On Fri, Mar 29, 2024 at 03:46:52PM -0500, 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 > > But, completion and taking effect aren't necessary to guarantee here. > > There's already other examples of the doorbell being rung that don't do > this. The writel() of the doorbell guarantees prior writes by this > thread (to the request being setup for example) complete prior to the > ringing of the doorbell, and the following > wait_for_completion_io_timeout() doesn't require any special memory > barriers either. > > With that in mind, just remove the wmb() altogether here. > > Fixes: ad1a1b9cd67a ("scsi: ufs: commit descriptors before setting the doorbell") > Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> - Mani > --- > drivers/ufs/core/ufshcd.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c > index dfa4f827766a..a2f2941450fd 100644 > --- a/drivers/ufs/core/ufshcd.c > +++ b/drivers/ufs/core/ufshcd.c > @@ -7090,10 +7090,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba, > > /* send command to the controller */ > __set_bit(task_tag, &hba->outstanding_tasks); > - > ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL); > - /* Make sure that doorbell is committed immediately */ > - wmb(); > > spin_unlock_irqrestore(host->host_lock, flags); > > > -- > 2.44.0 > > -- மணிவண்ணன் சதாசிவம்
