6.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Andrew Halaney <ahalaney@xxxxxxxxxx>
[ 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>
---
drivers/ufs/host/ufs-qcom.c | 3 ---
1 file changed, 3 deletions(-)
diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
index 8aa55ed45d8e0..cef410f31f449 100644
--- a/drivers/ufs/host/ufs-qcom.c
+++ b/drivers/ufs/host/ufs-qcom.c
@@ -284,9 +284,6 @@ 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();
}
/*
--
2.43.0
