mmc: mediatek: perfer to use rise edge latching

in our host design, rise edge latching is more stable than fall edge
latching. so that if rise edge has enough margin, no need scan fall edge.
Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/mtk-sd.c

@@ -1328,7 +1328,7 @@ static int msdc_tune_response(struct mmc_host *mmc, u32 opcode)
 {
 	struct msdc_host *host = mmc_priv(mmc);
 	u32 rise_delay = 0, fall_delay = 0;
-	struct msdc_delay_phase final_rise_delay, final_fall_delay;
+	struct msdc_delay_phase final_rise_delay, final_fall_delay = { 0,};
 	u8 final_delay, final_maxlen;
 	int cmd_err;
 	int i;
@@ -1341,6 +1341,11 @@ static int msdc_tune_response(struct mmc_host *mmc, u32 opcode)
 		if (!cmd_err)
 			rise_delay |= (1 << i);
 	}
+	final_rise_delay = get_best_delay(host, rise_delay);
+	/* if rising edge has enough margin, then do not scan falling edge */
+	if (final_rise_delay.maxlen >= 10 ||
+	    (final_rise_delay.start == 0 && final_rise_delay.maxlen >= 4))
+		goto skip_fall;
 
 	sdr_set_bits(host->base + MSDC_IOCON, MSDC_IOCON_RSPL);
 	for (i = 0; i < PAD_DELAY_MAX; i++) {
@@ -1350,10 +1355,9 @@ static int msdc_tune_response(struct mmc_host *mmc, u32 opcode)
 		if (!cmd_err)
 			fall_delay |= (1 << i);
 	}
-
-	final_rise_delay = get_best_delay(host, rise_delay);
 	final_fall_delay = get_best_delay(host, fall_delay);
 
+skip_fall:
 	final_maxlen = max(final_rise_delay.maxlen, final_fall_delay.maxlen);
 	if (final_maxlen == final_rise_delay.maxlen) {
 		sdr_clr_bits(host->base + MSDC_IOCON, MSDC_IOCON_RSPL);
@@ -1374,7 +1378,7 @@ static int msdc_tune_data(struct mmc_host *mmc, u32 opcode)
 {
 	struct msdc_host *host = mmc_priv(mmc);
 	u32 rise_delay = 0, fall_delay = 0;
-	struct msdc_delay_phase final_rise_delay, final_fall_delay;
+	struct msdc_delay_phase final_rise_delay, final_fall_delay = { 0,};
 	u8 final_delay, final_maxlen;
 	int i, ret;
 
@@ -1387,6 +1391,11 @@ static int msdc_tune_data(struct mmc_host *mmc, u32 opcode)
 		if (!ret)
 			rise_delay |= (1 << i);
 	}
+	final_rise_delay = get_best_delay(host, rise_delay);
+	/* if rising edge has enough margin, then do not scan falling edge */
+	if (final_rise_delay.maxlen >= 10 ||
+	    (final_rise_delay.start == 0 && final_rise_delay.maxlen >= 4))
+		goto skip_fall;
 
 	sdr_set_bits(host->base + MSDC_IOCON, MSDC_IOCON_DSPL);
 	sdr_set_bits(host->base + MSDC_IOCON, MSDC_IOCON_W_DSPL);
@@ -1397,14 +1406,10 @@ static int msdc_tune_data(struct mmc_host *mmc, u32 opcode)
 		if (!ret)
 			fall_delay |= (1 << i);
 	}
-
-	final_rise_delay = get_best_delay(host, rise_delay);
 	final_fall_delay = get_best_delay(host, fall_delay);
 
+skip_fall:
 	final_maxlen = max(final_rise_delay.maxlen, final_fall_delay.maxlen);
-	/* Rising edge is more stable, prefer to use it */
-	if (final_rise_delay.maxlen >= 10)
-		final_maxlen = final_rise_delay.maxlen;
 	if (final_maxlen == final_rise_delay.maxlen) {
 		sdr_clr_bits(host->base + MSDC_IOCON, MSDC_IOCON_DSPL);
 		sdr_clr_bits(host->base + MSDC_IOCON, MSDC_IOCON_W_DSPL);