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Mon, 22 Jan 2024 09:21:41 -0800 (PST) X-Received: by 2002:a05:6358:9386:b0:173:203:c5c1 with SMTP id h6-20020a056358938600b001730203c5c1mr2261899rwb.62.1705944101357; Mon, 22 Jan 2024 09:21:41 -0800 (PST) Received: from [192.168.1.163] ([2600:1700:1ff0:d0e0::37]) by smtp.gmail.com with ESMTPSA id lf3-20020a0562142cc300b00680c25f5f06sm2567738qvb.86.2024.01.22.09.21.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jan 2024 09:21:37 -0800 (PST) From: Andrew Halaney Date: Mon, 22 Jan 2024 11:21:28 -0600 Subject: [PATCH RFC v4 03/11] scsi: ufs: qcom: Remove unnecessary mb() after writing testbus config Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240122-ufs-reset-ensure-effect-before-delay-v4-3-6c48432151cc@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 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1788815063052488605 X-GMAIL-MSGID: 1788815063052488605 Currently, the testbus configuration is written and completed with an mb(). 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 But, there's really no reason to even ensure completion before continuing. The only requirement here is that this write is ordered to this endpoint (which readl()/writel() guarantees already). For that reason the mb() can be dropped altogether without anything forcing completion. Fixes: 9c46b8676271 ("scsi: ufs-qcom: dump additional testbus registers") Signed-off-by: Andrew Halaney --- drivers/ufs/host/ufs-qcom.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c index 0603a07a23a2..a489c8c6f849 100644 --- a/drivers/ufs/host/ufs-qcom.c +++ b/drivers/ufs/host/ufs-qcom.c @@ -1429,11 +1429,6 @@ int ufs_qcom_testbus_config(struct ufs_qcom_host *host) (u32)host->testbus.select_minor << offset, reg); ufs_qcom_enable_test_bus(host); - /* - * Make sure the test bus configuration is - * committed before returning. - */ - mb(); return 0; }