linux-kernel - [PATCH v3] scsi: ufs: mcq: Limit the amount of inflight requests

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Message-Id: <20230420101116.173-1-avri.altman@wdc.com>
Date:   Thu, 20 Apr 2023 13:11:16 +0300
From:   Avri Altman <avri.altman@....com>
To:     "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Cc:     Asutosh Das <quic_asutoshd@...cinc.com>, quic_cang@...cinc.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johannes Thumshirn <Johannes.Thumshirn@....com>,
        Bart Van Assche <bvanassche@....org>,
        John Garry <john.g.garry@...cle.com>,
        Avri Altman <avri.altman@....com>,
        Johannes Thumshirn <johannes.thumshirn@....com>
Subject: [PATCH v3] scsi: ufs: mcq: Limit the amount of inflight requests

in UFS, each request is designated via the triplet <iid, lun, task tag>.

In UFS4.0 the Initiator ID field is 8 bits wide, comprised of the
EXT_IID and IID fields. Together with the task tag (single byte), they
limit the driver's hw queues capacity.

The purpose of this patch is to document the ufs spec restrictions.
practically, it impose no functional change because a) the current hw
supports much less (merely 64 requests), and b) since shost->host_tagset
is set - then the number of inflight IOs is limited by just the HW queue
depth.

---
v2 -> v3:
fix smatch warnings (Dan Carpenter)
elaborate commit log (John Garry)

v1 -> v2:
Attend Johannes's and Bart's comments

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@....com>
Signed-off-by: Avri Altman <avri.altman@....com>
---
 drivers/ufs/core/ufshcd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 03c47f9a2750..9cebec6be35c 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -8468,6 +8468,12 @@ static int ufshcd_alloc_mcq(struct ufs_hba *hba)
 	if (ret)
 		goto err;
 
+	if (hba->nutrs * hba->nr_hw_queues > SZ_64K - 1) {
+		dev_info(hba->dev, "there can be at most 64K inflight requests\n");
+		ret = -EINVAL;
+		goto err;
+	}
+
 	/*
 	 * Previously allocated memory for nutrs may not be enough in MCQ mode.
 	 * Number of supported tags in MCQ mode may be larger than SDB mode.
-- 
2.17.1