scsi: hisi_sas: Limit max hw sectors for v3 HW

If the controller is behind an IOMMU then the IOMMU IOVA caching range can
affect performance, as discussed in [0].

Limit the max HW sectors to not exceed this limit. We need to hardcode the
value until a proper DMA mapping API is available.

[0] https://lore.kernel.org/linux-iommu/[email protected]/

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: John Garry <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: John Garry

drivers/scsi/hisi_sas/hisi_sas_v3_hw.c

@@ -2782,6 +2782,7 @@ static int slave_configure_v3_hw(struct scsi_device *sdev)
 	struct hisi_hba *hisi_hba = shost_priv(shost);
 	struct device *dev = hisi_hba->dev;
 	int ret = sas_slave_configure(sdev);
+	unsigned int max_sectors;
 
 	if (ret)
 		return ret;
@@ -2799,6 +2800,12 @@ static int slave_configure_v3_hw(struct scsi_device *sdev)
 		}
 	}
 
+	/* Set according to IOMMU IOVA caching limit */
+	max_sectors = min_t(size_t, queue_max_hw_sectors(sdev->request_queue),
+			    (PAGE_SIZE * 32) >> SECTOR_SHIFT);
+
+	blk_queue_max_hw_sectors(sdev->request_queue, max_sectors);
+
 	return 0;
 }