[PATCH v4 2/6] timer: Add Goldfish timer driver

[Kuan-Wei Chiu]

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 <visitorckw at gmail.com>
Tested-by: Daniel Palmer <daniel at 0x0f.com>
Reviewed-by: Yao Zi <me at ziyao.cc>
---
Changes in v4:
- Sort headers alphabetically.
- Add comment explaining read latching behavior.
- Support DT probing with platform data as a fallback.

 MAINTAINERS                    |  6 +++
 drivers/timer/Kconfig          |  8 ++++
 drivers/timer/Makefile         |  1 +
 drivers/timer/goldfish_timer.c | 81 ++++++++++++++++++++++++++++++++++
 include/goldfish_timer.h       | 13 ++++++
 5 files changed, 109 insertions(+)
 create mode 100644 drivers/timer/goldfish_timer.c
 create mode 100644 include/goldfish_timer.h

diff --git a/MAINTAINERS b/MAINTAINERS
index da4a6e4d518..fcc437a53ce 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1265,6 +1265,12 @@ S:	Maintained
 F:	drivers/serial/serial_goldfish.c
 F:	include/goldfish_tty.h
 
+GOLDFISH TIMER DRIVER
+M:	Kuan-Wei Chiu <visitorckw at gmail.com>
+S:	Maintained
+F:	drivers/timer/goldfish_timer.c
+F:	include/goldfish_timer.h
+
 I2C
 M:	Heiko Schocher <hs at nabladev.com>
 S:	Maintained
diff --git a/drivers/timer/Kconfig b/drivers/timer/Kconfig
index f9511503b02..a84a0dc0539 100644
--- a/drivers/timer/Kconfig
+++ b/drivers/timer/Kconfig
@@ -340,4 +340,12 @@ config STARFIVE_TIMER
 	  Select this to enable support for the timer found on
 	  Starfive SoC.
 
+config GOLDFISH_TIMER
+	bool "Goldfish Timer support"
+	depends on TIMER
+	help
+	  Select this to enable support for the Goldfish Timer.
+	  It uses the Goldfish RTC hardware to provide a nanosecond-resolution
+	  timer, commonly found in QEMU virt machines.
+
 endmenu
diff --git a/drivers/timer/Makefile b/drivers/timer/Makefile
index a72e411fb2f..d8b3f2b65d4 100644
--- a/drivers/timer/Makefile
+++ b/drivers/timer/Makefile
@@ -36,3 +36,4 @@ obj-$(CONFIG_MCHP_PIT64B_TIMER)	+= mchp-pit64b-timer.o
 obj-$(CONFIG_IMX_GPT_TIMER)	+= imx-gpt-timer.o
 obj-$(CONFIG_XILINX_TIMER)	+= xilinx-timer.o
 obj-$(CONFIG_STARFIVE_TIMER)	+= starfive-timer.o
+obj-$(CONFIG_GOLDFISH_TIMER)	+= goldfish_timer.o
diff --git a/drivers/timer/goldfish_timer.c b/drivers/timer/goldfish_timer.c
new file mode 100644
index 00000000000..63946b9ed97
--- /dev/null
+++ b/drivers/timer/goldfish_timer.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw at gmail.com>
+ *
+ * Goldfish Timer driver
+ */
+
+#include <asm/io.h>
+#include <dm.h>
+#include <goldfish_timer.h>
+#include <linux/errno.h>
+#include <mapmem.h>
+#include <timer.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_probe(struct udevice *dev)
+{
+	struct goldfish_timer_priv *priv = dev_get_priv(dev);
+	struct timer_dev_priv *uc_priv = dev_get_uclass_priv(dev);
+	struct goldfish_timer_plat *plat;
+	fdt_addr_t addr;
+
+	addr = dev_read_addr(dev);
+	if (addr != FDT_ADDR_T_NONE) {
+		priv->base = map_sysmem(addr, 0x20);
+	} else {
+		plat = dev_get_plat(dev);
+		if (!plat)
+			return -EINVAL;
+		priv->base = plat->base;
+	}
+
+	/* 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,
+	.ops	= &goldfish_timer_ops,
+	.probe	= goldfish_timer_probe,
+	.priv_auto = sizeof(struct goldfish_timer_priv),
+};
diff --git a/include/goldfish_timer.h b/include/goldfish_timer.h
new file mode 100644
index 00000000000..2ea28170759
--- /dev/null
+++ b/include/goldfish_timer.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw at gmail.com>
+ */
+
+#ifndef _GOLDFISH_TIMER_H_
+#define _GOLDFISH_TIMER_H_
+
+struct goldfish_timer_plat {
+	void __iomem *base;
+};
+
+#endif /* _GOLDFISH_TIMER_H_ */
-- 
2.52.0.358.g0dd7633a29-goog