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Bottomley" , "Martin K. Petersen" , Hannes Reinecke , Janek Kotas , Alim Akhtar , Avri Altman , Bart Van Assche , Can Guo Cc: Andrew Halaney , Will Deacon , linux-arm-msm@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH RFC v4 10/11] scsi: ufs: core: Remove unnecessary wmb() after ringing doorbell Date: Mon, 22 Jan 2024 11:24:06 -0600 Message-ID: <20240122-ufs-reset-ensure-effect-before-delay-v4-10-90a54c832508@redhat.com> X-Mailer: git-send-email 2.43.0 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> Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" X-Mailer: b4 0.12.3 Content-Transfer-Encoding: quoted-printable Currently, the doorbell is written to and a wmb() is used to commit it=0D immediately.=0D =0D wmb() ensures that the write completes before following writes occur,=0D but completion doesn't mean that it isn't stored in a buffer somewhere.=0D The recommendation for ensuring this bit has taken effect on the device=0D is to perform a read back to force it to make it all the way to the=0D device. This is documented in device-io.rst and a talk by Will Deacon on=0D this can be seen over here:=0D =0D https://youtu.be/i6DayghhA8Q?si=3DMiyxB5cKJXSaoc01&t=3D1678=0D =0D But, completion and taking effect aren't necessary to guarantee here.=0D =0D There's already other examples of the doorbell being rung that don't do=0D this. The writel() of the doorbell guarantees prior writes by this=0D thread (to the request being setup for example) complete prior to the=0D ringing of the doorbell, and the following=0D wait_for_completion_io_timeout() doesn't require any special memory=0D barriers either.=0D =0D With that in mind, just remove the wmb() altogether here.=0D =0D Fixes: ad1a1b9cd67a ("scsi: ufs: commit descriptors before setting the door= bell")=0D Signed-off-by: Andrew Halaney =0D ---=0D drivers/ufs/core/ufshcd.c | 3 ---=0D 1 file changed, 3 deletions(-)=0D =0D diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c=0D index 9bf490bb8eed..21f93d8e5818 100644=0D --- a/drivers/ufs/core/ufshcd.c=0D +++ b/drivers/ufs/core/ufshcd.c=0D @@ -7047,10 +7047,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba= ,=0D =0D /* send command to the controller */=0D __set_bit(task_tag, &hba->outstanding_tasks);=0D -=0D ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL);=0D - /* Make sure that doorbell is committed immediately */=0D - wmb();=0D =0D spin_unlock_irqrestore(host->host_lock, flags);=0D =0D =0D -- =0D 2.43.0=0D =0D