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Mon, 22 Jan 2024 09:21:36 -0800 (PST) X-Google-Smtp-Source: AGHT+IGXXHmtJA2fouZvXWZRPuBxW0a4kvTjX4BO9HFSw11OKwZJkbRHiV8Pi9144jdwfGRsA2ozXw== X-Received: by 2002:a05:6214:1d2e:b0:684:d2a1:990f with SMTP id f14-20020a0562141d2e00b00684d2a1990fmr6930834qvd.40.1705944096647; Mon, 22 Jan 2024 09:21:36 -0800 (PST) Received: from [192.168.1.163] ([2600:1700:1ff0:d0e0::37]) by smtp.gmail.com with ESMTPSA id lf3-20020a0562142cc300b00680c25f5f06sm2567738qvb.86.2024.01.22.09.21.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jan 2024 09:21:33 -0800 (PST) From: Andrew Halaney Date: Mon, 22 Jan 2024 11:21:27 -0600 Subject: [PATCH RFC v4 02/11] scsi: ufs: qcom: Perform read back after writing REG_UFS_SYS1CLK_1US Precedence: bulk X-Mailing-List: linux-scsi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240122-ufs-reset-ensure-effect-before-delay-v4-2-6c48432151cc@redhat.com> References: <20240122-ufs-reset-ensure-effect-before-delay-v4-0-6c48432151cc@redhat.com> In-Reply-To: <20240122-ufs-reset-ensure-effect-before-delay-v4-0-6c48432151cc@redhat.com> To: Andy Gross , Bjorn Andersson , Konrad Dybcio , Manivannan Sadhasivam , "James E.J. Bottomley" , "Martin K. Petersen" , Hannes Reinecke , Janek Kotas , Alim Akhtar , Avri Altman , Bart Van Assche , Can Guo Cc: Will Deacon , linux-arm-msm@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Halaney X-Mailer: b4 0.12.3 Currently after writing to REG_UFS_SYS1CLK_1US a mb() is used to ensure that write has gone through to the device. mb() ensure that the write completes, but completion doesn't mean that it isn't stored in a buffer somewhere. The recommendation for ensuring this bit has taken effect on the device is to perform a read back to force it to make it all the way to the device. This is documented in device-io.rst and a talk by Will Deacon on this can be seen over here: https://youtu.be/i6DayghhA8Q?si=MiyxB5cKJXSaoc01&t=1678 Let's do that to ensure the bit hits the device. Because the mb()'s purpose wasn't to add extra ordering (on top of the ordering guaranteed by writel()/readl()), it can safely be removed. Fixes: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations") Reviewed-by: Can Guo Signed-off-by: Andrew Halaney --- drivers/ufs/host/ufs-qcom.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c index 39eef470f8fa..0603a07a23a2 100644 --- a/drivers/ufs/host/ufs-qcom.c +++ b/drivers/ufs/host/ufs-qcom.c @@ -501,7 +501,7 @@ static int ufs_qcom_cfg_timers(struct ufs_hba *hba, u32 gear, * make sure above write gets applied before we return from * this function. */ - mb(); + ufshcd_readl(hba, REG_UFS_SYS1CLK_1US); } return 0;