mirror of https://gitee.com/openkylin/linux.git
95 lines
3.4 KiB
C
95 lines
3.4 KiB
C
// 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");
|