| Message ID | 20231221-ufs-reset-ensure-effect-before-delay-v3-10-2195a1b66d2e@redhat.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | scsi: ufs: Remove overzealous memory barriers | expand |
On 12/21/23 11:09, Andrew Halaney wrote: > diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c > index 75a03ee9a1ba..caebd589e08c 100644 > --- a/drivers/ufs/core/ufshcd.c > +++ b/drivers/ufs/core/ufshcd.c > @@ -7050,7 +7050,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba, > > ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL); > /* Make sure that doorbell is committed immediately */ > - wmb(); > + ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL); > > spin_unlock_irqrestore(host->host_lock, flags); There is a wait_for_completion_io_timeout() call later in this function and it is safe to write to the REG_UTP_TASK_REQ_DOOR_BELL register from multiple threads concurrently so I think the above wmb() call can be left out entirely. Thanks, Bart.
On 12/22/2023 3:09 AM, Andrew Halaney wrote: > Currently, the doorbell is written to and a wmb() is used to commit it > immediately. > > wmb() ensures that the write completes before following writes occur, > 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 wmb()'s > purpose wasn't to add extra ordering (on top of the ordering guaranteed > by writel()/readl()), it can safely be removed. > > Fixes: ad1a1b9cd67a ("scsi: ufs: commit descriptors before setting the doorbell") > Signed-off-by: Andrew Halaney <ahalaney@redhat.com> > --- > drivers/ufs/core/ufshcd.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c > index 75a03ee9a1ba..caebd589e08c 100644 > --- a/drivers/ufs/core/ufshcd.c > +++ b/drivers/ufs/core/ufshcd.c > @@ -7050,7 +7050,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba, > > ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL); > /* Make sure that doorbell is committed immediately */ > - wmb(); > + ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL); > > spin_unlock_irqrestore(host->host_lock, flags); > > Reviewed-by: Can Guo <quic_cang@quicinc.com>
On Thu, Dec 21, 2023 at 01:09:56PM -0600, Andrew Halaney wrote: > Currently, the doorbell is written to and a wmb() is used to commit it > immediately. > > wmb() ensures that the write completes before following writes occur, > 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 wmb()'s > purpose wasn't to add extra ordering (on top of the ordering guaranteed > by writel()/readl()), it can safely be removed. > > Fixes: ad1a1b9cd67a ("scsi: ufs: commit descriptors before setting the doorbell") > Signed-off-by: Andrew Halaney <ahalaney@redhat.com> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> - Mani > --- > drivers/ufs/core/ufshcd.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c > index 75a03ee9a1ba..caebd589e08c 100644 > --- a/drivers/ufs/core/ufshcd.c > +++ b/drivers/ufs/core/ufshcd.c > @@ -7050,7 +7050,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba, > > ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL); > /* Make sure that doorbell is committed immediately */ > - wmb(); > + ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL); > > spin_unlock_irqrestore(host->host_lock, flags); > > > -- > 2.43.0 >
diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c index 75a03ee9a1ba..caebd589e08c 100644 --- a/drivers/ufs/core/ufshcd.c +++ b/drivers/ufs/core/ufshcd.c @@ -7050,7 +7050,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba, ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL); /* Make sure that doorbell is committed immediately */ - wmb(); + ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL); spin_unlock_irqrestore(host->host_lock, flags);
Currently, the doorbell is written to and a wmb() is used to commit it immediately. wmb() ensures that the write completes before following writes occur, 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 wmb()'s purpose wasn't to add extra ordering (on top of the ordering guaranteed by writel()/readl()), it can safely be removed. Fixes: ad1a1b9cd67a ("scsi: ufs: commit descriptors before setting the doorbell") Signed-off-by: Andrew Halaney <ahalaney@redhat.com> --- drivers/ufs/core/ufshcd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)