| Message ID | 20240329-ufs-reset-ensure-effect-before-delay-v5-4-181252004586@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | scsi: ufs: Remove overzealous memory barriers | expand |
On Fri, Mar 29, 2024 at 03:46:46PM -0500, Andrew Halaney wrote: > Currently, the QUNIPRO_SEL bit is written to and then an mb() is used to > ensure that completes before continuing. > > 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 > > But, there's really no reason to even ensure completion before > continuing. The only requirement here is that this write is ordered to > this endpoint (which readl()/writel() guarantees already). For that > reason the mb() can be dropped altogether without anything forcing > completion. > > Fixes: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations") > Signed-off-by: Andrew Halaney <ahalaney@redhat.com> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> - Mani > --- > drivers/ufs/host/ufs-qcom.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c > index 649fada24345..66a6c95f5d72 100644 > --- a/drivers/ufs/host/ufs-qcom.c > +++ b/drivers/ufs/host/ufs-qcom.c > @@ -278,9 +278,6 @@ static void ufs_qcom_select_unipro_mode(struct ufs_qcom_host *host) > > if (host->hw_ver.major >= 0x05) > ufshcd_rmwl(host->hba, QUNIPRO_G4_SEL, 0, REG_UFS_CFG0); > - > - /* make sure above configuration is applied before we return */ > - mb(); > } > > /* > > -- > 2.44.0 > >
diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c index 649fada24345..66a6c95f5d72 100644 --- a/drivers/ufs/host/ufs-qcom.c +++ b/drivers/ufs/host/ufs-qcom.c @@ -278,9 +278,6 @@ static void ufs_qcom_select_unipro_mode(struct ufs_qcom_host *host) if (host->hw_ver.major >= 0x05) ufshcd_rmwl(host->hba, QUNIPRO_G4_SEL, 0, REG_UFS_CFG0); - - /* make sure above configuration is applied before we return */ - mb(); } /*
Currently, the QUNIPRO_SEL bit is written to and then an mb() is used to ensure that completes before continuing. 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 But, there's really no reason to even ensure completion before continuing. The only requirement here is that this write is ordered to this endpoint (which readl()/writel() guarantees already). For that reason the mb() can be dropped altogether without anything forcing completion. Fixes: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations") Signed-off-by: Andrew Halaney <ahalaney@redhat.com> --- drivers/ufs/host/ufs-qcom.c | 3 --- 1 file changed, 3 deletions(-)