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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
Subject: [PATCH v5 02/11] scsi: ufs: qcom: Perform read back after writing
 REG_UFS_SYS1CLK_1US
Date: Fri, 29 Mar 2024 15:46:44 -0500
Message-ID: <20240329-ufs-reset-ensure-effect-before-delay-v5-2-181252004586@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 after writing to REG_UFS_SYS1CLK_1US a mb() is used to ensure=0D
that write has gone through to the device.=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 this bit has 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 bit hits 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: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and powe=
r optimizations")=0D
Reviewed-by: Can Guo <quic_cang@quicinc.com>=0D
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>=0D
---=0D
 drivers/ufs/host/ufs-qcom.c | 2 +-=0D
 1 file changed, 1 insertion(+), 1 deletion(-)=0D
=0D
diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c=0D
index 06859e17b67b..804dc8153e7b 100644=0D
--- a/drivers/ufs/host/ufs-qcom.c=0D
+++ b/drivers/ufs/host/ufs-qcom.c=0D
@@ -501,7 +501,7 @@ static int ufs_qcom_cfg_timers(struct ufs_hba *hba, u32=
 gear,=0D
 		 * make sure above write gets applied before we return from=0D
 		 * this function.=0D
 		 */=0D
-		mb();=0D
+		ufshcd_readl(hba, REG_UFS_SYS1CLK_1US);=0D
 	}=0D
 =0D
 	return 0;=0D
=0D
-- =0D
2.44.0=0D
=0D