| Message ID | 20231221-ufs-reset-ensure-effect-before-delay-v2-6-75af2a9bae51@redhat.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | scsi: ufs: Remove overzealous memory barriers | expand |
On Thu, Dec 21, 2023 at 12:25:23PM -0600, Andrew Halaney wrote: > Currently, HCLKDIV is 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 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: d90996dae8e4 ("scsi: ufs: Add UFS platform driver for Cadence UFS") > Signed-off-by: Andrew Halaney <ahalaney@redhat.com> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> - Mani > --- > drivers/ufs/host/cdns-pltfrm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/ufs/host/cdns-pltfrm.c b/drivers/ufs/host/cdns-pltfrm.c > index bb30267da471..66811d8d1929 100644 > --- a/drivers/ufs/host/cdns-pltfrm.c > +++ b/drivers/ufs/host/cdns-pltfrm.c > @@ -136,7 +136,7 @@ static int cdns_ufs_set_hclkdiv(struct ufs_hba *hba) > * Make sure the register was updated, > * UniPro layer will not work with an incorrect value. > */ > - mb(); > + ufshcd_readl(hba, CDNS_UFS_REG_HCLKDIV); > > return 0; > } > > -- > 2.43.0 >
diff --git a/drivers/ufs/host/cdns-pltfrm.c b/drivers/ufs/host/cdns-pltfrm.c index bb30267da471..66811d8d1929 100644 --- a/drivers/ufs/host/cdns-pltfrm.c +++ b/drivers/ufs/host/cdns-pltfrm.c @@ -136,7 +136,7 @@ static int cdns_ufs_set_hclkdiv(struct ufs_hba *hba) * Make sure the register was updated, * UniPro layer will not work with an incorrect value. */ - mb(); + ufshcd_readl(hba, CDNS_UFS_REG_HCLKDIV); return 0; }
Currently, HCLKDIV is 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 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: d90996dae8e4 ("scsi: ufs: Add UFS platform driver for Cadence UFS") Signed-off-by: Andrew Halaney <ahalaney@redhat.com> --- drivers/ufs/host/cdns-pltfrm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)