On Sat, Jul 3, 2021 at 2:28 AM Sagi Grimberg [off-list ref] wrote:

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From: Dean Balandin <redacted>
In this patch, we present the IO level functionality.

[..]

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+static void nvme_tcp_ofld_set_sg_null(struct nvme_command *c)
+{
+       struct nvme_sgl_desc *sg = &c->common.dptr.sgl;
+       sg->addr = 0;

ok

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+       sg->length = 0;
+       sg->type = (NVME_TRANSPORT_SGL_DATA_DESC << 4) |
+                       NVME_SGL_FMT_TRANSPORT_A;

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+inline void nvme_tcp_ofld_set_sg_inline(struct nvme_tcp_ofld_queue *queue,
+                                       struct nvme_command *c, u32 data_len)
+{
+       struct nvme_sgl_desc *sg = &c->common.dptr.sgl;
+       sg->addr = cpu_to_le64(queue->ctrl->nctrl.icdoff);

ok, what about dma mapping of the address?

The dma mapping is done by the offload device driver.
patch 18 - "qedn: Add IO level fastpath functionality", in qedn_init_sgl().

The dma mapping can and should be done by the nvme/tcp driver. E.g in a similar
manner fow how it's done for nvme/rdma, you can take a look on the code there.

I agree here, the fact that the lld calls blk_rq_map_sg is very much
backwards... If the lld is peeking into a block layer request or bio,
its a sign that the layering is wrong...

Making things more precise while looking in the patch set we were
running here over
the last year, blk_rq_map_sg indeed is called by the nvme driver, and then
dma_map_sg by the hw driver. This is slightly different from the rdma case.

overall, the sequence of calls is the following

sg_alloc_table_chained()
blk_rq_map_sg()
dma_map_sg()

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