rtc: add ht1380 driver

Support Holtek HT1380/HT1381 Serial Timekeeper Chip. It provides seconds
, minutes, hours, day of the week, date, month and year information.

Datasheet:
https://www.holtek.com.tw/documents/10179/11842/ht1380_1v130.pdf

Signed-off-by: Sergei Antonov <saproj@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

configs/sandbox_defconfig

@@ -334,3 +334,4 @@ CONFIG_UNIT_TEST=y
 CONFIG_UT_TIME=y
 CONFIG_UT_DM=y
 CONFIG_IPV6=y
+CONFIG_RTC_HT1380=y

drivers/rtc/Kconfig

@@ -260,4 +260,13 @@ config RTC_ZYNQMP
 	  Say "yes" here to support the on chip real time clock
 	  present on Xilinx ZynqMP SoC.
 
+config RTC_HT1380
+	bool "Enable Holtek HT1380/HT1381 RTC driver"
+	depends on DM_RTC && DM_GPIO
+	help
+	  Say "yes" here to get support for Holtek HT1380/HT1381
+	  Serial Timekeeper IC which provides seconds, minutes, hours,
+	  day of the week, date, month and year information. It is to be
+	  connected via 3 GPIO pins which work as reset, clock, and data.
+
 endmenu

drivers/rtc/Makefile

@@ -21,6 +21,7 @@ obj-$(CONFIG_RTC_DS3231) += ds3231.o
 obj-$(CONFIG_RTC_DS3232) += ds3232.o
 obj-$(CONFIG_RTC_EMULATION) += emul_rtc.o
 obj-$(CONFIG_RTC_FTRTC010) += ftrtc010.o
+obj-$(CONFIG_RTC_HT1380) += ht1380.o
 obj-$(CONFIG_SANDBOX) += i2c_rtc_emul.o
 obj-$(CONFIG_RTC_IMXDI) += imxdi.o
 obj-$(CONFIG_RTC_ISL1208) += isl1208.o

drivers/rtc/ht1380.c

@@ -0,0 +1,329 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Holtek HT1380/HT1381 Serial Timekeeper Chip
+ *
+ * Communication with the chip is vendor-specific.
+ * It is done via 3 GPIO pins: reset, clock, and data.
+ * Describe in .dts this way:
+ *
+ * rtc {
+ *         compatible = "holtek,ht1380";
+ *         rst-gpios = <&gpio 19 GPIO_ACTIVE_LOW>;
+ *         clk-gpios = <&gpio 20 GPIO_ACTIVE_HIGH>;
+ *         dat-gpios = <&gpio 21 GPIO_ACTIVE_HIGH>;
+ * };
+ *
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <rtc.h>
+#include <bcd.h>
+#include <asm/gpio.h>
+#include <linux/delay.h>
+
+struct ht1380_priv {
+	struct gpio_desc rst_desc;
+	struct gpio_desc clk_desc;
+	struct gpio_desc dat_desc;
+};
+
+enum registers {
+	SEC,
+	MIN,
+	HOUR,
+	MDAY,
+	MONTH,
+	WDAY,
+	YEAR,
+	WP,
+	N_REGS
+};
+
+enum hour_mode {
+	AMPM_MODE = 0x80, /* RTC is in AM/PM mode */
+	PM_NOW = 0x20,    /* set if PM, clear if AM */
+};
+
+static const int BURST = 0xbe;
+static const int READ = 1;
+
+static void ht1380_half_period_delay(void)
+{
+	/*
+	 * Delay for half a period. 1 us complies with the 500 KHz maximum
+	 * input serial clock limit given by the datasheet.
+	 */
+	udelay(1);
+}
+
+static int ht1380_send_byte(struct ht1380_priv *priv, int byte)
+{
+	int ret;
+
+	for (int bit = 0; bit < 8; bit++) {
+		ret = dm_gpio_set_value(&priv->dat_desc, byte >> bit & 1);
+		if (ret)
+			break;
+		ht1380_half_period_delay();
+
+		ret = dm_gpio_set_value(&priv->clk_desc, 1);
+		if (ret)
+			break;
+		ht1380_half_period_delay();
+
+		ret = dm_gpio_set_value(&priv->clk_desc, 0);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
+/*
+ * Leave reset state. The transfer operation can then be started.
+ */
+static int ht1380_reset_off(struct ht1380_priv *priv)
+{
+	const unsigned int T_CC = 4; /* us, Reset to Clock Setup */
+	int ret;
+
+	/*
+	 * Leave RESET state.
+	 * Make sure we make the minimal delay required by the datasheet.
+	 */
+	ret = dm_gpio_set_value(&priv->rst_desc, 0);
+	udelay(T_CC);
+
+	return ret;
+}
+
+/*
+ * Enter reset state. Completes the transfer operation.
+ */
+static int ht1380_reset_on(struct ht1380_priv *priv)
+{
+	const unsigned int T_CWH = 4; /* us, Reset Inactive Time */
+	int ret;
+
+	/*
+	 * Enter RESET state.
+	 * Make sure we make the minimal delay required by the datasheet.
+	 */
+	ret = dm_gpio_set_value(&priv->rst_desc, 1);
+	udelay(T_CWH);
+
+	return ret;
+}
+
+static int ht1380_rtc_get(struct udevice *dev, struct rtc_time *tm)
+{
+	struct ht1380_priv *priv = dev_get_priv(dev);
+	int ret, i, bit, reg[N_REGS];
+
+	ret = dm_gpio_set_value(&priv->clk_desc, 0);
+	if (ret)
+		return ret;
+
+	ret = dm_gpio_set_dir_flags(&priv->dat_desc, GPIOD_IS_OUT);
+	if (ret)
+		return ret;
+
+	ret = ht1380_reset_off(priv);
+	if (ret)
+		goto exit;
+
+	ret = ht1380_send_byte(priv, BURST + READ);
+	if (ret)
+		goto exit;
+
+	ret = dm_gpio_set_dir_flags(&priv->dat_desc, GPIOD_IS_IN);
+	if (ret)
+		goto exit;
+
+	for (i = 0; i < N_REGS; i++) {
+		reg[i] = 0;
+
+		for (bit = 0; bit < 8; bit++) {
+			ht1380_half_period_delay();
+
+			ret = dm_gpio_set_value(&priv->clk_desc, 1);
+			if (ret)
+				goto exit;
+			ht1380_half_period_delay();
+
+			reg[i] |= dm_gpio_get_value(&priv->dat_desc) << bit;
+			ret = dm_gpio_set_value(&priv->clk_desc, 0);
+			if (ret)
+				goto exit;
+		}
+	}
+
+	ret = -EINVAL;
+
+	/* Correctness check: some bits are always zero */
+	if (reg[MIN] & 0x80 || reg[HOUR] & 0x40 || reg[MDAY] & 0xc0 ||
+	    reg[MONTH] & 0xe0 || reg[WDAY] & 0xf8 || reg[WP] & 0x7f)
+		goto exit;
+
+	/* Correctness check: some registers are always non-zero */
+	if (!reg[MDAY] || !reg[MONTH] || !reg[WDAY])
+		goto exit;
+
+	tm->tm_sec = bcd2bin(reg[SEC]);
+	tm->tm_min = bcd2bin(reg[MIN]);
+	if (reg[HOUR] & AMPM_MODE) {
+		/* AM-PM Mode, range is 01-12 */
+		tm->tm_hour = bcd2bin(reg[HOUR] & 0x1f) % 12;
+		if (reg[HOUR] & PM_NOW) {
+			/* it is PM (otherwise AM) */
+			tm->tm_hour += 12;
+		}
+	} else {
+		/* 24-hour Mode, range is 0-23 */
+		tm->tm_hour = bcd2bin(reg[HOUR]);
+	}
+	tm->tm_mday = bcd2bin(reg[MDAY]);
+	tm->tm_mon = bcd2bin(reg[MONTH]);
+	tm->tm_year = 2000 + bcd2bin(reg[YEAR]);
+	tm->tm_wday = bcd2bin(reg[WDAY]) - 1;
+	tm->tm_yday = 0;
+	tm->tm_isdst = 0;
+
+	ret = 0;
+
+exit:
+	ht1380_reset_on(priv);
+
+	return ret;
+}
+
+static int ht1380_write_protection_off(struct ht1380_priv *priv)
+{
+	int ret;
+	const int PROTECT = 0x8e;
+
+	ret = ht1380_reset_off(priv);
+	if (ret)
+		return ret;
+
+	ret = ht1380_send_byte(priv, PROTECT);
+	if (ret)
+		return ret;
+	ret = ht1380_send_byte(priv, 0); /* WP bit is 0 */
+	if (ret)
+		return ret;
+
+	return ht1380_reset_on(priv);
+}
+
+static int ht1380_rtc_set(struct udevice *dev, const struct rtc_time *tm)
+{
+	struct ht1380_priv *priv = dev_get_priv(dev);
+	int ret, i, reg[N_REGS];
+
+	ret = dm_gpio_set_value(&priv->clk_desc, 0);
+	if (ret)
+		return ret;
+
+	ret = dm_gpio_set_dir_flags(&priv->dat_desc, GPIOD_IS_OUT);
+	if (ret)
+		goto exit;
+
+	ret = ht1380_write_protection_off(priv);
+	if (ret)
+		goto exit;
+
+	reg[SEC] = bin2bcd(tm->tm_sec);
+	reg[MIN] = bin2bcd(tm->tm_min);
+	reg[HOUR] = bin2bcd(tm->tm_hour);
+	reg[MDAY] = bin2bcd(tm->tm_mday);
+	reg[MONTH] = bin2bcd(tm->tm_mon);
+	reg[WDAY] = bin2bcd(tm->tm_wday) + 1;
+	reg[YEAR] = bin2bcd(tm->tm_year - 2000);
+	reg[WP] = 0x80; /* WP bit is 1 */
+
+	ret = ht1380_reset_off(priv);
+	if (ret)
+		goto exit;
+
+	ret = ht1380_send_byte(priv, BURST);
+	for (i = 0; i < N_REGS && ret; i++)
+		ret = ht1380_send_byte(priv, reg[i]);
+
+exit:
+	ht1380_reset_on(priv);
+
+	return ret;
+}
+
+static int ht1380_probe(struct udevice *dev)
+{
+	int ret;
+	struct ht1380_priv *priv;
+
+	priv = dev_get_priv(dev);
+	if (!priv)
+		return -EINVAL;
+
+	ret = gpio_request_by_name(dev, "rst-gpios", 0,
+				   &priv->rst_desc, GPIOD_IS_OUT);
+	if (ret)
+		goto fail_rst;
+
+	ret = gpio_request_by_name(dev, "clk-gpios", 0,
+				   &priv->clk_desc, GPIOD_IS_OUT);
+	if (ret)
+		goto fail_clk;
+
+	ret = gpio_request_by_name(dev, "dat-gpios", 0,
+				   &priv->dat_desc, 0);
+	if (ret)
+		goto fail_dat;
+
+	ret = ht1380_reset_on(priv);
+	if (ret)
+		goto fail;
+
+	return 0;
+
+fail:
+	dm_gpio_free(dev, &priv->dat_desc);
+fail_dat:
+	dm_gpio_free(dev, &priv->clk_desc);
+fail_clk:
+	dm_gpio_free(dev, &priv->rst_desc);
+fail_rst:
+	return ret;
+}
+
+static int ht1380_remove(struct udevice *dev)
+{
+	struct ht1380_priv *priv = dev_get_priv(dev);
+
+	dm_gpio_free(dev, &priv->rst_desc);
+	dm_gpio_free(dev, &priv->clk_desc);
+	dm_gpio_free(dev, &priv->dat_desc);
+
+	return 0;
+}
+
+static const struct rtc_ops ht1380_rtc_ops = {
+	.get = ht1380_rtc_get,
+	.set = ht1380_rtc_set,
+};
+
+static const struct udevice_id ht1380_rtc_ids[] = {
+	{ .compatible = "holtek,ht1380" },
+	{ }
+};
+
+U_BOOT_DRIVER(rtc_ht1380) = {
+	.name = "rtc-ht1380",
+	.id = UCLASS_RTC,
+	.probe = ht1380_probe,
+	.remove = ht1380_remove,
+	.of_match = ht1380_rtc_ids,
+	.ops = &ht1380_rtc_ops,
+	.priv_auto = sizeof(struct ht1380_priv),
+};