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Message-ID: <107abfd9-b3f5-4495-b86c-070ed354d2bb@quicinc.com>
Date: Fri, 22 Dec 2023 16:20:21 +0800
From: Can Guo <quic_cang@...cinc.com>
To: Andrew Halaney <ahalaney@...hat.com>, Andy Gross <agross@...nel.org>,
Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio
<konrad.dybcio@...aro.org>,
Manivannan Sadhasivam <mani@...nel.org>,
"James
E.J. Bottomley" <jejb@...ux.ibm.com>,
"Martin K. Petersen"
<martin.petersen@...cle.com>,
Hannes Reinecke <hare@...e.de>, Janek Kotas
<jank@...ence.com>,
Alim Akhtar <alim.akhtar@...sung.com>,
Avri Altman
<avri.altman@....com>,
Bart Van Assche <bvanassche@....org>
CC: Will Deacon <will@...nel.org>, <linux-arm-msm@...r.kernel.org>,
<linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v3 03/11] scsi: ufs: qcom: Perform read back after
writing testbus config
On 12/22/2023 3:09 AM, Andrew Halaney wrote:
> Currently, the testbus configuration is written and 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: 9c46b8676271 ("scsi: ufs-qcom: dump additional testbus registers")
> Signed-off-by: Andrew Halaney <ahalaney@...hat.com>
> ---
> drivers/ufs/host/ufs-qcom.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
> index 4c15c8a1d058..6df2ab3b6f23 100644
> --- a/drivers/ufs/host/ufs-qcom.c
> +++ b/drivers/ufs/host/ufs-qcom.c
> @@ -1332,6 +1332,9 @@ static void ufs_qcom_enable_test_bus(struct ufs_qcom_host *host)
> ufshcd_rmwl(host->hba, UFS_REG_TEST_BUS_EN,
> UFS_REG_TEST_BUS_EN, REG_UFS_CFG1);
> ufshcd_rmwl(host->hba, TEST_BUS_EN, TEST_BUS_EN, REG_UFS_CFG1);
> +
> + /* dummy read to ensure this has been enabled prior to returning */
> + ufshcd_readl(host->hba, REG_UFS_CFG1);
> }
>
> static void ufs_qcom_get_default_testbus_cfg(struct ufs_qcom_host *host)
> @@ -1429,11 +1432,6 @@ int ufs_qcom_testbus_config(struct ufs_qcom_host *host)
> (u32)host->testbus.select_minor << offset,
> reg);
> ufs_qcom_enable_test_bus(host);
> - /*
> - * Make sure the test bus configuration is
> - * committed before returning.
> - */
> - mb();
>
> return 0;
> }
>
Reviewed-by: Can Guo <quic_cang@...cinc.com>
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