From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurence Oberman Subject: Re: [PATCH v4 1/7] scsi: hpsa: Eliminate duplicate barriers on weakly-ordered archs Date: Tue, 20 Mar 2018 12:51:58 -0400 Message-ID: <1521564718.13995.1.camel@redhat.com> References: <1521514207-10695-1-git-send-email-okaya@codeaurora.org> <1521514207-10695-2-git-send-email-okaya@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <1521514207-10695-2-git-send-email-okaya@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org To: Sinan Kaya , linux-scsi@vger.kernel.org, timur@codeaurora.org, sulrich@codeaurora.org Cc: linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Don Brace , "James E.J. Bottomley" , "Martin K. Petersen" , esc.storagedev@microsemi.com, linux-kernel@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org On Mon, 2018-03-19 at 22:50 -0400, Sinan Kaya wrote: > Code includes wmb() followed by writel(). writel() already has a > barrier on some architectures like arm64. > > This ends up CPU observing two barriers back to back before executing > the register write. > > Since code already has an explicit barrier call, changing writel() to > writel_relaxed(). > > Signed-off-by: Sinan Kaya > --- >  drivers/scsi/hpsa.h | 2 +- >  1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/scsi/hpsa.h b/drivers/scsi/hpsa.h > index 018f980..c7d7e6a 100644 > --- a/drivers/scsi/hpsa.h > +++ b/drivers/scsi/hpsa.h > @@ -599,7 +599,7 @@ static unsigned long > SA5_ioaccel_mode1_completed(struct ctlr_info *h, u8 q) >    * but with current driver design this is easiest. >    */ >   wmb(); > - writel((q << 24) | rq->current_entry, h->vaddr + > + writel_relaxed((q << 24) | rq->current_entry, h- > >vaddr + >   IOACCEL_MODE1_CONSUMER_INDEX); >   atomic_dec(&h->commands_outstanding); >   } This looks like it would work for the x86_64 and arm because of how its defined architecture specific for the x86_64 and the arm64 I guess its up to Don and the driver folks and if its worth the change. I am generally not a fan of messing with these barrier things though. Reviewed-by: Laurence Oberman From mboxrd@z Thu Jan 1 00:00:00 1970 From: loberman@redhat.com (Laurence Oberman) Date: Tue, 20 Mar 2018 12:51:58 -0400 Subject: [PATCH v4 1/7] scsi: hpsa: Eliminate duplicate barriers on weakly-ordered archs In-Reply-To: <1521514207-10695-2-git-send-email-okaya@codeaurora.org> References: <1521514207-10695-1-git-send-email-okaya@codeaurora.org> <1521514207-10695-2-git-send-email-okaya@codeaurora.org> Message-ID: <1521564718.13995.1.camel@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, 2018-03-19 at 22:50 -0400, Sinan Kaya wrote: > Code includes wmb() followed by writel(). writel() already has a > barrier on some architectures like arm64. > > This ends up CPU observing two barriers back to back before executing > the register write. > > Since code already has an explicit barrier call, changing writel() to > writel_relaxed(). > > Signed-off-by: Sinan Kaya > --- > ?drivers/scsi/hpsa.h | 2 +- > ?1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/scsi/hpsa.h b/drivers/scsi/hpsa.h > index 018f980..c7d7e6a 100644 > --- a/drivers/scsi/hpsa.h > +++ b/drivers/scsi/hpsa.h > @@ -599,7 +599,7 @@ static unsigned long > SA5_ioaccel_mode1_completed(struct ctlr_info *h, u8 q) > ? ?* but with current driver design this is easiest. > ? ?*/ > ? wmb(); > - writel((q << 24) | rq->current_entry, h->vaddr + > + writel_relaxed((q << 24) | rq->current_entry, h- > >vaddr + > ? IOACCEL_MODE1_CONSUMER_INDEX); > ? atomic_dec(&h->commands_outstanding); > ? } This looks like it would work for the x86_64 and arm because of how its defined architecture specific for the x86_64 and the arm64 I guess its up to Don and the driver folks and if its worth the change. I am generally not a fan of messing with these barrier things though. Reviewed-by: Laurence Oberman