[PATCH 6.1 104/473] scsi: ufs: qcom: Perform read back after writing REG_UFS_SYS1CLK_1US

Greg Kroah-Hartman
2024-06-06T14:13:48Z

From: Andrew Halaney <ahalaney@redhat.com>

[ Upstream commit a862fafa263aea0f427d51aca6ff7fd9eeaaa8bd ]

Currently after writing to REG_UFS_SYS1CLK_1US a mb() is used to ensure
that write has gone through to the device.

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: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations")
Reviewed-by: Can Guo <quic_cang@quicinc.com>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Link: https://lore.kernel.org/r/20240329-ufs-reset-ensure-effect-before-delay-v5-2-181252004586@redhat.com
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/ufs/host/ufs-qcom.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
index 8ad1415e10b63..a5d981d3dd6be 100644
--- a/drivers/ufs/host/ufs-qcom.c
+++ b/drivers/ufs/host/ufs-qcom.c
@@ -432,7 +432,7 @@ static int ufs_qcom_cfg_timers(struct ufs_hba *hba, u32 gear,
* make sure above write gets applied before we return from
* this function.
*/
- mb();
+ ufshcd_readl(hba, REG_UFS_SYS1CLK_1US);
}

if (ufs_qcom_cap_qunipro(host))
--
2.43.0