RDMA/srp: Increase max_segment_size

The default behavior of the SCSI core is to set the block layer request
queue parameter max_segment_size to 64 KB. That means that elements of
scatterlists are limited to 64 KB. Since RDMA adapters support larger
sizes, increase max_segment_size for the SRP initiator.

Notes:
- The SCSI max_segment_size parameter was introduced in kernel v5.0. See
  also commit 50c2e9107f17 ("scsi: introduce a max_segment_size
  host_template parameters").
- Some other block drivers already set max_segment_size to UINT_MAX,
  e.g. nbd and rbd.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 94b6e1dd4dab..71ea144ec823 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -3716,6 +3716,19 @@ static inline unsigned int ib_sg_dma_len(struct ib_device *dev,
 }
 
 /**
+ * ib_dma_max_seg_size - Return the size limit of a single DMA transfer
+ * @dev: The device to query
+ *
+ * The returned value represents a size in bytes.
+ */
+static inline unsigned int ib_dma_max_seg_size(struct ib_device *dev)
+{
+	struct device_dma_parameters *p = dev->dma_device->dma_parms;
+
+	return p ? p->max_segment_size : UINT_MAX;
+}
+
+/**
  * ib_dma_sync_single_for_cpu - Prepare DMA region to be accessed by CPU
  * @dev: The device for which the DMA address was created
  * @addr: The DMA address