linux-kernel - [PATCH v4 5/7] scsi: ipr: Eliminate duplicate barriers on weakly-ordered archs

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Message-Id: <1521514207-10695-6-git-send-email-okaya@codeaurora.org>
Date:   Mon, 19 Mar 2018 22:50:05 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-scsi@...r.kernel.org, timur@...eaurora.org,
        sulrich@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>,
        Brian King <brking@...ibm.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 5/7] scsi: ipr: Eliminate duplicate barriers on weakly-ordered archs

Code includes barrier() followed by writel(). writel() already has a
barrier
on some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the
register write.

Since code already has an explicit barrier call, changing writeX() to
writeX_relaxed().

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/scsi/ipr.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
index e07dd99..209adac 100644
--- a/drivers/scsi/ipr.c
+++ b/drivers/scsi/ipr.c
@@ -762,9 +762,9 @@ static void ipr_mask_and_clear_interrupts(struct ipr_ioa_cfg *ioa_cfg,
 
 	/* Set interrupt mask to stop all new interrupts */
 	if (ioa_cfg->sis64)
-		writeq(~0, ioa_cfg->regs.set_interrupt_mask_reg);
+		writeq_relaxed(~0, ioa_cfg->regs.set_interrupt_mask_reg);
 	else
-		writel(~0, ioa_cfg->regs.set_interrupt_mask_reg);
+		writel_relaxed(~0, ioa_cfg->regs.set_interrupt_mask_reg);
 
 	/* Clear any pending interrupts */
 	if (ioa_cfg->sis64)
@@ -8435,7 +8435,8 @@ static int ipr_reset_enable_ioa(struct ipr_cmnd *ipr_cmd)
 	wmb();
 	if (ioa_cfg->sis64) {
 		/* Set the adapter to the correct endian mode. */
-		writel(IPR_ENDIAN_SWAP_KEY, ioa_cfg->regs.endian_swap_reg);
+		writel_relaxed(IPR_ENDIAN_SWAP_KEY,
+			       ioa_cfg->regs.endian_swap_reg);
 		int_reg = readl(ioa_cfg->regs.endian_swap_reg);
 	}
 
-- 
2.7.4