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From: Andrew Halaney <ahalaney@redhat.com>
To: Andy Gross <agross@kernel.org>,
	Bjorn Andersson <andersson@kernel.org>,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	Manivannan Sadhasivam <mani@kernel.org>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Hannes Reinecke <hare@suse.de>,
	Janek Kotas <jank@cadence.com>,
	Alim Akhtar <alim.akhtar@samsung.com>,
	Avri Altman <avri.altman@wdc.com>,
	Bart Van Assche <bvanassche@acm.org>,
	Can Guo <quic_cang@quicinc.com>,
	Anjana Hari <quic_ahari@quicinc.com>
Cc: Andrew Halaney <ahalaney@redhat.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-msm@vger.kernel.org,
	linux-scsi@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Subject: [PATCH v5 07/11] scsi: ufs: core: Perform read back after writing
 UTP_TASK_REQ_LIST_BASE_H
Date: Fri, 29 Mar 2024 15:46:49 -0500
Message-ID: <20240329-ufs-reset-ensure-effect-before-delay-v5-7-181252004586@redhat.com>
In-Reply-To: <20240329-ufs-reset-ensure-effect-before-delay-v5-0-181252004586@redhat.com>
References: <20240329-ufs-reset-ensure-effect-before-delay-v5-0-181252004586@redhat.com>
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Currently, the UTP_TASK_REQ_LIST_BASE_L/UTP_TASK_REQ_LIST_BASE_H regs=0D
are written to and then completed with an mb().=0D
=0D
mb() ensure that the write completes, but completion doesn't mean that=0D
it isn't stored in a buffer somewhere. The recommendation for=0D
ensuring these bits have taken effect on the device is to perform a read=0D
back to force it to make it all the way to the device. This is=0D
documented in device-io.rst and a talk by Will Deacon on this can=0D
be seen over here:=0D
=0D
    https://youtu.be/i6DayghhA8Q?si=3DMiyxB5cKJXSaoc01&t=3D1678=0D
=0D
Let's do that to ensure the bits hit the device. Because the mb()'s=0D
purpose wasn't to add extra ordering (on top of the ordering guaranteed=0D
by writel()/readl()), it can safely be removed.=0D
=0D
Fixes: 88441a8d355d ("scsi: ufs: core: Add hibernation callbacks")=0D
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>=0D
Reviewed-by: Bart Van Assche <bvanassche@acm.org>=0D
Reviewed-by: Can Guo <quic_cang@quicinc.com>=0D
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>=0D
---=0D
 drivers/ufs/core/ufshcd.c | 2 +-=0D
 1 file changed, 1 insertion(+), 1 deletion(-)=0D
=0D
diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c=0D
index e30fd125988d..a89887878d98 100644=0D
--- a/drivers/ufs/core/ufshcd.c=0D
+++ b/drivers/ufs/core/ufshcd.c=0D
@@ -10395,7 +10395,7 @@ int ufshcd_system_restore(struct device *dev)=0D
 	 * are updated with the latest queue addresses. Only after=0D
 	 * updating these addresses, we can queue the new commands.=0D
 	 */=0D
-	mb();=0D
+	ufshcd_readl(hba, REG_UTP_TASK_REQ_LIST_BASE_H);=0D
 =0D
 	/* Resuming from hibernate, assume that link was OFF */=0D
 	ufshcd_set_link_off(hba);=0D
=0D
-- =0D
2.44.0=0D
=0D