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 055841FC4; Wed, 27 Dec 2023 06:06:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="erUhCOiV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B57EBC433C8; Wed, 27 Dec 2023 06:06:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1703657179; bh=yJBV8w8RZHiR2mOsBa+bvaeX3R1+l1q2z/HMcJGxe1A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=erUhCOiVDZ8ZGOD2dFadIuPeUwDeLeCknS2Tmv6b0xfozgYy9/+ZVvT+kj7qK+pXu sK0W65d7m8dybqO6JNYt0q4oufs9gMQm9w8zYDFE3GIw9vzH93O2qFKvuV3Mzu50/Q PJj3/sQZ0FU01nTqi2uGF/oZBFoV6NNeOJANQrDRVMKKS6Hr5gXHPNmqUYngnNrn3G vSr3E/EzP+ds70BRyG9ygfVPeirmzMcmBI7z1LxP5anGYdFj9LG1FcMGIqid3cXaDU 4v1Lb8pHxJlNWrcT7xBVIz5Pzd3bqLZsx6cGqEtdrIIu3wP6xo/+gBw3+B2ZZiYVS1 nJO7MzhNrmLoA== Date: Wed, 27 Dec 2023 11:36:07 +0530 From: Manivannan Sadhasivam To: Andrew Halaney Cc: Andy Gross , Bjorn Andersson , Konrad Dybcio , "James E.J. Bottomley" , "Martin K. Petersen" , Yaniv Gardi , Dov Levenglick , Hannes Reinecke , Subhash Jadavani , Gilad Broner , Venkat Gopalakrishnan , Janek Kotas , Alim Akhtar , Avri Altman , Bart Van Assche , Anjana Hari , Dolev Raviv , Can Guo , Will Deacon , linux-arm-msm@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC v2 06/11] scsi: ufs: cdns-pltfrm: Perform read back after writing HCLKDIV Message-ID: <20231227060607.GD2814@thinkpad> References: <20231221-ufs-reset-ensure-effect-before-delay-v2-0-75af2a9bae51@redhat.com> <20231221-ufs-reset-ensure-effect-before-delay-v2-6-75af2a9bae51@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-v2-6-75af2a9bae51@redhat.com> On Thu, Dec 21, 2023 at 12:25:23PM -0600, Andrew Halaney wrote: > Currently, HCLKDIV is written to and then completed with an mb(). > > mb() ensure that the write completes, 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 mb()'s > purpose wasn't to add extra ordering (on top of the ordering guaranteed > by writel()/readl()), it can safely be removed. > > Fixes: d90996dae8e4 ("scsi: ufs: Add UFS platform driver for Cadence UFS") > Signed-off-by: Andrew Halaney Reviewed-by: Manivannan Sadhasivam - Mani > --- > drivers/ufs/host/cdns-pltfrm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/ufs/host/cdns-pltfrm.c b/drivers/ufs/host/cdns-pltfrm.c > index bb30267da471..66811d8d1929 100644 > --- a/drivers/ufs/host/cdns-pltfrm.c > +++ b/drivers/ufs/host/cdns-pltfrm.c > @@ -136,7 +136,7 @@ static int cdns_ufs_set_hclkdiv(struct ufs_hba *hba) > * Make sure the register was updated, > * UniPro layer will not work with an incorrect value. > */ > - mb(); > + ufshcd_readl(hba, CDNS_UFS_REG_HCLKDIV); > > return 0; > } > > -- > 2.43.0 > -- மணிவண்ணன் சதாசிவம்