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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>
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 RFC v4 08/11] scsi: ufs: core: Perform read back after
 disabling interrupts
Date: Mon, 22 Jan 2024 11:24:04 -0600
Message-ID: <20240122-ufs-reset-ensure-effect-before-delay-v4-8-90a54c832508@redhat.com>
In-Reply-To: <20240122-ufs-reset-ensure-effect-before-delay-v4-0-90a54c832508@redhat.com>
References: <20240122-ufs-reset-ensure-effect-before-delay-v4-0-90a54c832508@redhat.com>
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Currently, interrupts are cleared and disabled prior to registering the=0D
interrupt. An mb() is used to complete the clear/disable writes before=0D
the interrupt is registered.=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 these 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: 199ef13cac7d ("scsi: ufs: avoid spurious UFS host controller interru=
pts")=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 e2e6002fe46a..9b6355555897 100644=0D
--- a/drivers/ufs/core/ufshcd.c=0D
+++ b/drivers/ufs/core/ufshcd.c=0D
@@ -10564,7 +10564,7 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *=
mmio_base, unsigned int irq)=0D
 	 * Make sure that UFS interrupts are disabled and any pending interrupt=0D
 	 * status is cleared before registering UFS interrupt handler.=0D
 	 */=0D
-	mb();=0D
+	ufshcd_readl(hba, REG_INTERRUPT_ENABLE);=0D
 =0D
 	/* IRQ registration */=0D
 	err =3D devm_request_irq(dev, irq, ufshcd_intr, IRQF_SHARED, UFSHCD, hba)=
;=0D
=0D
-- =0D
2.43.0=0D
=0D