timer: Add Goldfish timer driver

Add support for the Goldfish timer driver. This driver utilizes the
Goldfish RTC hardware to provide a nanosecond-resolution timer. This
virtual device is commonly found in QEMU virtual machines (such as the
m68k virt machine) and Android emulators.

The driver implements the standard U-Boot timer UCLASS interface,
exposing a 64-bit monotonically increasing counter with a 1GHz clock
rate derived from the RTC registers.

Signed-off-by: Kuan-Wei Chiu <[email protected]>
Tested-by: Daniel Palmer <[email protected]>
Reviewed-by: Yao Zi <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Reviewed-by: Angelo Dureghello <[email protected]>

1 files changed, 89 insertions, 0 deletions

diff --git a/drivers/timer/goldfish_timer.c b/drivers/timer/goldfish_timer.c
new file mode 100644
index 00000000000..70673bbd93c
--- /dev/null
+++ b/drivers/timer/goldfish_timer.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2025, Kuan-Wei Chiu <[email protected]>
+ *
+ * Goldfish Timer driver
+ */
+
+#include <dm.h>
+#include <goldfish_timer.h>
+#include <mapmem.h>
+#include <timer.h>
+#include <asm/io.h>
+#include <linux/errno.h>
+
+struct goldfish_timer_priv {
+	void __iomem *base;
+};
+
+/* Goldfish RTC registers used as Timer */
+#define TIMER_TIME_LOW	0x00
+#define TIMER_TIME_HIGH	0x04
+
+static u64 goldfish_timer_get_count(struct udevice *dev)
+{
+	struct goldfish_timer_priv *priv = dev_get_priv(dev);
+	u32 low, high;
+	u64 time;
+
+	/*
+	 * TIMER_TIME_HIGH is only updated when TIMER_TIME_LOW is read.
+	 * We must read LOW before HIGH to latch the high 32-bit value
+	 * and ensure a consistent 64-bit timestamp.
+	 */
+	low = readl(priv->base + TIMER_TIME_LOW);
+	high = readl(priv->base + TIMER_TIME_HIGH);
+
+	time = ((u64)high << 32) | low;
+
+	return time;
+}
+
+static int goldfish_timer_of_to_plat(struct udevice *dev)
+{
+	struct goldfish_timer_plat *plat = dev_get_plat(dev);
+	fdt_addr_t addr;
+
+	addr = dev_read_addr(dev);
+	if (addr != FDT_ADDR_T_NONE)
+		plat->reg = addr;
+
+	return 0;
+}
+
+static int goldfish_timer_probe(struct udevice *dev)
+{
+	struct goldfish_timer_plat *plat = dev_get_plat(dev);
+	struct goldfish_timer_priv *priv = dev_get_priv(dev);
+	struct timer_dev_priv *uc_priv = dev_get_uclass_priv(dev);
+
+	if (!plat->reg)
+		return -EINVAL;
+
+	priv->base = map_sysmem(plat->reg, 0x20);
+
+	/* Goldfish RTC counts in nanoseconds, so the rate is 1GHz */
+	uc_priv->clock_rate = 1000000000;
+
+	return 0;
+}
+
+static const struct timer_ops goldfish_timer_ops = {
+	.get_count = goldfish_timer_get_count,
+};
+
+static const struct udevice_id goldfish_timer_ids[] = {
+	{ .compatible = "google,goldfish-rtc" },
+	{ }
+};
+
+U_BOOT_DRIVER(goldfish_timer) = {
+	.name	= "goldfish_timer",
+	.id	= UCLASS_TIMER,
+	.of_match = goldfish_timer_ids,
+	.of_to_plat = goldfish_timer_of_to_plat,
+	.plat_auto  = sizeof(struct goldfish_timer_plat),
+	.ops	= &goldfish_timer_ops,
+	.probe	= goldfish_timer_probe,
+	.priv_auto = sizeof(struct goldfish_timer_priv),
+};