delay allocation until the memory is needed (for instance when a page fault occurs as a result of a userspace memory access or @@ -170,20 +170,18 @@ when the driver needs to start a DMA transfer involving the memory). Anonymous pageable memory allocation is not always desired, for instance when the hardware requires physically contiguous system memory as is often the case in embedded devices. Drivers can create GEM objects with -no shmfs backing (called private GEM objects) by initializing them with -a call to :c:func:`drm_gem_private_object_init()` instead of -:c:func:`drm_gem_object_init()`. Storage for private GEM objects -must be managed by drivers. +no shmfs backing (called private GEM objects) by initializing them with a call +to drm_gem_private_object_init() instead of drm_gem_object_init(). Storage for +private GEM objects must be managed by drivers. GEM Objects Lifetime -------------------- All GEM objects are reference-counted by the GEM core. References can be -acquired and release by :c:func:`calling drm_gem_object_get()` and -:c:func:`drm_gem_object_put()` respectively. The caller must hold the -:c:type:`struct drm_device <drm_device>` struct_mutex lock when calling -:c:func:`drm_gem_object_get()`. As a convenience, GEM provides -:c:func:`drm_gem_object_put_unlocked()` functions that can be called without +acquired and release by calling drm_gem_object_get() and drm_gem_object_put() +respectively. The caller must hold the :c:type:`struct drm_device <drm_device>` +struct_mutex lock when calling drm_gem_object_get(). As a convenience, GEM +provides drm_gem_object_put_unlocked() functions that can be called without holding the lock. When the last reference to a GEM object is released the GEM core calls @@ -194,7 +192,7 @@ free the GEM object and all associated resources. void (\*gem_free_object) (struct drm_gem_object \*obj); Drivers are responsible for freeing all GEM object resources. This includes the resources created by the GEM core, which need to be released with -:c:func:`drm_gem_object_release()`. +drm_gem_object_release(). GEM Objects Naming ------------------ @@ -210,13 +208,11 @@ to the GEM object in other standard or driver-specific ioctls. Closing a DRM file handle frees all its GEM handles and dereferences the associated GEM objects. -To create a handle for a GEM object drivers call -:c:func:`drm_gem_handle_create()`. The function takes a pointer -to the DRM file and the GEM object and returns a locally unique handle. -When the handle is no longer needed drivers delete it with a call to -:c:func:`drm_gem_handle_delete()`. Finally the GEM object -associated with a handle can be retrieved by a call to -:c:func:`drm_gem_object_lookup()`. +To create a handle for a GEM object drivers call drm_gem_handle_create(). The +function takes a pointer to the DRM file and the GEM object and returns a +locally unique handle. When the handle is no longer needed drivers delete it +with a call to drm_gem_handle_delete(). Finally the GEM object associated with a +handle can be retrieved by a call to drm_gem_object_lookup(). Handles don't take ownership of GEM objects, they only take a reference to the object that will be dropped when the handle is destroyed. To @@ -258,7 +254,7 @@ The mmap system call can't be used directly to map GEM objects, as they don't have their own file handle. Two alternative methods currently co-exist to map GEM objects to userspace. The first method uses a driver-specific ioctl to perform the mapping operation, calling -:c:func:`do_mmap()` under the hood. This is often considered +do_mmap() under the hood. This is often considered dubious, seems to be discouraged for new GEM-enabled drivers, and will thus not be described here. @@ -267,23 +263,22 @@ The second method uses the mmap system call on the DRM file handle. void offset); DRM identifies the GEM object to be mapped by a fake offset passed through the mmap offset argument. Prior to being mapped, a GEM object must thus be associated with a fake offset. To do so, drivers -must call :c:func:`drm_gem_create_mmap_offset()` on the object. +must call drm_gem_create_mmap_offset() on the object. Once allocated, the fake offset value must be passed to the application in a driver-specific way and can then be used as the mmap offset argument. -The GEM core provides a helper method :c:func:`drm_gem_mmap()` to +The GEM core provides a helper method drm_gem_mmap() to handle object mapping. The method can be set directly as the mmap file operation handler. It will look up the GEM object based on the offset value and set the VMA operations to the :c:type:`struct drm_driver -<drm_driver>` gem_vm_ops field. Note that -:c:func:`drm_gem_mmap()` doesn't map memory to userspace, but -relies on the driver-provided fault handler to map pages individually. +<drm_driver>` gem_vm_ops field. Note that drm_gem_mmap() doesn't map memory to +userspace, but relies on the driver-provided fault handler to map pages +individually. -To use :c:func:`drm_gem_mmap()`, drivers must fill the struct -:c:type:`struct drm_driver <drm_driver>` gem_vm_ops field -with a pointer to VM operations. +To use drm_gem_mmap(), drivers must fill the struct :c:type:`struct drm_driver +<drm_driver>` gem_vm_ops field with a pointer to VM operations. The VM operations is a :c:type:`struct vm_operations_struct <vm_operations_struct>` made up of several fields, the more interesting ones being: @@ -298,9 +293,8 @@ made up of several fields, the more interesting ones being: The open and close operations must update the GEM object reference -count. Drivers can use the :c:func:`drm_gem_vm_open()` and -:c:func:`drm_gem_vm_close()` helper functions directly as open -and close handlers. +count. Drivers can use the drm_gem_vm_open() and drm_gem_vm_close() helper +functions directly as open and close handlers. The fault operation handler is responsible for mapping individual pages to userspace when a page fault occurs. Depending on the memory @@ -312,12 +306,12 @@ Drivers that want to map the GEM object upfront instead of handling page faults can implement their own mmap file operation handler. For platforms without MMU the GEM core provides a helper method -:c:func:`drm_gem_cma_get_unmapped_area`. The mmap() routines will call -this to get a proposed address for the mapping. +drm_gem_cma_get_unmapped_area(). The mmap() routines will call this to get a +proposed address for the mapping. -To use :c:func:`drm_gem_cma_get_unmapped_area`, drivers must fill the -struct :c:type:`struct file_operations <file_operations>` get_unmapped_area -field with a pointer on :c:func:`drm_gem_cma_get_unmapped_area`. +To use drm_gem_cma_get_unmapped_area(), drivers must fill the struct +:c:type:`struct file_operations <file_operations>` get_unmapped_area field with +a pointer on drm_gem_cma_get_unmapped_area(). More detailed information about get_unmapped_area can be found in Documentation/nommu-mmap.txt |