mmc: sdhci-esdhc-imx: optimize the manual tuing logic to get the best timing

Current manual tuning logic only get the first pass window, but
this pass window maybe not the best pass window.

Now find all the pass window, and chose the largest pass window,
and use the average value of this largest pass window to get the
best timing.

Signed-off-by: Haibo Chen <[e-mail]>
Acked-by: Adrian Hunter <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/sdhci-esdhc-imx.c

···
 	writel(reg, host->ioaddr + ESDHC_MIX_CTRL);
 }
 
+/*
+ * find the largest pass window, and use the average delay of this
+ * largest window to get the best timing.
+ */
 static int esdhc_executing_tuning(struct sdhci_host *host, u32 opcode)
 {
 	int min, max, avg, ret;
+	int win_length, target_min, target_max, target_win_length;
 
-	/* find the mininum delay first which can pass tuning */
 	min = ESDHC_TUNE_CTRL_MIN;
-	while (min < ESDHC_TUNE_CTRL_MAX) {
-		esdhc_prepare_tuning(host, min);
-		if (!mmc_send_tuning(host->mmc, opcode, NULL))
-			break;
-		min += ESDHC_TUNE_CTRL_STEP;
-	}
-
-	/* find the maxinum delay which can not pass tuning */
-	max = min + ESDHC_TUNE_CTRL_STEP;
+	max = ESDHC_TUNE_CTRL_MIN;
+	target_win_length = 0;
 	while (max < ESDHC_TUNE_CTRL_MAX) {
-		esdhc_prepare_tuning(host, max);
-		if (mmc_send_tuning(host->mmc, opcode, NULL)) {
-			max -= ESDHC_TUNE_CTRL_STEP;
-			break;
+		/* find the mininum delay first which can pass tuning */
+		while (min < ESDHC_TUNE_CTRL_MAX) {
+			esdhc_prepare_tuning(host, min);
+			if (!mmc_send_tuning(host->mmc, opcode, NULL))
+				break;
+			min += ESDHC_TUNE_CTRL_STEP;
 		}
-		max += ESDHC_TUNE_CTRL_STEP;
+
+		/* find the maxinum delay which can not pass tuning */
+		max = min + ESDHC_TUNE_CTRL_STEP;
+		while (max < ESDHC_TUNE_CTRL_MAX) {
+			esdhc_prepare_tuning(host, max);
+			if (mmc_send_tuning(host->mmc, opcode, NULL)) {
+				max -= ESDHC_TUNE_CTRL_STEP;
+				break;
+			}
+			max += ESDHC_TUNE_CTRL_STEP;
+		}
+
+		win_length = max - min + 1;
+		/* get the largest pass window */
+		if (win_length > target_win_length) {
+			target_win_length = win_length;
+			target_min = min;
+			target_max = max;
+		}
+
+		/* continue to find the next pass window */
+		min = max + ESDHC_TUNE_CTRL_STEP;
 	}
 
 	/* use average delay to get the best timing */
-	avg = (min + max) / 2;
+	avg = (target_min + target_max) / 2;
 	esdhc_prepare_tuning(host, avg);
 	ret = mmc_send_tuning(host->mmc, opcode, NULL);
 	esdhc_post_tuning(host);