[PATCH v3 08/20] mmc: am654_sdhci: Add support for software tuning

[Aswath Govindraju <a-govindraju@ti.com>]

From: Faiz Abbas <faiz_abbas@ti.com>

With the new SW tuning App note[1], a custom tuning algorithm is
required for eMMC HS200, HS400 and SD card UHS modes. The algorithm
involves running through the 32 possible input tap delay values and
sending the appropriate tuning command (CMD19/21) for each of them
to get a fail or pass result for each of the values. Typically, the
range will have a small contiguous failing window. Considering the
tuning range as a circular buffer, the algorithm then sets a final
tuned value directly opposite to the failing window.

[1] https://www.ti.com/lit/pdf/spract9

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
---
 drivers/mmc/am654_sdhci.c | 45 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/mmc/am654_sdhci.c b/drivers/mmc/am654_sdhci.c
index e86ef1a8b218..9549420c6582 100644
--- a/drivers/mmc/am654_sdhci.c
+++ b/drivers/mmc/am654_sdhci.c
@@ -9,6 +9,7 @@
 #include <common.h>
 #include <dm.h>
 #include <malloc.h>
+#include <mmc.h>
 #include <power-domain.h>
 #include <regmap.h>
 #include <sdhci.h>
@@ -368,7 +369,48 @@ static int am654_sdhci_deferred_probe(struct sdhci_host *host)
 	return sdhci_probe(dev);
 }
 
+#ifdef MMC_SUPPORTS_TUNING
+#define ITAP_MAX	32
+static int am654_sdhci_execute_tuning(struct mmc *mmc, u8 opcode)
+{
+	struct udevice *dev = mmc->dev;
+	struct am654_sdhci_plat *plat = dev_get_plat(dev);
+	int cur_val, prev_val = 1, fail_len = 0, pass_window = 0, pass_len;
+	u32 itap;
+
+	/* Enable ITAPDLY */
+	regmap_update_bits(plat->base, PHY_CTRL4, ITAPDLYENA_MASK,
+			   1 << ITAPDLYENA_SHIFT);
+
+	for (itap = 0; itap < ITAP_MAX; itap++) {
+		am654_sdhci_write_itapdly(plat, itap);
+
+		cur_val = !mmc_send_tuning(mmc, opcode, NULL);
+		if (cur_val && !prev_val)
+			pass_window = itap;
+
+		if (!cur_val)
+			fail_len++;
+
+		prev_val = cur_val;
+	}
+	/*
+	 * Having determined the length of the failing window and start of
+	 * the passing window calculate the length of the passing window and
+	 * set the final value halfway through it considering the range as a
+	 * circular buffer
+	 */
+	pass_len = ITAP_MAX - fail_len;
+	itap = (pass_window + (pass_len >> 1)) % ITAP_MAX;
+	am654_sdhci_write_itapdly(plat, itap);
+
+	return 0;
+}
+#endif
 const struct sdhci_ops am654_sdhci_ops = {
+#ifdef MMC_SUPPORTS_TUNING
+	.platform_execute_tuning = am654_sdhci_execute_tuning,
+#endif
 	.deferred_probe		= am654_sdhci_deferred_probe,
 	.set_ios_post		= &am654_sdhci_set_ios_post,
 	.set_control_reg	= &am654_sdhci_set_control_reg,
@@ -408,6 +450,9 @@ static int j721e_4bit_sdhci_set_ios_post(struct sdhci_host *host)
 }
 
 const struct sdhci_ops j721e_4bit_sdhci_ops = {
+#ifdef MMC_SUPPORTS_TUNING
+	.platform_execute_tuning = am654_sdhci_execute_tuning,
+#endif
 	.deferred_probe		= am654_sdhci_deferred_probe,
 	.set_ios_post		= &j721e_4bit_sdhci_set_ios_post,
 };
-- 
2.17.1