drm/virtio: support mapping exported vram

Implement virtgpu specific map_dma_buf callback to support mapping
exported vram object dma-bufs. The dma-buf callback is used directly, as
vram objects don't have backing pages and thus can't implement the
drm_gem_object_funcs.get_sg_table callback.
Signed-off-by: David Stevens <stevensd@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20210813005441.608293-1-stevensd@chromium.orgSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_drv.h

@@ -26,6 +26,7 @@
 #ifndef VIRTIO_DRV_H
 #define VIRTIO_DRV_H
 
+#include <linux/dma-direction.h>
 #include <linux/virtio.h>
 #include <linux/virtio_ids.h>
 #include <linux/virtio_config.h>
@@ -459,4 +460,11 @@ bool virtio_gpu_is_vram(struct virtio_gpu_object *bo);
 int virtio_gpu_vram_create(struct virtio_gpu_device *vgdev,
 			   struct virtio_gpu_object_params *params,
 			   struct virtio_gpu_object **bo_ptr);
+struct sg_table *virtio_gpu_vram_map_dma_buf(struct virtio_gpu_object *bo,
+					     struct device *dev,
+					     enum dma_data_direction dir);
+void virtio_gpu_vram_unmap_dma_buf(struct device *dev,
+				   struct sg_table *sgt,
+				   enum dma_data_direction dir);
+
 #endif

drivers/gpu/drm/virtio/virtgpu_prime.c

@@ -43,13 +43,41 @@ static int virtgpu_virtio_get_uuid(struct dma_buf *buf,
 	return 0;
 }
 
+static struct sg_table *
+virtgpu_gem_map_dma_buf(struct dma_buf_attachment *attach,
+			enum dma_data_direction dir)
+{
+	struct drm_gem_object *obj = attach->dmabuf->priv;
+	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
+
+	if (virtio_gpu_is_vram(bo))
+		return virtio_gpu_vram_map_dma_buf(bo, attach->dev, dir);
+
+	return drm_gem_map_dma_buf(attach, dir);
+}
+
+static void virtgpu_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
+				      struct sg_table *sgt,
+				      enum dma_data_direction dir)
+{
+	struct drm_gem_object *obj = attach->dmabuf->priv;
+	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
+
+	if (virtio_gpu_is_vram(bo)) {
+		virtio_gpu_vram_unmap_dma_buf(attach->dev, sgt, dir);
+		return;
+	}
+
+	drm_gem_unmap_dma_buf(attach, sgt, dir);
+}
+
 static const struct virtio_dma_buf_ops virtgpu_dmabuf_ops =  {
 	.ops = {
 		.cache_sgt_mapping = true,
 		.attach = virtio_dma_buf_attach,
 		.detach = drm_gem_map_detach,
-		.map_dma_buf = drm_gem_map_dma_buf,
-		.unmap_dma_buf = drm_gem_unmap_dma_buf,
+		.map_dma_buf = virtgpu_gem_map_dma_buf,
+		.unmap_dma_buf = virtgpu_gem_unmap_dma_buf,
 		.release = drm_gem_dmabuf_release,
 		.mmap = drm_gem_dmabuf_mmap,
 		.vmap = drm_gem_dmabuf_vmap,

drivers/gpu/drm/virtio/virtgpu_vram.c

 // SPDX-License-Identifier: GPL-2.0
 #include "virtgpu_drv.h"
 
+#include <linux/dma-mapping.h>
+
 static void virtio_gpu_vram_free(struct drm_gem_object *obj)
 {
 	struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
@@ -64,6 +66,65 @@ static int virtio_gpu_vram_mmap(struct drm_gem_object *obj,
 	return ret;
 }
 
+struct sg_table *virtio_gpu_vram_map_dma_buf(struct virtio_gpu_object *bo,
+					     struct device *dev,
+					     enum dma_data_direction dir)
+{
+	struct virtio_gpu_device *vgdev = bo->base.base.dev->dev_private;
+	struct virtio_gpu_object_vram *vram = to_virtio_gpu_vram(bo);
+	struct sg_table *sgt;
+	dma_addr_t addr;
+	int ret;
+
+	sgt = kzalloc(sizeof(*sgt), GFP_KERNEL);
+	if (!sgt)
+		return ERR_PTR(-ENOMEM);
+
+	if (!(bo->blob_flags & VIRTGPU_BLOB_FLAG_USE_MAPPABLE)) {
+		// Virtio devices can access the dma-buf via its UUID. Return a stub
+		// sg_table so the dma-buf API still works.
+		if (!is_virtio_device(dev) || !vgdev->has_resource_assign_uuid) {
+			ret = -EIO;
+			goto out;
+		}
+		return sgt;
+	}
+
+	ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
+	if (ret)
+		goto out;
+
+	addr = dma_map_resource(dev, vram->vram_node.start,
+				vram->vram_node.size, dir,
+				DMA_ATTR_SKIP_CPU_SYNC);
+	ret = dma_mapping_error(dev, addr);
+	if (ret)
+		goto out;
+
+	sg_set_page(sgt->sgl, NULL, vram->vram_node.size, 0);
+	sg_dma_address(sgt->sgl) = addr;
+	sg_dma_len(sgt->sgl) = vram->vram_node.size;
+
+	return sgt;
+out:
+	sg_free_table(sgt);
+	kfree(sgt);
+	return ERR_PTR(ret);
+}
+
+void virtio_gpu_vram_unmap_dma_buf(struct device *dev,
+				   struct sg_table *sgt,
+				   enum dma_data_direction dir)
+{
+	if (sgt->nents) {
+		dma_unmap_resource(dev, sg_dma_address(sgt->sgl),
+				   sg_dma_len(sgt->sgl), dir,
+				   DMA_ATTR_SKIP_CPU_SYNC);
+	}
+	sg_free_table(sgt);
+	kfree(sgt);
+}
+
 static const struct drm_gem_object_funcs virtio_gpu_vram_funcs = {
 	.open = virtio_gpu_gem_object_open,
 	.close = virtio_gpu_gem_object_close,