From 2d6dc19fd25d7ea1307951f45e4c372f1ff3daeb Mon Sep 17 00:00:00 2001
From: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Date: Sun, 31 Dec 2023 00:53:00 +0100
Subject: [PATCH] rtc: driver for Goldfish RTC

The Goldfish RTC is a virtual device which may be supplied by QEMU.
It is enabled by default on QEMU's RISC-V virt machine.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
---
 drivers/rtc/Kconfig        |   7 +++
 drivers/rtc/Makefile       |   1 +
 drivers/rtc/goldfish_rtc.c | 105 +++++++++++++++++++++++++++++++++++++
 3 files changed, 113 insertions(+)
 create mode 100644 drivers/rtc/goldfish_rtc.c

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 23173139e0..7fc53a6d61 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -122,6 +122,13 @@ config RTC_EMULATION
 	  CONFIG_BOOTP_NTPSERVER. The RTC time is advanced according to CPU
 	  ticks.
 
+config RTC_GOLDFISH
+	bool "Enable Goldfish driver"
+	depends on DM_RTC
+	help
+	  The Goldfish RTC is a virtual device which may be supplied by QEMU.
+	  It is enabled by default on QEMU's RISC-V virt machine.
+
 config RTC_ISL1208
 	bool "Enable ISL1208 driver"
 	depends on DM_RTC
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 308fab8da9..03a424c31a 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_RTC_DS1374) += ds1374.o
 obj-$(CONFIG_RTC_DS3231) += ds3231.o
 obj-$(CONFIG_RTC_DS3232) += ds3232.o
 obj-$(CONFIG_RTC_EMULATION) += emul_rtc.o
+obj-$(CONFIG_RTC_GOLDFISH) += goldfish_rtc.o
 obj-$(CONFIG_RTC_HT1380) += ht1380.o
 obj-$(CONFIG_$(SPL_TPL_)RTC_SANDBOX) += i2c_rtc_emul.o
 obj-$(CONFIG_RTC_ISL1208) += isl1208.o
diff --git a/drivers/rtc/goldfish_rtc.c b/drivers/rtc/goldfish_rtc.c
new file mode 100644
index 0000000000..1ace990385
--- /dev/null
+++ b/drivers/rtc/goldfish_rtc.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright 2023, Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
+ *
+ * This driver emulates a real time clock based on timer ticks.
+ */
+
+#include <div64.h>
+#include <dm.h>
+#include <mapmem.h>
+#include <rtc.h>
+#include <linux/io.h>
+
+/**
+ * struct goldfish_rtc - private data for RTC driver
+ */
+struct goldfish_rtc {
+	/**
+	 * @base: base address for register file
+	 */
+	void __iomem *base;
+	/**
+	 * @isdst: daylight saving time
+	 */
+	int isdst;
+};
+
+/* Register offsets */
+#define GOLDFISH_TIME_LOW	0x00
+#define GOLDFISH_TIME_HIGH	0x04
+
+static int goldfish_rtc_get(struct udevice *dev, struct rtc_time *time)
+{
+	struct goldfish_rtc *priv = dev_get_priv(dev);
+	void __iomem *base = priv->base;
+	u64 time_high;
+	u64 time_low;
+	u64 now;
+
+	time_low = ioread32(base + GOLDFISH_TIME_LOW);
+	time_high = ioread32(base + GOLDFISH_TIME_HIGH);
+	now = (time_high << 32) | time_low;
+
+	do_div(now, 1000000000U);
+
+	rtc_to_tm(now, time);
+	time->tm_isdst = priv->isdst;
+
+	return 0;
+}
+
+static int goldfish_rtc_set(struct udevice *dev, const struct rtc_time *time)
+{
+	struct goldfish_rtc *priv = dev_get_priv(dev);
+	void __iomem *base = priv->base;
+	u64 now;
+
+	if (time->tm_year < 1970)
+		return -EINVAL;
+
+	now = rtc_mktime(time) * 1000000000ULL;
+	iowrite32(now >> 32, base + GOLDFISH_TIME_HIGH);
+	iowrite32(now, base + GOLDFISH_TIME_LOW);
+
+	if (time->tm_isdst > 0)
+		priv->isdst = 1;
+	else if (time->tm_isdst < 0)
+		priv->isdst = -1;
+	else
+		priv->isdst = 0;
+
+	return 0;
+}
+
+int goldfish_rtc_probe(struct udevice *dev)
+{
+	struct goldfish_rtc *priv = dev_get_priv(dev);
+	fdt_addr_t addr;
+
+	addr = dev_read_addr(dev);
+	if (addr == FDT_ADDR_T_NONE)
+		return -EINVAL;
+	priv->base = map_sysmem(addr, 0x20);
+
+	return 0;
+}
+
+static const struct rtc_ops goldfish_rtc_ops = {
+	.get = goldfish_rtc_get,
+	.set = goldfish_rtc_set,
+};
+
+static const struct udevice_id goldfish_rtc_of_match[] = {
+	{ .compatible = "google,goldfish-rtc", },
+	{},
+};
+
+U_BOOT_DRIVER(rtc_goldfish) = {
+	.name		= "rtc_goldfish",
+	.id		= UCLASS_RTC,
+	.ops		= &goldfish_rtc_ops,
+	.probe		= goldfish_rtc_probe,
+	.of_match	= goldfish_rtc_of_match,
+	.priv_auto	= sizeof(struct goldfish_rtc),
+};
-- 
2.39.5