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// SPDX-License-Identifier: GPL-2.0-or-later
#include <linux/module.h>
/**
* DOC: overview
*
* This library provides &struct drm_gem_vram_object (GEM VRAM), a GEM
* buffer object that is backed by video RAM. It can be used for
* framebuffer devices with dedicated memory. The video RAM is managed
* by &struct drm_vram_mm (VRAM MM).
*
* With the GEM interface userspace applications create, manage and destroy
* graphics buffers, such as an on-screen framebuffer. GEM does not provide
* an implementation of these interfaces. It's up to the DRM driver to
* provide an implementation that suits the hardware. If the hardware device
* contains dedicated video memory, the DRM driver can use the VRAM helper
* library. Each active buffer object is stored in video RAM. Active
* buffer are used for drawing the current frame, typically something like
* the frame's scanout buffer or the cursor image. If there's no more space
* left in VRAM, inactive GEM objects can be moved to system memory.
*
* The easiest way to use the VRAM helper library is to call
* drm_vram_helper_alloc_mm(). The function allocates and initializes an
* instance of &struct drm_vram_mm in &struct drm_device.vram_mm . Use
* &DRM_GEM_VRAM_DRIVER to initialize &struct drm_driver and
* &DRM_VRAM_MM_FILE_OPERATIONS to initialize &struct file_operations;
* as illustrated below.
*
* .. code-block:: c
*
* struct file_operations fops ={
* .owner = THIS_MODULE,
* DRM_VRAM_MM_FILE_OPERATION
* };
* struct drm_driver drv = {
* .driver_feature = DRM_ ... ,
* .fops = &fops,
* DRM_GEM_VRAM_DRIVER
* };
*
* int init_drm_driver()
* {
* struct drm_device *dev;
* uint64_t vram_base;
* unsigned long vram_size;
* int ret;
*
* // setup device, vram base and size
* // ...
*
* ret = drm_vram_helper_alloc_mm(dev, vram_base, vram_size);
* if (ret)
* return ret;
* return 0;
* }
*
* This creates an instance of &struct drm_vram_mm, exports DRM userspace
* interfaces for GEM buffer management and initializes file operations to
* allow for accessing created GEM buffers. With this setup, the DRM driver
* manages an area of video RAM with VRAM MM and provides GEM VRAM objects
* to userspace.
*
* To clean up the VRAM memory management, call drm_vram_helper_release_mm()
* in the driver's clean-up code.
*
* .. code-block:: c
*
* void fini_drm_driver()
* {
* struct drm_device *dev = ...;
*
* drm_vram_helper_release_mm(dev);
* }
*
* For drawing or scanout operations, buffer object have to be pinned in video
* RAM. Call drm_gem_vram_pin() with &DRM_GEM_VRAM_PL_FLAG_VRAM or
* &DRM_GEM_VRAM_PL_FLAG_SYSTEM to pin a buffer object in video RAM or system
* memory. Call drm_gem_vram_unpin() to release the pinned object afterwards.
*
* A buffer object that is pinned in video RAM has a fixed address within that
* memory region. Call drm_gem_vram_offset() to retrieve this value. Typically
* it's used to program the hardware's scanout engine for framebuffers, set
* the cursor overlay's image for a mouse cursor, or use it as input to the
* hardware's draing engine.
*
* To access a buffer object's memory from the DRM driver, call
* drm_gem_vram_kmap(). It (optionally) maps the buffer into kernel address
* space and returns the memory address. Use drm_gem_vram_kunmap() to
* release the mapping.
*/
MODULE_DESCRIPTION("DRM VRAM memory-management helpers");
MODULE_LICENSE("GPL");
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