This is a note to let you know that I've just added the patch titled
scsi: ufs: qcom: Perform read back after writing reset bit
to the 5.4-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-reset-.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit cbadfcaec24aa8be728c206e253238170e0ef903
Author: Andrew Halaney <ahalaney@xxxxxxxxxx>
Date: Fri Mar 29 15:46:43 2024 -0500
scsi: ufs: qcom: Perform read back after writing reset bit
[ Upstream commit c4d28e06b0c94636f6e35d003fa9ebac0a94e1ae ]
Currently, the reset bit for the UFS provided reset controller (used by its
phy) is written to, and then a mb() happens to try and ensure that hit the
device. Immediately afterwards a usleep_range() occurs.
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. By doing so and
guaranteeing the ordering against the immediately following usleep_range(),
the mb() can safely be removed.
Fixes: 81c0fc51b7a7 ("ufs-qcom: add support for Qualcomm Technologies Inc platforms")
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
Reviewed-by: Can Guo <quic_cang@xxxxxxxxxxx>
Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240329-ufs-reset-ensure-effect-before-delay-v5-1-181252004586@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.h b/drivers/scsi/ufs/ufs-qcom.h
index d401f174bb70b..3220345682a9b 100644
--- a/drivers/scsi/ufs/ufs-qcom.h
+++ b/drivers/scsi/ufs/ufs-qcom.h
@@ -155,10 +155,10 @@ static inline void ufs_qcom_assert_reset(struct ufs_hba *hba)
1 << OFFSET_UFS_PHY_SOFT_RESET, REG_UFS_CFG1);
/*
- * Make sure assertion of ufs phy reset is written to
- * register before returning
+ * Dummy read to ensure the write takes effect before doing any sort
+ * of delay
*/
- mb();
+ ufshcd_readl(hba, REG_UFS_CFG1);
}
static inline void ufs_qcom_deassert_reset(struct ufs_hba *hba)
@@ -167,10 +167,10 @@ static inline void ufs_qcom_deassert_reset(struct ufs_hba *hba)
0 << OFFSET_UFS_PHY_SOFT_RESET, REG_UFS_CFG1);
/*
- * Make sure de-assertion of ufs phy reset is written to
- * register before returning
+ * Dummy read to ensure the write takes effect before doing any sort
+ * of delay
*/
- mb();
+ ufshcd_readl(hba, REG_UFS_CFG1);
}
struct ufs_qcom_bus_vote {
