scsi: ufs: core: Perform read back after disabling UIC_COMMAND_COMPL

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>

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 268fcfebd7bd3263b13a38a11ac8e122410109e4..dfa4f827766ac1356d9ba18c36619f9be369d2c8 100644 (file)
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -4287,7 +4287,7 @@ 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);