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Message-ID: <20231227061643.GG2814@thinkpad> Date: Wed, 27 Dec 2023 11:46:43 +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>, "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 09/11] scsi: ufs: core: Perform read back after disabling UIC_COMMAND_COMPL On Thu, Dec 21, 2023 at 01:09:55PM -0600, Andrew Halaney wrote: > Currently, the UIC_COMMAND_COMPL interrupt is disabled and a wmb() is > used to complete the register write before any following writes. > > wmb() ensures the writes complete in that order, 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: d75f7fe495cf ("scsi: ufs: reduce the interrupts for power mode change requests") > 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 bb603769b029..75a03ee9a1ba 100644 > --- a/drivers/ufs/core/ufshcd.c > +++ b/drivers/ufs/core/ufshcd.c > @@ -4240,7 +4240,7 @@ static int ufshcd_uic_pwr_ctrl(struct ufs_hba *hba, struct uic_command *cmd) > * Make sure UIC command completion interrupt is disabled before > * issuing UIC command. > */ > - wmb(); > + ufshcd_readl(hba, REG_INTERRUPT_ENABLE); > reenable_intr = true; > } > spin_unlock_irqrestore(hba->host->host_lock, flags); > > -- > 2.43.0 > -- மணிவண்ணன் சதாசிவம்
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