[RFC 4/7] drm/virtio: Import prime buffers from other devices as guest blobs

[Vivek Kasireddy]

By importing scanout buffers from other devices, we should be able
to use the virtio-gpu driver in KMS only mode. Note that we attach
dynamically and register a move_notify() callback so that we can
let the VMM know of any location changes associated with the backing
store of the imported object by sending detach_backing cmd.

Cc: Gerd Hoffmann <kra...@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasire...@intel.com>
---
 drivers/gpu/drm/virtio/virtgpu_prime.c | 54 +++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_prime.c 
b/drivers/gpu/drm/virtio/virtgpu_prime.c
index 1e87dbc9a897..c65dacc1b2b5 100644
--- a/drivers/gpu/drm/virtio/virtgpu_prime.c
+++ b/drivers/gpu/drm/virtio/virtgpu_prime.c
@@ -255,10 +255,36 @@ static int virtgpu_dma_buf_init_obj(struct drm_device 
*dev,
        return ret;
 }
 
+static const struct drm_gem_object_funcs virtgpu_gem_dma_buf_funcs = {
+       .free = virtgpu_dma_buf_free_obj,
+};
+
+static void virtgpu_dma_buf_move_notify(struct dma_buf_attachment *attach)
+{
+       struct drm_gem_object *obj = attach->importer_priv;
+       struct virtio_gpu_device *vgdev = obj->dev->dev_private;
+       struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
+
+       if (bo->created) {
+               virtio_gpu_cmd_resource_detach_backing(vgdev,
+                                                      bo->hw_res_handle);
+               bo->has_backing = false;
+       }
+}
+
+static const struct dma_buf_attach_ops virtgpu_dma_buf_attach_ops = {
+       .allow_peer2peer = true,
+       .move_notify = virtgpu_dma_buf_move_notify
+};
+
 struct drm_gem_object *virtgpu_gem_prime_import(struct drm_device *dev,
                                                struct dma_buf *buf)
 {
+       struct virtio_gpu_device *vgdev = dev->dev_private;
+       struct dma_buf_attachment *attach;
+       struct virtio_gpu_object *bo;
        struct drm_gem_object *obj;
+       int ret;
 
        if (buf->ops == &virtgpu_dmabuf_ops.ops) {
                obj = buf->priv;
@@ -272,7 +298,32 @@ struct drm_gem_object *virtgpu_gem_prime_import(struct 
drm_device *dev,
                }
        }
 
-       return drm_gem_prime_import(dev, buf);
+       if (!vgdev->has_resource_blob || vgdev->has_virgl_3d)
+               return drm_gem_prime_import(dev, buf);
+
+       bo = kzalloc(sizeof(*bo), GFP_KERNEL);
+       if (!bo)
+               return ERR_PTR(-ENOMEM);
+
+       obj = &bo->base.base;
+       obj->funcs = &virtgpu_gem_dma_buf_funcs;
+       drm_gem_private_object_init(dev, obj, buf->size);
+
+       attach = dma_buf_dynamic_attach(buf, dev->dev,
+                                       &virtgpu_dma_buf_attach_ops, obj);
+       if (IS_ERR(attach)) {
+               kfree(bo);
+               return ERR_CAST(attach);
+       }
+
+       obj->import_attach = attach;
+       get_dma_buf(buf);
+
+       ret = virtgpu_dma_buf_init_obj(dev, bo, attach);
+       if (ret < 0)
+               return ERR_PTR(ret);
+
+       return obj;
 }
 
 struct drm_gem_object *virtgpu_gem_prime_import_sg_table(
@@ -281,3 +332,4 @@ struct drm_gem_object *virtgpu_gem_prime_import_sg_table(
 {
        return ERR_PTR(-ENODEV);
 }
+
-- 
2.43.0