From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7538D5228; Wed, 27 Dec 2023 06:18:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="m+llo1X9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B170EC433C7; Wed, 27 Dec 2023 06:18:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1703657927; bh=f12A6QbCQVUZfP169hKVQL7gHb1oq0RYqXw5nplJHNY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=m+llo1X9SNv2aJzA5txMtfEhY3Fkia9Pm/Zwr96hdH3lt+tuFl+JqYzSIeMD25PbD GeB4gyGUquDV2Vk9yEN3KE2jxkeY8kCp6g2VMNZjMuhV9qVWFjk4o1wDIDHYqNnbtX 8dUxEMwuNxiK6BU6Yvfh1ONbl0bY2GcJqRcYZ6vy5X4GnKNEM+INpF31TIRH320YjT PAlfmfqMR9kWK1vppqszh6nG0c/1f9feopI2vi5MT4p5NaQiRQ6CWMaZf9B1NeBgRR 4i4jh76GazY0fKnGcL5JtrNNf1vXZuf3vmNdnEjUr/zEXxHvIxJK9vcTfeOKXB/ReX h3UPKA0S/xGGg== Date: Wed, 27 Dec 2023 11:48:37 +0530 From: Manivannan Sadhasivam To: Andrew Halaney Cc: Andy Gross , Bjorn Andersson , Konrad Dybcio , Manivannan Sadhasivam , "James E.J. Bottomley" , "Martin K. Petersen" , Hannes Reinecke , Janek Kotas , Alim Akhtar , Avri Altman , Bart Van Assche , Can Guo , Will Deacon , linux-arm-msm@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC v3 10/11] scsi: ufs: core: Perform read back to commit doorbell Message-ID: <20231227061837.GH2814@thinkpad> References: <20231221-ufs-reset-ensure-effect-before-delay-v3-0-2195a1b66d2e@redhat.com> <20231221-ufs-reset-ensure-effect-before-delay-v3-10-2195a1b66d2e@redhat.com> Precedence: bulk X-Mailing-List: linux-scsi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20231221-ufs-reset-ensure-effect-before-delay-v3-10-2195a1b66d2e@redhat.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 Reviewed-by: Manivannan Sadhasivam - 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 > -- மணிவண்ணன் சதாசிவம்