[PATCH 1/2] mmc: stm32_sdmmc2: Add support for probing bus voltage level translator

[Marek Vasut]

Add support for testing whether bus voltage level translator is present
and operational. This is useful on systems where the bus voltage level
translator is optional, as the translator can be auto-detected by the
driver and the feedback clock functionality can be disabled if it is
not present.

The translator test sets CMD high to avoid interfering with a card, and
then verifies whether signal set on CK is detected on CKIN. If the signal
is detected, translator is present, otherwise the CKIN feedback clock are
disabled.

Signed-off-by: Marek Vasut <marex at denx.de>
Cc: Patrice Chotard <patrice.chotard at foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay at foss.st.com>
---
 drivers/mmc/stm32_sdmmc2.c | 63 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 62 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/stm32_sdmmc2.c b/drivers/mmc/stm32_sdmmc2.c
index a3cdf7bcd9f..44bfc911af2 100644
--- a/drivers/mmc/stm32_sdmmc2.c
+++ b/drivers/mmc/stm32_sdmmc2.c
@@ -16,6 +16,7 @@
 #include <asm/bitops.h>
 #include <asm/cache.h>
 #include <dm/device_compat.h>
+#include <dm/pinctrl.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/libfdt.h>
@@ -645,6 +646,66 @@ static const struct dm_mmc_ops stm32_sdmmc2_ops = {
 	.host_power_cycle = stm32_sdmmc2_host_power_cycle,
 };
 
+static int stm32_sdmmc2_probe_level_translator(struct udevice *dev)
+{
+	struct stm32_sdmmc2_priv *priv = dev_get_priv(dev);
+	struct gpio_desc cmd_gpio;
+	struct gpio_desc ck_gpio;
+	struct gpio_desc ckin_gpio;
+	int clk_hi, clk_lo, ret;
+
+	/*
+	 * Assume the level translator is present if st,use-ckin is set.
+	 * This is to cater for DTs which do not implement this test.
+	 */
+	priv->clk_reg_msk |= SDMMC_CLKCR_SELCLKRX_CKIN;
+
+	ret = gpio_request_by_name(dev, "st,cmd-gpios", 0, &cmd_gpio,
+				   GPIOD_IS_OUT | GPIOD_IS_OUT_ACTIVE);
+	if (ret)
+		goto exit_cmd;
+
+	ret = gpio_request_by_name(dev, "st,ck-gpios", 0, &ck_gpio,
+				   GPIOD_IS_OUT | GPIOD_IS_OUT_ACTIVE);
+	if (ret)
+		goto exit_ck;
+
+	ret = gpio_request_by_name(dev, "st,ckin-gpios", 0, &ckin_gpio,
+				   GPIOD_IS_IN);
+	if (ret)
+		goto exit_ckin;
+
+	/* All GPIOs are valid, test whether level translator works */
+
+	/* Sample CKIN */
+	clk_hi = !!dm_gpio_get_value(&ckin_gpio);
+
+	/* Set CK low */
+	dm_gpio_set_value(&ck_gpio, 0);
+
+	/* Sample CKIN */
+	clk_lo = !!dm_gpio_get_value(&ckin_gpio);
+
+	/* Tristate all */
+	dm_gpio_set_dir_flags(&cmd_gpio, GPIOD_IS_IN);
+	dm_gpio_set_dir_flags(&ck_gpio, GPIOD_IS_IN);
+
+	/* Level translator is present if CK signal is propagated to CKIN */
+	if (!clk_hi || clk_lo)
+		priv->clk_reg_msk &= ~SDMMC_CLKCR_SELCLKRX_CKIN;
+
+	dm_gpio_free(dev, &ckin_gpio);
+
+exit_ckin:
+	dm_gpio_free(dev, &ck_gpio);
+exit_ck:
+	dm_gpio_free(dev, &cmd_gpio);
+exit_cmd:
+	pinctrl_select_state(dev, "default");
+
+	return 0;
+}
+
 static int stm32_sdmmc2_probe(struct udevice *dev)
 {
 	struct mmc_uclass_priv *upriv = dev_get_uclass_priv(dev);
@@ -662,7 +723,7 @@ static int stm32_sdmmc2_probe(struct udevice *dev)
 	if (dev_read_bool(dev, "st,sig-dir"))
 		priv->pwr_reg_msk |= SDMMC_POWER_DIRPOL;
 	if (dev_read_bool(dev, "st,use-ckin"))
-		priv->clk_reg_msk |= SDMMC_CLKCR_SELCLKRX_CKIN;
+		stm32_sdmmc2_probe_level_translator(dev);
 
 	ret = clk_get_by_index(dev, 0, &priv->clk);
 	if (ret)
-- 
2.33.0