linux-kernel - [PATCH v2] scsi: ufs: mcq: Limit the amount of inflight requests

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Message-Id: <20230331074650.75-1-avri.altman@wdc.com>
Date:   Fri, 31 Mar 2023 10:46:50 +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>,
        Avri Altman <avri.altman@....com>
Subject: [PATCH v2] 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.

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

Signed-off-by: Avri Altman <avri.altman@....com>
---
 drivers/ufs/core/ufshcd.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 35a3bd95c5e4..cac7c9918c5b 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -8468,6 +8468,11 @@ 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");
+		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