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Thu, 21 Dec 2023 10:17:52 -0800 (PST) X-Received: by 2002:a05:622a:94:b0:425:f0e0:eb6e with SMTP id o20-20020a05622a009400b00425f0e0eb6emr209477qtw.19.1703182671973; Thu, 21 Dec 2023 10:17:51 -0800 (PST) Received: from [192.168.1.163] ([2600:1700:1ff0:d0e0::37]) by smtp.gmail.com with ESMTPSA id hj10-20020a05622a620a00b00425e8c7d65fsm1025758qtb.23.2023.12.21.10.17.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Dec 2023 10:17:50 -0800 (PST) From: Andrew Halaney Date: Thu, 21 Dec 2023 12:16:47 -0600 Subject: [PATCH RFC v2 01/11] scsi: ufs: qcom: Perform read back after writing reset bit Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20231221-ufs-reset-ensure-effect-before-delay-v2-1-6dc6a48f2f19@redhat.com> References: <20231221-ufs-reset-ensure-effect-before-delay-v2-0-6dc6a48f2f19@redhat.com> In-Reply-To: <20231221-ufs-reset-ensure-effect-before-delay-v2-0-6dc6a48f2f19@redhat.com> To: Andy Gross , Bjorn Andersson , Konrad Dybcio , Manivannan Sadhasivam , "James E.J. Bottomley" , "Martin K. Petersen" , Yaniv Gardi , Dov Levenglick , Hannes Reinecke , Subhash Jadavani , Gilad Broner , Venkat Gopalakrishnan , Janek Kotas , Alim Akhtar , Avri Altman , Bart Van Assche , Anjana Hari , Dolev Raviv , Can Guo Cc: Will Deacon , linux-arm-msm@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Halaney , Manivannan Sadhasivam X-Mailer: b4 0.12.3 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1785916518042845666 X-GMAIL-MSGID: 1785916518042845666 Currently, the reset bit for the UFS provided reset controller (used by its phy) is written to, and then a mb() happens to try and ensure that hit the device. Immediately afterwards a usleep_range() occurs. 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. By doing so and guaranteeing the ordering against the immediately following usleep_range(), the mb() can safely be removed. Fixes: 81c0fc51b7a7 ("ufs-qcom: add support for Qualcomm Technologies Inc platforms") Reviewed-by: Manivannan Sadhasivam Signed-off-by: Andrew Halaney --- drivers/ufs/host/ufs-qcom.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/drivers/ufs/host/ufs-qcom.h b/drivers/ufs/host/ufs-qcom.h index 9dd9a391ebb7..b9de170983c9 100644 --- a/drivers/ufs/host/ufs-qcom.h +++ b/drivers/ufs/host/ufs-qcom.h @@ -151,10 +151,10 @@ static inline void ufs_qcom_assert_reset(struct ufs_hba *hba) ufshcd_rmwl(hba, UFS_PHY_SOFT_RESET, UFS_PHY_SOFT_RESET, REG_UFS_CFG1); /* - * Make sure assertion of ufs phy reset is written to - * register before returning + * Dummy read to ensure the write takes effect before doing any sort + * of delay */ - mb(); + ufshcd_readl(hba, REG_UFS_CFG1); } static inline void ufs_qcom_deassert_reset(struct ufs_hba *hba) @@ -162,10 +162,10 @@ static inline void ufs_qcom_deassert_reset(struct ufs_hba *hba) ufshcd_rmwl(hba, UFS_PHY_SOFT_RESET, 0, REG_UFS_CFG1); /* - * Make sure de-assertion of ufs phy reset is written to - * register before returning + * Dummy read to ensure the write takes effect before doing any sort + * of delay */ - mb(); + ufshcd_readl(hba, REG_UFS_CFG1); } /* Host controller hardware version: major.minor.step */