linux-kernel - [PATCH] scsi: mpt3sas: remove redundant wmb on arm/arm64

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Date:   Fri,  7 Apr 2017 12:41:45 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-scsi@...r.kernel.org, timur@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>,
        Sathya Prakash <sathya.prakash@...adcom.com>,
        Chaitra P B <chaitra.basappa@...adcom.com>,
        Suganath Prabu Subramani 
        <suganath-prabu.subramani@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        MPT-FusionLinux.pdl@...adcom.com (open list:LSILOGIC MPT FUSION DRIVERS
        (FC/SAS/SPI)), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] scsi: mpt3sas: remove redundant wmb on arm/arm64

Due to relaxed ordering requirements on multiple architectures,
drivers are required to use wmb/rmb/mb combinations when they
need to guarantee observability between the memory and the HW.

The mpt3sas driver is already using wmb() for this purpose.
However, it issues a writel following wmb(). writel() function
on arm/arm64 arhictectures have an embedded wmb() call inside.

This results in unnecessary performance loss and code duplication.

The kernel has been updated to support relaxed read/write
API to be supported across all architectures now.

The right thing was to either call __raw_writel/__raw_readl or
write_relaxed/read_relaxed for multi-arch compatibility.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/scsi/mpt3sas/mpt3sas_base.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/scsi/mpt3sas/mpt3sas_base.c b/drivers/scsi/mpt3sas/mpt3sas_base.c
index 5b7aec5..6e42036 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_base.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_base.c
@@ -1026,8 +1026,8 @@ static int mpt3sas_remove_dead_ioc_func(void *arg)
 				ioc->reply_free[ioc->reply_free_host_index] =
 				    cpu_to_le32(reply);
 				wmb();
-				writel(ioc->reply_free_host_index,
-				    &ioc->chip->ReplyFreeHostIndex);
+				writel_relaxed(ioc->reply_free_host_index,
+					       &ioc->chip->ReplyFreeHostIndex);
 			}
 		}
 
@@ -1076,8 +1076,8 @@ static int mpt3sas_remove_dead_ioc_func(void *arg)
 
 	wmb();
 	if (ioc->is_warpdrive) {
-		writel(reply_q->reply_post_host_index,
-		ioc->reply_post_host_index[msix_index]);
+		writel_relaxed(reply_q->reply_post_host_index,
+			       ioc->reply_post_host_index[msix_index]);
 		atomic_dec(&reply_q->busy);
 		return IRQ_HANDLED;
 	}
@@ -1098,13 +1098,14 @@ static int mpt3sas_remove_dead_ioc_func(void *arg)
 	 * value in MSIxIndex field.
 	 */
 	if (ioc->combined_reply_queue)
-		writel(reply_q->reply_post_host_index | ((msix_index  & 7) <<
-			MPI2_RPHI_MSIX_INDEX_SHIFT),
-			ioc->replyPostRegisterIndex[msix_index/8]);
+		writel_relaxed(reply_q->reply_post_host_index |
+			       ((msix_index  & 7) <<
+			       MPI2_RPHI_MSIX_INDEX_SHIFT),
+			       ioc->replyPostRegisterIndex[msix_index/8]);
 	else
-		writel(reply_q->reply_post_host_index | (msix_index <<
-			MPI2_RPHI_MSIX_INDEX_SHIFT),
-			&ioc->chip->ReplyPostHostIndex);
+		writel_relaxed(reply_q->reply_post_host_index |
+			       (msix_index << MPI2_RPHI_MSIX_INDEX_SHIFT),
+			       &ioc->chip->ReplyPostHostIndex);
 	atomic_dec(&reply_q->busy);
 	return IRQ_HANDLED;
 }
-- 
1.9.1