[RFC PATCH v4 1/2] RDMA/umem: Change for rdma devices has not dma device

[Shunsuke Mie]

Current implementation requires a dma device for RDMA driver to use
dma-buf memory space as RDMA buffer. However, software RDMA drivers has
not dma device and copy RDMA data using CPU instead of hardware.

This patch changes to be hold a dma-buf on struct ib_umem_dmabuf. This
allows the software RDMA driver to map dma-buf memory for CPU memory
accessing.

Signed-off-by: Shunsuke Mie <mie at igel.co.jp>
---
 drivers/infiniband/core/umem_dmabuf.c | 20 ++++++++++++++++----
 include/rdma/ib_umem.h                |  1 +
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/infiniband/core/umem_dmabuf.c b/drivers/infiniband/core/umem_dmabuf.c
index e824baf4640d..ebbb0a259fd4 100644
--- a/drivers/infiniband/core/umem_dmabuf.c
+++ b/drivers/infiniband/core/umem_dmabuf.c
@@ -117,9 +117,6 @@ struct ib_umem_dmabuf *ib_umem_dmabuf_get(struct ib_device *device,
 	if (check_add_overflow(offset, (unsigned long)size, &end))
 		return ret;
 
-	if (unlikely(!ops || !ops->move_notify))
-		return ret;
-
 	dmabuf = dma_buf_get(fd);
 	if (IS_ERR(dmabuf))
 		return ERR_CAST(dmabuf);
@@ -133,6 +130,8 @@ struct ib_umem_dmabuf *ib_umem_dmabuf_get(struct ib_device *device,
 		goto out_release_dmabuf;
 	}
 
+	umem_dmabuf->dmabuf = dmabuf;
+
 	umem = &umem_dmabuf->umem;
 	umem->ibdev = device;
 	umem->length = size;
@@ -143,6 +142,13 @@ struct ib_umem_dmabuf *ib_umem_dmabuf_get(struct ib_device *device,
 	if (!ib_umem_num_pages(umem))
 		goto out_free_umem;
 
+	/* Software RDMA drivers has not dma device. Just get dmabuf from fd */
+	if (!device->dma_device)
+		goto done;
+
+	if (unlikely(!ops || !ops->move_notify))
+		goto out_free_umem;
+
 	umem_dmabuf->attach = dma_buf_dynamic_attach(
 					dmabuf,
 					device->dma_device,
@@ -152,6 +158,7 @@ struct ib_umem_dmabuf *ib_umem_dmabuf_get(struct ib_device *device,
 		ret = ERR_CAST(umem_dmabuf->attach);
 		goto out_free_umem;
 	}
+done:
 	return umem_dmabuf;
 
 out_free_umem:
@@ -165,13 +172,18 @@ EXPORT_SYMBOL(ib_umem_dmabuf_get);
 
 void ib_umem_dmabuf_release(struct ib_umem_dmabuf *umem_dmabuf)
 {
-	struct dma_buf *dmabuf = umem_dmabuf->attach->dmabuf;
+	struct dma_buf *dmabuf = umem_dmabuf->dmabuf;
+
+	if (!umem_dmabuf->attach)
+		goto free_dmabuf;
 
 	dma_resv_lock(dmabuf->resv, NULL);
 	ib_umem_dmabuf_unmap_pages(umem_dmabuf);
 	dma_resv_unlock(dmabuf->resv);
 
 	dma_buf_detach(dmabuf, umem_dmabuf->attach);
+
+free_dmabuf:
 	dma_buf_put(dmabuf);
 	kfree(umem_dmabuf);
 }
diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
index 5ae9dff74dac..11c0cf7e0dd8 100644
--- a/include/rdma/ib_umem.h
+++ b/include/rdma/ib_umem.h
@@ -32,6 +32,7 @@ struct ib_umem {
 struct ib_umem_dmabuf {
 	struct ib_umem umem;
 	struct dma_buf_attachment *attach;
+	struct dma_buf *dmabuf;
 	struct sg_table *sgt;
 	struct scatterlist *first_sg;
 	struct scatterlist *last_sg;
-- 
2.17.1