scsi: ufs-qcom: Delay specific time before gate ref clk

After enter hibern8, as UFS JEDEC ver 3.0 requires, a specific gating wait
time is required before disable the device reference clock. If it is not
specified, use the old delay.

Link: https://lore.kernel.org/r/1581392451-28743-8-git-send-email-cang@codeaurora.orgReviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Reviewed-by: Hongwu Su <hongwus@codeaurora.org>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ufs/ufs-qcom.c

@@ -843,11 +843,27 @@ static void ufs_qcom_dev_ref_clk_ctrl(struct ufs_qcom_host *host, bool enable)
 		/*
 		 * If we are here to disable this clock it might be immediately
 		 * after entering into hibern8 in which case we need to make
-		 * sure that device ref_clk is active at least 1us after the
+		 * sure that device ref_clk is active for specific time after
 		 * hibern8 enter.
 		 */
-		if (!enable)
-			udelay(1);
+		if (!enable) {
+			unsigned long gating_wait;
+
+			gating_wait = host->hba->dev_info.clk_gating_wait_us;
+			if (!gating_wait) {
+				udelay(1);
+			} else {
+				/*
+				 * bRefClkGatingWaitTime defines the minimum
+				 * time for which the reference clock is
+				 * required by device during transition from
+				 * HS-MODE to LS-MODE or HIBERN8 state. Give it
+				 * more delay to be on the safe side.
+				 */
+				gating_wait += 10;
+				usleep_range(gating_wait, gating_wait + 10);
+			}
+		}
 
 		writel_relaxed(temp, host->dev_ref_clk_ctrl_mmio);