DRM系列(8)之prepare_signaling

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 《Linux图形驱动与桌面》专栏地址：Linux图形驱动与桌面

回顾一下commit的关键：

1、drm_atomic_set_property(state, file_priv, vobj, prop, prop_value)
2、prepare_signalng(dev, state, arg, file_priv, &fence_state, &num_fences)
3、drm_atomic_nonblocking_commit/drm_atomic_commit
4、complete_signaling(dev, state, fence_state, num_fences, !ret)

prepare_signaling完成了三大步：

1. 构造了drm_pending_vblank_event对象，关联crtc

2. 设置crtc的fence

3. 设置connector的fence

传入的参数：

static int prepare_signaling(struct drm_device *dev,