| Message ID | 20231221-ufs-reset-ensure-effect-before-delay-v3-1-2195a1b66d2e@redhat.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | scsi: ufs: Remove overzealous memory barriers | expand |
On 12/22/2023 3:09 AM, Andrew Halaney wrote: > Currently, the reset bit for the UFS provided reset controller (used by > its phy) is written to, and then a mb() happens to try and ensure that > hit the device. Immediately afterwards a usleep_range() occurs. > > 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. By doing so and > guaranteeing the ordering against the immediately following > usleep_range(), the mb() can safely be removed. > > Fixes: 81c0fc51b7a7 ("ufs-qcom: add support for Qualcomm Technologies Inc platforms") > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > Signed-off-by: Andrew Halaney <ahalaney@redhat.com> > --- > drivers/ufs/host/ufs-qcom.h | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/drivers/ufs/host/ufs-qcom.h b/drivers/ufs/host/ufs-qcom.h > index 9dd9a391ebb7..b9de170983c9 100644 > --- a/drivers/ufs/host/ufs-qcom.h > +++ b/drivers/ufs/host/ufs-qcom.h > @@ -151,10 +151,10 @@ static inline void ufs_qcom_assert_reset(struct ufs_hba *hba) > ufshcd_rmwl(hba, UFS_PHY_SOFT_RESET, UFS_PHY_SOFT_RESET, REG_UFS_CFG1); > > /* > - * Make sure assertion of ufs phy reset is written to > - * register before returning > + * Dummy read to ensure the write takes effect before doing any sort > + * of delay > */ > - mb(); > + ufshcd_readl(hba, REG_UFS_CFG1); > } > > static inline void ufs_qcom_deassert_reset(struct ufs_hba *hba) > @@ -162,10 +162,10 @@ static inline void ufs_qcom_deassert_reset(struct ufs_hba *hba) > ufshcd_rmwl(hba, UFS_PHY_SOFT_RESET, 0, REG_UFS_CFG1); > > /* > - * Make sure de-assertion of ufs phy reset is written to > - * register before returning > + * Dummy read to ensure the write takes effect before doing any sort > + * of delay > */ > - mb(); > + ufshcd_readl(hba, REG_UFS_CFG1); > } > > /* Host controller hardware version: major.minor.step */ > Reviewed-by: Can Guo <quic_cang@quicinc.com>
diff --git a/drivers/ufs/host/ufs-qcom.h b/drivers/ufs/host/ufs-qcom.h index 9dd9a391ebb7..b9de170983c9 100644 --- a/drivers/ufs/host/ufs-qcom.h +++ b/drivers/ufs/host/ufs-qcom.h @@ -151,10 +151,10 @@ static inline void ufs_qcom_assert_reset(struct ufs_hba *hba) ufshcd_rmwl(hba, UFS_PHY_SOFT_RESET, UFS_PHY_SOFT_RESET, REG_UFS_CFG1); /* - * Make sure assertion of ufs phy reset is written to - * register before returning + * Dummy read to ensure the write takes effect before doing any sort + * of delay */ - mb(); + ufshcd_readl(hba, REG_UFS_CFG1); } static inline void ufs_qcom_deassert_reset(struct ufs_hba *hba) @@ -162,10 +162,10 @@ static inline void ufs_qcom_deassert_reset(struct ufs_hba *hba) ufshcd_rmwl(hba, UFS_PHY_SOFT_RESET, 0, REG_UFS_CFG1); /* - * Make sure de-assertion of ufs phy reset is written to - * register before returning + * Dummy read to ensure the write takes effect before doing any sort + * of delay */ - mb(); + ufshcd_readl(hba, REG_UFS_CFG1); } /* Host controller hardware version: major.minor.step */
Currently, the reset bit for the UFS provided reset controller (used by its phy) is written to, and then a mb() happens to try and ensure that hit the device. Immediately afterwards a usleep_range() occurs. 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. By doing so and guaranteeing the ordering against the immediately following usleep_range(), the mb() can safely be removed. Fixes: 81c0fc51b7a7 ("ufs-qcom: add support for Qualcomm Technologies Inc platforms") Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> Signed-off-by: Andrew Halaney <ahalaney@redhat.com> --- drivers/ufs/host/ufs-qcom.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)