Patch "scsi: ufs: qcom: Perform read back after writing unipro mode" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    scsi: ufs: qcom: Perform read back after writing unipro mode

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     scsi-ufs-qcom-perform-read-back-after-writing-unipro.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 76f6d013f5f4c954cee747eeef10707c802f00bc
Author: Andrew Halaney <ahalaney@xxxxxxxxxx>
Date:   Fri Mar 29 15:46:46 2024 -0500

    scsi: ufs: qcom: Perform read back after writing unipro mode
    
    [ Upstream commit 823150ecf04f958213cf3bf162187cd1a91c885c ]
    
    Currently, the QUNIPRO_SEL bit is written to and then an mb() is used to
    ensure that completes before continuing.
    
    mb() ensures 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
    
    But, there's really no reason to even ensure completion before
    continuing. The only requirement here is that this write is ordered to this
    endpoint (which readl()/writel() guarantees already). For that reason the
    mb() can be dropped altogether without anything forcing completion.
    
    Fixes: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations")
    Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240329-ufs-reset-ensure-effect-before-delay-v5-4-181252004586@xxxxxxxxxx
    Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
    Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
index 559b4cab16a3e..1f2a64d797c79 100644
--- a/drivers/ufs/host/ufs-qcom.c
+++ b/drivers/ufs/host/ufs-qcom.c
@@ -373,9 +373,6 @@ static void ufs_qcom_select_unipro_mode(struct ufs_qcom_host *host)
 
 	if (host->hw_ver.major >= 0x05)
 		ufshcd_rmwl(host->hba, QUNIPRO_G4_SEL, 0, REG_UFS_CFG0);
-
-	/* make sure above configuration is applied before we return */
-	mb();
 }
 
 /*




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