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Message-ID: <20231227061837.GH2814@thinkpad> Date: Wed, 27 Dec 2023 11:48:37 +0530 From: Manivannan Sadhasivam <mani@...nel.org> To: Andrew Halaney <ahalaney@...hat.com> Cc: Andy Gross <agross@...nel.org>, Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, Manivannan Sadhasivam <mani@...nel.org>, "James E.J. Bottomley" <jejb@...ux.ibm.com>, "Martin K. Petersen" <martin.petersen@...cle.com>, Hannes Reinecke <hare@...e.de>, Janek Kotas <jank@...ence.com>, Alim Akhtar <alim.akhtar@...sung.com>, Avri Altman <avri.altman@....com>, Bart Van Assche <bvanassche@....org>, Can Guo <quic_cang@...cinc.com>, Will Deacon <will@...nel.org>, linux-arm-msm@...r.kernel.org, linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH RFC v3 10/11] scsi: ufs: core: Perform read back to commit doorbell On Thu, Dec 21, 2023 at 01:09:56PM -0600, Andrew Halaney wrote: > Currently, the doorbell is written to and a wmb() is used to commit it > immediately. > > wmb() ensures that the write completes before following writes occur, > 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 wmb()'s > purpose wasn't to add extra ordering (on top of the ordering guaranteed > by writel()/readl()), it can safely be removed. > > Fixes: ad1a1b9cd67a ("scsi: ufs: commit descriptors before setting the doorbell") > Signed-off-by: Andrew Halaney <ahalaney@...hat.com> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org> - Mani > --- > drivers/ufs/core/ufshcd.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c > index 75a03ee9a1ba..caebd589e08c 100644 > --- a/drivers/ufs/core/ufshcd.c > +++ b/drivers/ufs/core/ufshcd.c > @@ -7050,7 +7050,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba, > > ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL); > /* Make sure that doorbell is committed immediately */ > - wmb(); > + ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL); > > spin_unlock_irqrestore(host->host_lock, flags); > > > -- > 2.43.0 > -- மணிவண்ணன் சதாசிவம்
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