| Message ID | 20231221-ufs-reset-ensure-effect-before-delay-v2-3-75af2a9bae51@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | scsi: ufs: Remove overzealous memory barriers | expand |
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@redhat.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 >
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); } 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; }
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@redhat.com> --- drivers/ufs/host/ufs-qcom.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)