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* [PATCH V2] scsi: mpt3sas: remove redundant wmb
@ 2017-04-07 19:06 Sinan Kaya
  2017-04-20  2:28 ` Martin K. Petersen
  2017-04-24 22:32 ` Martin K. Petersen
  0 siblings, 2 replies; 6+ messages in thread
From: Sinan Kaya @ 2017-04-07 19:06 UTC (permalink / raw)
  To: linux-scsi, timur
  Cc: linux-arm-msm, linux-arm-kernel, Sinan Kaya, Sathya Prakash,
	Chaitra P B, Suganath Prabu Subramani, James E.J. Bottomley,
	Martin K. Petersen,
	open list:LSILOGIC MPT FUSION DRIVERS (FC/SAS/SPI),
	open list

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.

writel already guarantees ordering for both cpu and bus. we don't need
additional wmb()

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
---
 drivers/scsi/mpt3sas/mpt3sas_base.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/scsi/mpt3sas/mpt3sas_base.c b/drivers/scsi/mpt3sas/mpt3sas_base.c
index 5b7aec5..18039bb 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_base.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_base.c
@@ -1025,7 +1025,6 @@ static int mpt3sas_remove_dead_ioc_func(void *arg)
 				    0 : ioc->reply_free_host_index + 1;
 				ioc->reply_free[ioc->reply_free_host_index] =
 				    cpu_to_le32(reply);
-				wmb();
 				writel(ioc->reply_free_host_index,
 				    &ioc->chip->ReplyFreeHostIndex);
 			}
@@ -1074,7 +1073,6 @@ static int mpt3sas_remove_dead_ioc_func(void *arg)
 		return IRQ_NONE;
 	}
 
-	wmb();
 	if (ioc->is_warpdrive) {
 		writel(reply_q->reply_post_host_index,
 		ioc->reply_post_host_index[msix_index]);
-- 
1.9.1

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2017-04-24 22:33 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-04-07 19:06 [PATCH V2] scsi: mpt3sas: remove redundant wmb Sinan Kaya
2017-04-20  2:28 ` Martin K. Petersen
2017-04-21  7:56   ` Sreekanth Reddy
2017-04-21 13:47     ` Sinan Kaya
2017-04-21 15:10     ` Brian King
2017-04-24 22:32 ` Martin K. Petersen

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