On Sat 23 Apr 07:02 PDT 2022, Manivannan Sadhasivam wrote: > The wmb() inside ufshcd_send_command() is added to make sure that the > doorbell is committed immediately. This leads to couple of expectations: > > 1. The doorbell write should complete before the function return. > 2. The doorbell write should not cross the function boundary. > > 2nd expectation is fullfilled by the Linux memory model as there is a > guarantee that the critical section won't cross the unlock (release) > operation. > > 1st expectation is not really needed here as there is no following read/ > write that depends on the doorbell to be complete implicitly. Even if the > doorbell write is in a CPUs Write Buffer (WB), wmb() won't flush it. And > there is no real need of a WB flush here as well. > > So let's get rid of the wmb() that seems redundant. > > Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx> Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx> Regards, Bjorn > --- > drivers/scsi/ufs/ufshcd.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c > index 9349557b8a01..ec514a6c5393 100644 > --- a/drivers/scsi/ufs/ufshcd.c > +++ b/drivers/scsi/ufs/ufshcd.c > @@ -2116,9 +2116,6 @@ void ufshcd_send_command(struct ufs_hba *hba, unsigned int task_tag) > __set_bit(task_tag, &hba->outstanding_reqs); > ufshcd_writel(hba, 1 << task_tag, REG_UTP_TRANSFER_REQ_DOOR_BELL); > spin_unlock_irqrestore(&hba->outstanding_lock, flags); > - > - /* Make sure that doorbell is committed immediately */ > - wmb(); > } > > /** > -- > 2.25.1 >
