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

[Romain Perier]

Newer SigmaStar SSD20xD SoCs contain a really low power RTC (300uA claimed),
capable of running while the system is sleeping (battery powered), this
is not the case with the other RTC on older SoCs. This adds basic support
for this RTC block.

Signed-off-by: Romain Perier <romain.perier@xxxxxxxxx>
Co-developed-by: Daniel Palmer <daniel@xxxxxxxx>
Signed-off-by: Daniel Palmer <daniel@xxxxxxxx>
---
 drivers/rtc/Kconfig       |  11 ++
 drivers/rtc/Makefile      |   1 +
 drivers/rtc/rtc-ssd20xd.c | 249 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 261 insertions(+)
 create mode 100644 drivers/rtc/rtc-ssd20xd.c

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@xxxxxxxxx>");
+MODULE_AUTHOR("Romain Perier <romain.perier@xxxxxxxxx>");
+MODULE_DESCRIPTION("MStar SSD20xD RTC Driver");
+MODULE_LICENSE("GPL v2");
-- 
2.39.2