[RFC,v3,02/11] scsi: ufs: qcom: Perform read back after writing REG_UFS_SYS1CLK_1US
Message ID | 20231221-ufs-reset-ensure-effect-before-delay-v3-2-2195a1b66d2e@redhat.com |
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State | New |
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Bottomley" <jejb@linux.ibm.com>, "Martin K. Petersen" <martin.petersen@oracle.com>, Hannes Reinecke <hare@suse.de>, Janek Kotas <jank@cadence.com>, Alim Akhtar <alim.akhtar@samsung.com>, Avri Altman <avri.altman@wdc.com>, Bart Van Assche <bvanassche@acm.org>, Can Guo <quic_cang@quicinc.com> Cc: Andrew Halaney <ahalaney@redhat.com>, Will Deacon <will@kernel.org>, linux-arm-msm@vger.kernel.org, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH RFC v3 02/11] scsi: ufs: qcom: Perform read back after writing REG_UFS_SYS1CLK_1US Date: Thu, 21 Dec 2023 13:09:48 -0600 Message-ID: <20231221-ufs-reset-ensure-effect-before-delay-v3-2-2195a1b66d2e@redhat.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20231221-ufs-reset-ensure-effect-before-delay-v3-0-2195a1b66d2e@redhat.com> References: <20231221-ufs-reset-ensure-effect-before-delay-v3-0-2195a1b66d2e@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: <linux-kernel.vger.kernel.org> List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org> List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" X-Mailer: b4 0.12.3 Content-Transfer-Encoding: 8bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1785919854431890289 X-GMAIL-MSGID: 1785919854431890289 |
Series |
scsi: ufs: Remove overzealous memory barriers
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Commit Message
Andrew Halaney
Dec. 21, 2023, 7:09 p.m. UTC
Currently after writing to REG_UFS_SYS1CLK_1US a mb() is used to ensure
that write has gone through to the device.
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: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations")
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
---
drivers/ufs/host/ufs-qcom.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Comments
On 12/22/2023 3:09 AM, Andrew Halaney wrote: > Currently after writing to REG_UFS_SYS1CLK_1US a mb() is used to ensure > that write has gone through to the device. > > 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: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations") > Signed-off-by: Andrew Halaney <ahalaney@redhat.com> > --- > drivers/ufs/host/ufs-qcom.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c > index 480787048e75..4c15c8a1d058 100644 > --- a/drivers/ufs/host/ufs-qcom.c > +++ b/drivers/ufs/host/ufs-qcom.c > @@ -501,7 +501,7 @@ static int ufs_qcom_cfg_timers(struct ufs_hba *hba, u32 gear, > * make sure above write gets applied before we return from > * this function. > */ > - mb(); > + ufshcd_readl(hba, REG_UFS_SYS1CLK_1US); > } > > return 0; > Reviewed-by: Can Guo <quic_cang@quicinc.com>
diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c index 480787048e75..4c15c8a1d058 100644 --- a/drivers/ufs/host/ufs-qcom.c +++ b/drivers/ufs/host/ufs-qcom.c @@ -501,7 +501,7 @@ static int ufs_qcom_cfg_timers(struct ufs_hba *hba, u32 gear, * make sure above write gets applied before we return from * this function. */ - mb(); + ufshcd_readl(hba, REG_UFS_SYS1CLK_1US); } return 0;