| Message ID | 20240329-ufs-reset-ensure-effect-before-delay-v5-3-181252004586@redhat.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | scsi: ufs: Remove overzealous memory barriers | expand |
On Fri, Mar 29, 2024 at 03:46:45PM -0500, 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 > > 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: 9c46b8676271 ("scsi: ufs-qcom: dump additional testbus registers") > Signed-off-by: Andrew Halaney <ahalaney@redhat.com> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> - Mani > --- > drivers/ufs/host/ufs-qcom.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c > index 804dc8153e7b..649fada24345 100644 > --- a/drivers/ufs/host/ufs-qcom.c > +++ b/drivers/ufs/host/ufs-qcom.c > @@ -1445,11 +1445,6 @@ 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; > } > > -- > 2.44.0 > >
diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c index 804dc8153e7b..649fada24345 100644 --- a/drivers/ufs/host/ufs-qcom.c +++ b/drivers/ufs/host/ufs-qcom.c @@ -1445,11 +1445,6 @@ 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; }
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 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: 9c46b8676271 ("scsi: ufs-qcom: dump additional testbus registers") Signed-off-by: Andrew Halaney <ahalaney@redhat.com> --- drivers/ufs/host/ufs-qcom.c | 5 ----- 1 file changed, 5 deletions(-)