This is a note to let you know that I've just added the patch titled
scsi: ufs: qcom: Perform read back after writing CGC enable
to the 5.15-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-cgc-en.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 423df859f08e5441bebd3187aa43a2c69fa2aa55
Author: Andrew Halaney <ahalaney@xxxxxxxxxx>
Date: Fri Mar 29 15:46:47 2024 -0500
scsi: ufs: qcom: Perform read back after writing CGC enable
[ Upstream commit d9488511b3ac7eb48a91bc5eded7027525525e03 ]
Currently, the CGC enable bit is written 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
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.
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
Reviewed-by: Can Guo <quic_cang@xxxxxxxxxxx>
Fixes: 81c0fc51b7a7 ("ufs-qcom: add support for Qualcomm Technologies Inc platforms")
Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240329-ufs-reset-ensure-effect-before-delay-v5-5-181252004586@xxxxxxxxxx
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/scsi/ufs/ufs-qcom.c b/drivers/scsi/ufs/ufs-qcom.c
index ce45f3e8a35c3..361df2a2db5bf 100644
--- a/drivers/scsi/ufs/ufs-qcom.c
+++ b/drivers/scsi/ufs/ufs-qcom.c
@@ -353,7 +353,7 @@ static void ufs_qcom_enable_hw_clk_gating(struct ufs_hba *hba)
REG_UFS_CFG2);
/* Ensure that HW clock gating is enabled before next operations */
- mb();
+ ufshcd_readl(hba, REG_UFS_CFG2);
}
static int ufs_qcom_hce_enable_notify(struct ufs_hba *hba,
