linux-kernel - [PATCH AUTOSEL 5.15 08/18] scsi: hisi_sas: Limit max hw sectors for v3 HW

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Message-Id: <20220706153153.1598076-8-sashal@kernel.org>
Date:   Wed,  6 Jul 2022 11:31:43 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     John Garry <john.garry@...wei.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Sasha Levin <sashal@...nel.org>, jejb@...ux.ibm.com,
        linux-scsi@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 08/18] scsi: hisi_sas: Limit max hw sectors for v3 HW

From: John Garry <john.garry@...wei.com>

[ Upstream commit fce54ed027577517df1e74b7d54dc2b1bd536887 ]

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/20210129092120.1482-1-thunder.leizhen@huawei.com/

Link: https://lore.kernel.org/r/1655988119-223714-1-git-send-email-john.garry@huawei.com
Signed-off-by: John Garry <john.garry@...wei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/scsi/hisi_sas/hisi_sas_v3_hw.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
index 1f5e0688c0c8..15c7451fb30f 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
@@ -2758,6 +2758,7 @@ 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;
@@ -2775,6 +2776,12 @@ 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;
 }
 
-- 
2.35.1