DRM 的Property IN_FENCE_FD和OUT_FENCE_PTR使用示例

Property IN_FENCE_FD 和 OUT_FENCE_PTR 都是在 DRM 中用于同步的属性，它们可以用于确保输入和输出的同步信号已经准备就绪。

下面是一个示例代码，展示了如何使用 IN_FENCE_FD 和 OUT_FENCE_PTR 属性：

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <drm/drm.h>
#include <drm/drm_mode.h>

int main() {
    int fd;
    struct drm_mode_create_dumb create_dumb;
    struct drm_mode_map_dumb map_dumb;
    struct drm_mode_fb_cmd cmd;
    struct drm_gem_close gem_close;
    struct drm_mode_atomic atomic;
    struct drm_event_fence event_fence;
    
    // 打开 DRM 设备
    fd = open("/dev/dri/card0", O_RDWR);
    
    // 创建 input dumb buffer
    create_dumb.width = 800;
    create_dumb.height = 600;
    create_dumb.bpp = 32;
    ioctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb);
    
    // 映射 input dumb buffer
    map_dumb.handle = create_dumb.handle;
    ioctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb);
    
    // 配置 input framebuffer
    cmd.fb_id = 0;
    cmd.width = create_dumb.width;
    cmd.height = create_dumb.height;
    cmd.pitch = create_dumb.pitch;
    cmd.bpp = create_dumb.bpp;
    cmd.depth = 24;
    cmd.handle = create_dumb.handle;
    ioctl(fd, DRM_IOCTL_MODE_ADDFB, &cmd);
    
    // 准备输入同步信号
    int in_fence_fd = fence_create(fd, 0);
    
    // 创建 output dumb buffer
    create_dumb.width = 800;
    create_dumb.height = 600;
    create_dumb.bpp = 32;
    ioctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb);
    
    // 映射 output dumb buffer
    map_dumb.handle = create_dumb.handle;
    ioctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb);
    
    // 配置 output framebuffer
    cmd.fb_id = 0;
    cmd.width = create_dumb.width;
    cmd.height = create_dumb.height;
    cmd.pitch = create_dumb.pitch;
    cmd.bpp = create_dumb.bpp;
    cmd.depth = 24;
    cmd.handle = create_dumb.handle;
    ioctl(fd, DRM_IOCTL_MODE_ADDFB, &cmd);
    
    // 准备输出同步信号
    struct drm_mode_syncobj_create out_syncobj;
    out_syncobj.handle = 0;
    ioctl(fd, DRM_IOCTL_MODE_CREATE_SYNCOBJ, &out_syncobj);
    
    // 提交 buffer，并设置 IN_FENCE_FD 和 OUT_FENCE_PTR
    atomic.fb_ids_ptr = (uint64_t) &cmd.fb_id;
    atomic.crtc_id = 0;
    atomic.connector_id = 0;
    atomic.count_props = 1;
    atomic.user_data = 0;
    atomic.flags = DRM_MODE_ATOMIC_NONBLOCK | DRM_MODE_PAGE_FLIP_EVENT | DRM_MODE_ATOMIC_ALLOW_MODESET;
    atomic.objs_ptr = (uint64_t) &cmd.fb_id;
    atomic.objs = 1;
    atomic.fence_fd = in_fence_fd;  // 设置 IN_FENCE_FD
    atomic.out_fence_ptr = (uint64_t) &out_syncobj.handle;  // 设置 OUT_FENCE_PTR
    
    ioctl(fd, DRM_IOCTL_MODE_ATOMIC, &atomic);
    
    // 等待输入同步信号
    read(in_fence_fd, &event_fence, sizeof(event_fence));
    
    // 等待输出同步信号
    struct drm_mode_syncobj_wait wait;
    wait.handles = (uint64_t) &out_syncobj.handle;
    wait.count_handles = 1;
    wait.timeout_nsec = 0;
    ioctl(fd, DRM_IOCTL_MODE_SYNCOBJ_WAIT, &wait);
    
    // 关闭输入 fence 文件描述符
    close(in_fence_fd);
    
    // 关闭输出同步对象
    struct drm_mode_syncobj_destroy out_syncobj_destroy;
    out_syncobj_destroy.handle = out_syncobj.handle;
    ioctl(fd, DRM_IOCTL_MODE_DESTROY_SYNCOBJ, &out_syncobj_destroy);
    
    // 关闭 output framebuffer
    ioctl(fd, DRM_IOCTL_MODE_RMFB, &cmd.fb_id);
    
    // 关闭 output dumb buffer
    gem_close.handle = create_dumb.handle;
    ioctl(fd, DRM_IOCTL_GEM_CLOSE, &gem_close);
    
    // 关闭 input framebuffer
    ioctl(fd, DRM_IOCTL_MODE_RMFB, &cmd.fb_id);
    
    // 关闭 input dumb buffer
    gem_close.handle = create_dumb.handle;
    ioctl(fd, DRM_IOCTL_GEM_CLOSE, &gem_close);
    
    // 关闭 DRM 设备
    close(fd);
    
    return 0;
}

该示例代码演示了如何使用 IN_FENCE_FD 和 OUT_FENCE_PTR 属性来实现输入和输出的同步。在提交 framebuffer 时，设置 IN_FENCE_FD 属性以确保输入同步信号已经准备就绪，并设置 OUT_FENCE_PTR 属性以获取输出同步信号。请注意，这只是一个简单的示例，实际使用时可能需要根据具体需求进行修改和扩展。