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Message-ID: <20231227061053.GE2814@thinkpad> Date: Wed, 27 Dec 2023 11:40:53 +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>, Yaniv Gardi <ygardi@...eaurora.org>, Dov Levenglick <dovl@...eaurora.org>, Hannes Reinecke <hare@...e.de>, Subhash Jadavani <subhashj@...eaurora.org>, Gilad Broner <gbroner@...eaurora.org>, Venkat Gopalakrishnan <venkatg@...eaurora.org>, Janek Kotas <jank@...ence.com>, Alim Akhtar <alim.akhtar@...sung.com>, Avri Altman <avri.altman@....com>, Bart Van Assche <bvanassche@....org>, Anjana Hari <quic_ahari@...cinc.com>, Dolev Raviv <draviv@...eaurora.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 v2 07/11] scsi: ufs: core: Perform read back after writing UTP_TASK_REQ_LIST_BASE_H On Thu, Dec 21, 2023 at 12:25:24PM -0600, Andrew Halaney wrote: > Currently, the UTP_TASK_REQ_LIST_BASE_L/UTP_TASK_REQ_LIST_BASE_H regs > are written to and then 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 these bits have 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 bits hit the device. Because the mb()'s > purpose wasn't to add extra ordering (on top of the ordering guaranteed > by writel()/readl()), it can safely be removed. > > Fixes: 88441a8d355d ("scsi: ufs: core: Add hibernation callbacks") > Signed-off-by: Andrew Halaney <ahalaney@...hat.com> This also I'm not sure whether we can safely remove readback. So, 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 d1e33328ff3f..7bfb556e5b8e 100644 > --- a/drivers/ufs/core/ufshcd.c > +++ b/drivers/ufs/core/ufshcd.c > @@ -10351,7 +10351,7 @@ int ufshcd_system_restore(struct device *dev) > * are updated with the latest queue addresses. Only after > * updating these addresses, we can queue the new commands. > */ > - mb(); > + ufshcd_readl(hba, REG_UTP_TASK_REQ_LIST_BASE_H); > > /* Resuming from hibernate, assume that link was OFF */ > ufshcd_set_link_off(hba); > > -- > 2.43.0 > -- மணிவண்ணன் சதாசிவம்
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