1 files changed, 96 insertions, 0 deletions
diff --git a/arch/sh/boards/mach-dreamcast/rtc.c b/arch/sh/boards/mach-dreamcast/rtc.c
new file mode 100644
index 0000000000..7873cd27e4
--- /dev/null
+++ b/arch/sh/boards/mach-dreamcast/rtc.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * arch/sh/boards/dreamcast/rtc.c
+ *
+ * Dreamcast AICA RTC routines.
+ *
+ * Copyright (c) 2001, 2002 M. R. Brown <mrbrown@0xd6.org>
+ * Copyright (c) 2002 Paul Mundt <lethal@chaoticdreams.org>
+ */
+
+#include <linux/time.h>
+#include <linux/rtc.h>
+#include <linux/io.h>
+#include <linux/platform_device.h>
+
+/* The AICA RTC has an Epoch of 1/1/1950, so we must subtract 20 years (in
+   seconds) to get the standard Unix Epoch when getting the time, and add
+   20 years when setting the time. */
+#define TWENTY_YEARS ((20 * 365LU + 5) * 86400)
+
+/* The AICA RTC is represented by a 32-bit seconds counter stored in 2 16-bit
+   registers.*/
+#define AICA_RTC_SECS_H		0xa0710000
+#define AICA_RTC_SECS_L		0xa0710004
+
+/**
+ * aica_rtc_gettimeofday - Get the time from the AICA RTC
+ * @dev: the RTC device (ignored)
+ * @tm: pointer to resulting RTC time structure
+ *
+ * Grabs the current RTC seconds counter and adjusts it to the Unix Epoch.
+ */
+static int aica_rtc_gettimeofday(struct device *dev, struct rtc_time *tm)
+{
+	unsigned long val1, val2;
+	time64_t t;
+
+	do {
+		val1 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
+			(__raw_readl(AICA_RTC_SECS_L) & 0xffff);
+
+		val2 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
+			(__raw_readl(AICA_RTC_SECS_L) & 0xffff);
+	} while (val1 != val2);
+
+	/* normalize to 1970..2106 time range */
+	t = (u32)(val1 - TWENTY_YEARS);
+
+	rtc_time64_to_tm(t, tm);
+
+	return 0;
+}
+
+/**
+ * aica_rtc_settimeofday - Set the AICA RTC to the current time
+ * @dev: the RTC device (ignored)
+ * @tm: pointer to new RTC time structure
+ *
+ * Adjusts the given @tv to the AICA Epoch and sets the RTC seconds counter.
+ */
+static int aica_rtc_settimeofday(struct device *dev, struct rtc_time *tm)
+{
+	unsigned long val1, val2;
+	time64_t secs = rtc_tm_to_time64(tm);
+	u32 adj = secs + TWENTY_YEARS;
+
+	do {
+		__raw_writel((adj & 0xffff0000) >> 16, AICA_RTC_SECS_H);
+		__raw_writel((adj & 0xffff), AICA_RTC_SECS_L);
+
+		val1 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
+			(__raw_readl(AICA_RTC_SECS_L) & 0xffff);
+
+		val2 = ((__raw_readl(AICA_RTC_SECS_H) & 0xffff) << 16) |
+			(__raw_readl(AICA_RTC_SECS_L) & 0xffff);
+	} while (val1 != val2);
+
+	return 0;
+}
+
+static const struct rtc_class_ops rtc_generic_ops = {
+	.read_time = aica_rtc_gettimeofday,
+	.set_time = aica_rtc_settimeofday,
+};
+
+static int __init aica_time_init(void)
+{
+	struct platform_device *pdev;
+
+	pdev = platform_device_register_data(NULL, "rtc-generic", -1,
+					     &rtc_generic_ops,
+					     sizeof(rtc_generic_ops));
+
+	return PTR_ERR_OR_ZERO(pdev);
+}
+arch_initcall(aica_time_init);