| Message ID | 20231221-ufs-reset-ensure-effect-before-delay-v2-5-75af2a9bae51@redhat.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | scsi: ufs: Remove overzealous memory barriers | expand |
On Thu, Dec 21, 2023 at 12:25:22PM -0600, Andrew Halaney wrote: > Currently, the CGC enable bit is written 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 > > 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: 81c0fc51b7a7 ("ufs-qcom: add support for Qualcomm Technologies Inc platforms") > Signed-off-by: Andrew Halaney <ahalaney@redhat.com> For this patch, a read back would make sense since I'm not sure if the ICE block getting enabled afterwards is in the same domain or not. Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> - Mani > --- > drivers/ufs/host/ufs-qcom.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c > index ab1ff7432d11..3db19591d008 100644 > --- a/drivers/ufs/host/ufs-qcom.c > +++ b/drivers/ufs/host/ufs-qcom.c > @@ -409,7 +409,7 @@ static void ufs_qcom_enable_hw_clk_gating(struct ufs_hba *hba) > REG_UFS_CFG2); > > /* Ensure that HW clock gating is enabled before next operations */ > - mb(); > + ufshcd_readl(hba, REG_UFS_CFG2); > } > > static int ufs_qcom_hce_enable_notify(struct ufs_hba *hba, > > -- > 2.43.0 >
diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c index ab1ff7432d11..3db19591d008 100644 --- a/drivers/ufs/host/ufs-qcom.c +++ b/drivers/ufs/host/ufs-qcom.c @@ -409,7 +409,7 @@ static void ufs_qcom_enable_hw_clk_gating(struct ufs_hba *hba) REG_UFS_CFG2); /* Ensure that HW clock gating is enabled before next operations */ - mb(); + ufshcd_readl(hba, REG_UFS_CFG2); } static int ufs_qcom_hce_enable_notify(struct ufs_hba *hba,
Currently, the CGC enable bit is written 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 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: 81c0fc51b7a7 ("ufs-qcom: add support for Qualcomm Technologies Inc platforms") Signed-off-by: Andrew Halaney <ahalaney@redhat.com> --- drivers/ufs/host/ufs-qcom.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)