[PATCH 6.1 111/473] scsi: ufs: core: Perform read back after disabling UIC_COMMAND_COMPL

Greg Kroah-Hartman
2024-06-06T14:13:53Z

From: Andrew Halaney <ahalaney@redhat.com>

[ 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@acm.org>
Reviewed-by: Can Guo <quic_cang@quicinc.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Link: https://lore.kernel.org/r/20240329-ufs-reset-ensure-effect-before-delay-v5-9-181252004586@redhat.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 f54260d7873f1..5922cb5a1de0d 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -4074,7 +4074,7 @@ 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