linux-kernel - [PATCH v1 1/1] ufs: mcq: Fix the variable wraparound logic

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Message-ID: <e6e8559eee9626afa38f88e18080398e7296e1bb.1685617541.git.quic_nguyenb@quicinc.com>
Date:   Thu, 1 Jun 2023 04:27:01 -0700
From:   "Bao D. Nguyen" <quic_nguyenb@...cinc.com>
To:     <quic_asutoshd@...cinc.com>, <quic_cang@...cinc.com>,
        <bvanassche@....org>, <mani@...nel.org>,
        <stanley.chu@...iatek.com>, <adrian.hunter@...el.com>,
        <beanhuo@...ron.com>, <avri.altman@....com>,
        <martin.petersen@...cle.com>
CC:     <linux-scsi@...r.kernel.org>,
        "Bao D. Nguyen" <quic_nguyenb@...cinc.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Alice Chao <alice.chao@...iatek.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: [PATCH v1 1/1] ufs: mcq: Fix the variable wraparound logic

If the hwq's queue depth is not a multiple of 4s, the
logic used for wrapping around the increase-by-1 sq_head_slot
variable in ufshcd_mcq_sqe_search() will give an incorrect
result because the binary expression of the mask is not
a uniform of all 1s.

Signed-off-by: Bao D. Nguyen <quic_nguyenb@...cinc.com>
---
 drivers/ufs/core/ufs-mcq.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/ufs/core/ufs-mcq.c b/drivers/ufs/core/ufs-mcq.c
index 66ac02e..8e5bc88 100644
--- a/drivers/ufs/core/ufs-mcq.c
+++ b/drivers/ufs/core/ufs-mcq.c
@@ -585,7 +585,6 @@ static bool ufshcd_mcq_sqe_search(struct ufs_hba *hba,
 {
 	struct ufshcd_lrb *lrbp = &hba->lrb[task_tag];
 	struct utp_transfer_req_desc *utrd;
-	u32 mask = hwq->max_entries - 1;
 	__le64  cmd_desc_base_addr;
 	bool ret = false;
 	u64 addr, match;
@@ -610,7 +609,10 @@ static bool ufshcd_mcq_sqe_search(struct ufs_hba *hba,
 			ret = true;
 			goto out;
 		}
-		sq_head_slot = (sq_head_slot + 1) & mask;
+
+		sq_head_slot++;
+		if (sq_head_slot == hwq->max_entries)
+			sq_head_slot = 0;
 	}
 
 out:
-- 
2.7.4