[1/3] rtc: Add support for the SSD20xD RTC

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 753872408615..894151163ab8 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -1978,4 +1978,15 @@  config RTC_DRV_POLARFIRE_SOC
 	  This driver can also be built as a module, if so, the module
 	  will be called "rtc-mpfs".
 
+config RTC_DRV_SSD20XD
+	tristate "SigmaStar SSD20XD RTC"
+	depends on ARCH_MSTARV7 || COMPILE_TEST
+	default ARCH_MSTARV7
+	help
+	  If you say yes here you get support for the SigmaStar SSD20XD On-Chip
+	  Real Time Clock.
+
+	  This driver can also be built as a module, if so, the module
+	  will be called "rtc-ssd20xd".
+
 endif # RTC_CLASS
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index ea445d1ebb17..f14fff00a7aa 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -103,6 +103,7 @@  obj-$(CONFIG_RTC_DRV_MESON)	+= rtc-meson.o
 obj-$(CONFIG_RTC_DRV_MOXART)	+= rtc-moxart.o
 obj-$(CONFIG_RTC_DRV_MPC5121)	+= rtc-mpc5121.o
 obj-$(CONFIG_RTC_DRV_MSC313)	+= rtc-msc313.o
+obj-$(CONFIG_RTC_DRV_SSD20XD) += rtc-ssd20xd.o
 obj-$(CONFIG_RTC_DRV_MSM6242)	+= rtc-msm6242.o
 obj-$(CONFIG_RTC_DRV_MT2712)	+= rtc-mt2712.o
 obj-$(CONFIG_RTC_DRV_MT6397)	+= rtc-mt6397.o
diff --git a/drivers/rtc/rtc-ssd20xd.c b/drivers/rtc/rtc-ssd20xd.c
new file mode 100644
index 000000000000..4dfa37109d88
--- /dev/null
+++ b/drivers/rtc/rtc-ssd20xd.c
@@ -0,0 +1,249 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Real time clocks driver for MStar/SigmaStar SSD20xD SoCs.
+ *
+ * (C) 2021 Daniel Palmer
+ * (C) 2023 Romain Perier
+ */
+
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/regmap.h>
+#include <linux/pm.h>
+
+#define REG_CTRL	0x0
+#define REG_CTRL1	0x4
+#define REG_ISO_CTRL	0xc
+#define REG_WRDATA_L	0x10
+#define REG_WRDATA_H	0x14
+#define REG_ISOACK	0x20
+#define REG_RDDATA_L	0x24
+#define REG_RDDATA_H	0x28
+#define REG_RDCNT_L	0x30
+#define REG_RDCNT_H	0x34
+#define REG_CNT_TRIG	0x38
+#define REG_PWRCTRL	0x3c
+#define REG_RTC_TEST	0x54
+
+#define CNT_RD_TRIG_BIT BIT(0)
+#define CNT_RD_BIT BIT(0)
+#define BASE_WR_BIT BIT(1)
+#define BASE_RD_BIT BIT(2)
+#define CNT_RST_BIT BIT(3)
+#define ISO_CTRL_ACK_MASK BIT(3)
+#define ISO_CTRL_ACK_SHIFT 3
+#define SW0_WR_BIT BIT(5)
+#define SW1_WR_BIT BIT(6)
+#define SW0_RD_BIT BIT(7)
+#define SW1_RD_BIT BIT(8)
+
+#define ISO_CTRL_MASK GENMASK(2, 0)
+
+struct ssd20xd_rtc {
+	struct rtc_device *rtc_dev;
+	void __iomem *base;
+};
+
+static u8 read_iso_en(void __iomem *base)
+{
+	return readb(base + REG_RTC_TEST) & 0x1;
+}
+
+static u8 read_iso_ctrl_ack(void __iomem *base)
+{
+	return (readb(base + REG_ISOACK) & ISO_CTRL_ACK_MASK) >> ISO_CTRL_ACK_SHIFT;
+}
+
+static int ssd20xd_rtc_isoctrl(struct ssd20xd_rtc *priv)
+{
+	static const unsigned int sequence[] = { 0x0, 0x1, 0x3, 0x7, 0x5, 0x1, 0x0 };
+	unsigned int val;
+	struct device *dev = &priv->rtc_dev->dev;
+	int i, ret;
+
+	/*
+	 * This gates iso_en by writing a special sequence of bytes to iso_ctrl
+	 * and ensuring that it has been correctly applied by reading iso_ctrl_ack
+	 */
+	for (i = 0; i < ARRAY_SIZE(sequence); i++) {
+		writeb(sequence[i] & ISO_CTRL_MASK, priv->base +  REG_ISO_CTRL);
+
+		ret = read_poll_timeout(read_iso_ctrl_ack, val, val == (i % 2), 100,
+					20 * 100, true, priv->base);
+		if (ret) {
+			dev_err(dev, "Timeout waiting for ack byte %i (%x) of sequence\n", i,
+				sequence[i]);
+			return ret;
+		}
+	}
+
+	/*
+	 * At this point iso_en should be raised for 1ms
+	 */
+	ret = read_poll_timeout(read_iso_en, val, val, 100, 22 * 100, true, priv->base);
+	if (ret)
+		dev_err(dev, "Timeout waiting for iso_en\n");
+	mdelay(2);
+	return 0;
+}
+
+static void ssd20xd_rtc_read_reg(struct ssd20xd_rtc *priv, unsigned int reg,
+				 unsigned int field, unsigned int *base)
+{
+	unsigned int l, h;
+	u16 val;
+
+	/* Ask for the content of an RTC value into RDDATA by gating iso_en,
+	 * then iso_en is gated and the content of RDDATA can be read
+	 */
+	val = readw(priv->base + reg);
+	writew(val | field, priv->base + reg);
+	ssd20xd_rtc_isoctrl(priv);
+	writew(val & ~field, priv->base + reg);
+
+	l = readw(priv->base + REG_RDDATA_L);
+	h = readw(priv->base + REG_RDDATA_H);
+
+	*base = (h << 16) | l;
+}
+
+static void ssd20xd_rtc_write_reg(struct ssd20xd_rtc *priv, unsigned int reg,
+				  unsigned int field, u32 base)
+{
+	u16 val;
+
+	/* Set the content of an RTC value from WRDATA by gating iso_en */
+	val = readw(priv->base + reg);
+	writew(val | field, priv->base + reg);
+	writew(base, priv->base + REG_WRDATA_L);
+	writew(base >> 16, priv->base + REG_WRDATA_H);
+	ssd20xd_rtc_isoctrl(priv);
+	writew(val & ~field, priv->base + reg);
+}
+
+static int ssd20xd_rtc_read_counter(struct ssd20xd_rtc *priv, unsigned int *counter)
+{
+	unsigned int l, h;
+	u16 val;
+
+	val = readw(priv->base + REG_CTRL1);
+	writew(val | CNT_RD_BIT, priv->base + REG_CTRL1);
+	ssd20xd_rtc_isoctrl(priv);
+	writew(val & ~CNT_RD_BIT, priv->base + REG_CTRL1);
+
+	val = readw(priv->base + REG_CTRL1);
+	writew(val | CNT_RD_TRIG_BIT, priv->base + REG_CNT_TRIG);
+	writew(val & ~CNT_RD_TRIG_BIT, priv->base + REG_CNT_TRIG);
+
+	l = readw(priv->base + REG_RDCNT_L);
+	h = readw(priv->base + REG_RDCNT_H);
+
+	*counter = (h << 16) | l;
+
+	return 0;
+}
+
+static int ssd20xd_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ssd20xd_rtc *priv = dev_get_drvdata(dev);
+	unsigned int sw0, base, counter;
+	u32 seconds;
+	int ret;
+
+	/* Check that RTC is enabled by SW */
+	ssd20xd_rtc_read_reg(priv, REG_CTRL, SW0_RD_BIT, &sw0);
+	if (sw0 != 1)
+		return -EINVAL;
+
+	/* Get RTC base value from RDDATA */
+	ssd20xd_rtc_read_reg(priv, REG_CTRL, BASE_RD_BIT, &base);
+	/* Get RTC counter value from RDDATA */
+	ret = ssd20xd_rtc_read_counter(priv, &counter);
+	if (ret)
+		return ret;
+
+	seconds = base + counter;
+
+	rtc_time64_to_tm(seconds, tm);
+
+	return 0;
+}
+
+static int ssd20xd_rtc_reset_counter(struct ssd20xd_rtc *priv)
+{
+	u16 val;
+
+	val = readw(priv->base + REG_CTRL);
+	writew(val | CNT_RST_BIT, priv->base + REG_CTRL);
+	ssd20xd_rtc_isoctrl(priv);
+	writew(val & ~CNT_RST_BIT, priv->base + REG_CTRL);
+	ssd20xd_rtc_isoctrl(priv);
+
+	return 0;
+}
+
+static int ssd20xd_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ssd20xd_rtc *priv = dev_get_drvdata(dev);
+	unsigned long seconds = rtc_tm_to_time64(tm);
+
+	ssd20xd_rtc_write_reg(priv, REG_CTRL, BASE_WR_BIT, seconds);
+	ssd20xd_rtc_reset_counter(priv);
+	ssd20xd_rtc_write_reg(priv, REG_CTRL, SW0_WR_BIT, 1);
+
+	return 0;
+}
+
+static const struct rtc_class_ops ssd20xd_rtc_ops = {
+	.read_time = ssd20xd_rtc_read_time,
+	.set_time = ssd20xd_rtc_set_time,
+};
+
+static int ssd20xd_rtc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct ssd20xd_rtc *priv;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(struct ssd20xd_rtc), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	priv->rtc_dev = devm_rtc_allocate_device(dev);
+	if (IS_ERR(priv->rtc_dev))
+		return PTR_ERR(priv->rtc_dev);
+
+	priv->rtc_dev->ops = &ssd20xd_rtc_ops;
+	priv->rtc_dev->range_max = U32_MAX;
+
+	platform_set_drvdata(pdev, priv);
+
+	return devm_rtc_register_device(priv->rtc_dev);
+}
+
+static const struct of_device_id ssd20xd_rtc_of_match_table[] = {
+	{ .compatible = "mstar,ssd20xd-rtc" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ssd20xd_rtc_of_match_table);
+
+static struct platform_driver ssd20xd_rtc_driver = {
+	.probe = ssd20xd_rtc_probe,
+	.driver = {
+		.name = "ssd20xd-rtc",
+		.of_match_table = ssd20xd_rtc_of_match_table,
+	},
+};
+module_platform_driver(ssd20xd_rtc_driver);
+
+MODULE_AUTHOR("Daniel Palmer <daniel@thingy.jp>");
+MODULE_AUTHOR("Romain Perier <romain.perier@gmail.com>");
+MODULE_DESCRIPTION("MStar SSD20xD RTC Driver");
+MODULE_LICENSE("GPL v2");