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 6.6-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-cdns-pltfrm-perform-read-back-after-writing.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 5ff19e30be8cb564378571ec55c5f0722e3068d8
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 2491e7e870283..56014ef302b49 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;
}
