mmc: renesas_sdhi: improve TAP selection if all TAPs are good

When tuning HS400, if all TAPS are good, we can utilize the SMPCMP
register to select the optimal TAP. For that, we populate a second
bitmap with SMPCMP results and query it in case the regular bitmap is
full (= all good).
Signed-off-by: Masaharu Hayakawa <masaharu.hayakawa.ry@renesas.com>
Signed-off-by: Takeshi Saito <takeshi.saito.xv@renesas.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20200408094638.10375-4-wsa+renesas@sang-engineering.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/renesas_sdhi.h

@@ -61,6 +61,8 @@ struct renesas_sdhi {
 
 	/* Tuning values: 1 for success, 0 for failure */
 	DECLARE_BITMAP(taps, BITS_PER_LONG);
+	/* Sampling data comparison: 1 for match, 0 for mismatch */
+	DECLARE_BITMAP(smpcmp, BITS_PER_LONG);
 	unsigned int tap_num;
 	unsigned long tap_set;
 };

drivers/mmc/host/renesas_sdhi_core.c

@@ -428,7 +428,8 @@ static int renesas_sdhi_select_tuning(struct tmio_mmc_host *host)
 {
 	struct renesas_sdhi *priv = host_to_priv(host);
 	unsigned int tap_start = 0, tap_end = 0, tap_cnt = 0, rs, re, i;
-	unsigned int taps_size = priv->tap_num * 2;
+	unsigned int taps_size = priv->tap_num * 2, min_tap_row;
+	unsigned long *bitmap;
 
 	priv->doing_tune = false;
 	sd_scc_write32(host, priv, SH_MOBILE_SDHI_SCC_RVSREQ, 0);
@@ -443,6 +444,21 @@ static int renesas_sdhi_select_tuning(struct tmio_mmc_host *host)
 
 		if (!test_bit(i, priv->taps))
 			clear_bit(i + offset, priv->taps);
+
+		if (!test_bit(i, priv->smpcmp))
+			clear_bit(i + offset, priv->smpcmp);
+	}
+
+	/*
+	 * If all TAP are OK, the sampling clock position is selected by
+	 * identifying the change point of data.
+	 */
+	if (bitmap_full(priv->taps, taps_size)) {
+		bitmap = priv->smpcmp;
+		min_tap_row = 1;
+	} else {
+		bitmap = priv->taps;
+		min_tap_row = SH_MOBILE_SDHI_MIN_TAP_ROW;
 	}
 
 	/*
@@ -450,7 +466,7 @@ static int renesas_sdhi_select_tuning(struct tmio_mmc_host *host)
 	 * is at least SH_MOBILE_SDHI_MIN_TAP_ROW probes long then use the
 	 * center index as the tap, otherwise bail out.
 	 */
-	bitmap_for_each_set_region(priv->taps, rs, re, 0, taps_size) {
+	bitmap_for_each_set_region(bitmap, rs, re, 0, taps_size) {
 		if (re - rs > tap_cnt) {
 			tap_end = re;
 			tap_start = rs;
@@ -458,7 +474,7 @@ static int renesas_sdhi_select_tuning(struct tmio_mmc_host *host)
 		}
 	}
 
-	if (tap_cnt >= SH_MOBILE_SDHI_MIN_TAP_ROW)
+	if (tap_cnt >= min_tap_row)
 		priv->tap_set = (tap_start + tap_end) / 2 % priv->tap_num;
 	else
 		return -EIO;
@@ -491,6 +507,7 @@ static int renesas_sdhi_execute_tuning(struct tmio_mmc_host *host, u32 opcode)
 
 	priv->doing_tune = true;
 	bitmap_zero(priv->taps, priv->tap_num * 2);
+	bitmap_zero(priv->smpcmp, priv->tap_num * 2);
 
 	/* Issue CMD19 twice for each tap */
 	for (i = 0; i < 2 * priv->tap_num; i++) {
@@ -499,6 +516,9 @@ static int renesas_sdhi_execute_tuning(struct tmio_mmc_host *host, u32 opcode)
 
 		if (mmc_send_tuning(host->mmc, opcode, NULL) == 0)
 			set_bit(i, priv->taps);
+
+		if (sd_scc_read32(host, priv, SH_MOBILE_SDHI_SCC_SMPCMP) == 0)
+			set_bit(i, priv->smpcmp);
 	}
 
 	return renesas_sdhi_select_tuning(host);