scsi: ufs-mediatek: Fix imprecise waiting time for ref-clk control

Currently ref-clk control timeout is implemented by jiffies. However
jiffies is not accurate enough thus "false timeout" may happen.

Use more accurate delay mechanism instead, i.e. ktime.

Link: https://lore.kernel.org/r/20200601104646.15436-2-stanley.chu@mediatek.comReviewed-by: Andy Teng <andy.teng@mediatek.com>
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ufs/ufs-mediatek.c

@@ -120,7 +120,7 @@ static int ufs_mtk_setup_ref_clk(struct ufs_hba *hba, bool on)
 {
 	struct ufs_mtk_host *host = ufshcd_get_variant(hba);
 	struct arm_smccc_res res;
-	unsigned long timeout;
+	ktime_t timeout, time_checked;
 	u32 value;
 
 	if (host->ref_clk_enabled == on)
@@ -135,8 +135,9 @@ static int ufs_mtk_setup_ref_clk(struct ufs_hba *hba, bool on)
 	}
 
 	/* Wait for ack */
-	timeout = jiffies + msecs_to_jiffies(REFCLK_REQ_TIMEOUT_MS);
+	timeout = ktime_add_us(ktime_get(), REFCLK_REQ_TIMEOUT_US);
 	do {
+		time_checked = ktime_get();
 		value = ufshcd_readl(hba, REG_UFS_REFCLK_CTRL);
 
 		/* Wait until ack bit equals to req bit */
@@ -144,7 +145,7 @@ static int ufs_mtk_setup_ref_clk(struct ufs_hba *hba, bool on)
 			goto out;
 
 		usleep_range(100, 200);
-	} while (time_before(jiffies, timeout));
+	} while (ktime_before(time_checked, timeout));
 
 	dev_err(hba->dev, "missing ack of refclk req, reg: 0x%x\n", value);
 

drivers/scsi/ufs/ufs-mediatek.h

@@ -28,7 +28,7 @@
 #define REFCLK_REQUEST              BIT(0)
 #define REFCLK_ACK                  BIT(1)
 
-#define REFCLK_REQ_TIMEOUT_MS       3
+#define REFCLK_REQ_TIMEOUT_US       3000
 
 /*
  * Vendor specific pre-defined parameters