[PATCH 5/6] mmc: sdhci_am654: Add support for software tuning

[Faiz Abbas]

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 at ti.com>
---
 drivers/mmc/host/sdhci_am654.c | 41 ++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/sdhci_am654.c
index 1213b711e60a..5af7638ad606 100644
--- a/drivers/mmc/host/sdhci_am654.c
+++ b/drivers/mmc/host/sdhci_am654.c
@@ -396,7 +396,46 @@ static u32 sdhci_am654_cqhci_irq(struct sdhci_host *host, u32 intmask)
 	return 0;
 }
 
+#define ITAP_MAX	32
+static int sdhci_am654_platform_execute_tuning(struct sdhci_host *host,
+					       u32 opcode)
+{
+	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
+	struct sdhci_am654_data *sdhci_am654 = sdhci_pltfm_priv(pltfm_host);
+	int cur_val, prev_val = 1, fail_len = 0, pass_window = 0, pass_len;
+	u32 itap;
+
+	/* Enable ITAPDLY */
+	regmap_update_bits(sdhci_am654->base, PHY_CTRL4, ITAPDLYENA_MASK,
+			   1 << ITAPDLYENA_SHIFT);
+
+	for (itap = 0; itap < ITAP_MAX; itap++) {
+		sdhci_am654_write_itapdly(sdhci_am654, itap);
+
+		cur_val = !mmc_send_tuning(host->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;
+	sdhci_am654_write_itapdly(sdhci_am654, itap);
+
+	return 0;
+}
+
 static struct sdhci_ops sdhci_am654_ops = {
+	.platform_execute_tuning = sdhci_am654_platform_execute_tuning,
 	.get_max_clock = sdhci_pltfm_clk_get_max_clock,
 	.get_timeout_clock = sdhci_pltfm_clk_get_max_clock,
 	.set_uhs_signaling = sdhci_set_uhs_signaling,
@@ -426,6 +465,7 @@ static const struct sdhci_am654_driver_data sdhci_am654_drvdata = {
 };
 
 static struct sdhci_ops sdhci_j721e_8bit_ops = {
+	.platform_execute_tuning = sdhci_am654_platform_execute_tuning,
 	.get_max_clock = sdhci_pltfm_clk_get_max_clock,
 	.get_timeout_clock = sdhci_pltfm_clk_get_max_clock,
 	.set_uhs_signaling = sdhci_set_uhs_signaling,
@@ -449,6 +489,7 @@ static const struct sdhci_am654_driver_data sdhci_j721e_8bit_drvdata = {
 };
 
 static struct sdhci_ops sdhci_j721e_4bit_ops = {
+	.platform_execute_tuning = sdhci_am654_platform_execute_tuning,
 	.get_max_clock = sdhci_pltfm_clk_get_max_clock,
 	.get_timeout_clock = sdhci_pltfm_clk_get_max_clock,
 	.set_uhs_signaling = sdhci_set_uhs_signaling,
-- 
2.17.1