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

Kuan-Wei Chiu
2026-01-01T21:15:56Z

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@gmail.com>
Tested-by: Daniel Palmer <daniel@0x0f.com>
Reviewed-by: Yao Zi <me@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@gmail.com>
+S: Maintained
+F: drivers/timer/goldfish_timer.c
+F: include/goldfish_timer.h
+
I2C
M: Heiko Schocher <hs@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@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@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