Patch "scsi: ufs: cdns-pltfrm: Perform read back after writing HCLKDIV" has been added to the 6.1-stable tree

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

    scsi: ufs: cdns-pltfrm: Perform read back after writing HCLKDIV

to the 6.1-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-cdns-pltfrm-perform-read-back-after-writing.patch
and it can be found in the queue-6.1 subdirectory.

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



commit 28ab8bbb37519e6f02b38f20dc0d55b07c5f320f
Author: Andrew Halaney <ahalaney@xxxxxxxxxx>
Date:   Fri Mar 29 15:46:48 2024 -0500

    scsi: ufs: cdns-pltfrm: Perform read back after writing HCLKDIV
    
    [ Upstream commit b715c55daf598aac8fa339048e4ca8a0916b332e ]
    
    Currently, HCLKDIV is written to and then completed with an mb().
    
    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
    
    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")
    Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
    Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240329-ufs-reset-ensure-effect-before-delay-v5-6-181252004586@xxxxxxxxxx
    Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx>
    Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/ufs/host/cdns-pltfrm.c b/drivers/ufs/host/cdns-pltfrm.c
index e05c0ae64eea4..38a238eaa2133 100644
--- a/drivers/ufs/host/cdns-pltfrm.c
+++ b/drivers/ufs/host/cdns-pltfrm.c
@@ -137,7 +137,7 @@ 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;
 }




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