[PATCH 6.9 133/427] scsi: ufs: core: Perform read back after disabling UIC_COMMAND_COMPL

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6.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Halaney <ahalaney@xxxxxxxxxx>

[ Upstream commit 4bf3855497b60765ca03b983d064b25e99b97657 ]

Currently, the UIC_COMMAND_COMPL interrupt is disabled and a wmb() is used
to complete the register write before any following writes.

wmb() ensures the writes complete in that order, 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 wmb()'s
purpose wasn't to add extra ordering (on top of the ordering guaranteed by
writel()/readl()), it can safely be removed.

Fixes: d75f7fe495cf ("scsi: ufs: reduce the interrupts for power mode change requests")
Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx>
Reviewed-by: Can Guo <quic_cang@xxxxxxxxxxx>
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-v5-9-181252004586@xxxxxxxxxx
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/ufs/core/ufshcd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 5ade57c5a6f4f..1322a9c318cff 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -4289,7 +4289,7 @@ static int ufshcd_uic_pwr_ctrl(struct ufs_hba *hba, struct uic_command *cmd)
 		 * Make sure UIC command completion interrupt is disabled before
 		 * issuing UIC command.
 		 */
-		wmb();
+		ufshcd_readl(hba, REG_INTERRUPT_ENABLE);
 		reenable_intr = true;
 	}
 	spin_unlock_irqrestore(hba->host->host_lock, flags);
-- 
2.43.0







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