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Message-ID: <20231227054734.GA2814@thinkpad> Date: Wed, 27 Dec 2023 11:17:34 +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>, 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 03/11] scsi: ufs: qcom: Perform read back after writing testbus config On Thu, Dec 21, 2023 at 12:25:20PM -0600, Andrew Halaney wrote: > 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 > > Let's do that to ensure the bit hits 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: 9c46b8676271 ("scsi: ufs-qcom: dump additional testbus registers") > Signed-off-by: Andrew Halaney <ahalaney@...hat.com> > --- > drivers/ufs/host/ufs-qcom.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c > index 4c15c8a1d058..6df2ab3b6f23 100644 > --- a/drivers/ufs/host/ufs-qcom.c > +++ b/drivers/ufs/host/ufs-qcom.c > @@ -1332,6 +1332,9 @@ static void ufs_qcom_enable_test_bus(struct ufs_qcom_host *host) > ufshcd_rmwl(host->hba, UFS_REG_TEST_BUS_EN, > UFS_REG_TEST_BUS_EN, REG_UFS_CFG1); > ufshcd_rmwl(host->hba, TEST_BUS_EN, TEST_BUS_EN, REG_UFS_CFG1); > + > + /* dummy read to ensure this has been enabled prior to returning */ > + ufshcd_readl(host->hba, REG_UFS_CFG1); In this case, I do not see the necessity to do a read back itself since there is no delay afterwards nor any dependent operation in an altogether different domain. So removing the mb() should be sufficient. - Mani > } > > static void ufs_qcom_get_default_testbus_cfg(struct ufs_qcom_host *host) > @@ -1429,11 +1432,6 @@ 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; > } > > -- > 2.43.0 > -- மணிவண்ணன் சதாசிவம்
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