[PATCH v4 1/6] serial: Add Goldfish TTY driver

Kuan-Wei Chiu
2026-01-01T21:15:47Z

Add support for the Google Goldfish TTY serial device. This virtual
device is commonly used in QEMU virtual machines (such as the m68k
virt machine) and Android emulators.

The driver implements basic console output and input polling using the
Goldfish MMIO interface.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Yao Zi <me@ziyao.cc>
Tested-by: Daniel Palmer <daniel@0x0f.com>
---
Changes in v4:
- Support DT probing with platform data as a fallback.

MAINTAINERS | 6 ++
drivers/serial/Kconfig | 8 +++
drivers/serial/Makefile | 1 +
drivers/serial/serial_goldfish.c | 109 +++++++++++++++++++++++++++++++
include/goldfish_tty.h | 18 +++++
5 files changed, 142 insertions(+)
create mode 100644 drivers/serial/serial_goldfish.c
create mode 100644 include/goldfish_tty.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 6ce0bbce13d..da4a6e4d518 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1259,6 +1259,12 @@ S: Maintained
F: drivers/misc/gsc.c
F: include/gsc.h

+GOLDFISH SERIAL DRIVER
+M: Kuan-Wei Chiu <visitorckw@gmail.com>
+S: Maintained
+F: drivers/serial/serial_goldfish.c
+F: include/goldfish_tty.h
+
I2C
M: Heiko Schocher <hs@nabladev.com>
S: Maintained
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 371d7aa5bba..b84cb9ec781 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -1193,4 +1193,12 @@ config SYS_SDMR
depends on MPC8XX_CONS
default 0x0

+config SERIAL_GOLDFISH
+ bool "Goldfish TTY support"
+ depends on DM_SERIAL
+ help
+ Select this to enable support for the Goldfish TTY serial port.
+ This virtual device is commonly used by QEMU virtual machines
+ (e.g. m68k virt) for console output.
+
endif
diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
index 8eaae62b0fc..fe8d23be512 100644
--- a/drivers/serial/Makefile
+++ b/drivers/serial/Makefile
@@ -63,3 +63,4 @@ obj-$(CONFIG_XTENSA_SEMIHOSTING_SERIAL) += serial_xtensa_semihosting.o
obj-$(CONFIG_S5P4418_PL011_SERIAL) += serial_s5p4418_pl011.o

obj-$(CONFIG_UART4_SERIAL) += serial_adi_uart4.o
+obj-$(CONFIG_SERIAL_GOLDFISH) += serial_goldfish.o
diff --git a/drivers/serial/serial_goldfish.c b/drivers/serial/serial_goldfish.c
new file mode 100644
index 00000000000..278d0cf3e0d
--- /dev/null
+++ b/drivers/serial/serial_goldfish.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
+ * Goldfish TTY driver for U-Boot
+ */
+
+#include <asm/io.h>
+#include <dm.h>
+#include <goldfish_tty.h>
+#include <linux/types.h>
+#include <mapmem.h>
+#include <serial.h>
+
+/* Goldfish TTY Register Offsets */
+#define GOLDFISH_TTY_PUT_CHAR 0x00
+#define GOLDFISH_TTY_BYTES_READY 0x04
+#define GOLDFISH_TTY_CMD 0x08
+#define GOLDFISH_TTY_DATA_PTR 0x10
+#define GOLDFISH_TTY_DATA_LEN 0x14
+#define GOLDFISH_TTY_DATA_PTR_HIGH 0x18
+#define GOLDFISH_TTY_VERSION 0x20
+
+/* Commands */
+#define CMD_WRITE_BUFFER 2
+#define CMD_READ_BUFFER 3
+
+struct goldfish_tty_priv {
+ void __iomem *base;
+ u8 rx_buf;
+};
+
+static int goldfish_serial_getc(struct udevice *dev)
+{
+ struct goldfish_tty_priv *priv = dev_get_priv(dev);
+ unsigned long paddr;
+ u32 count;
+
+ count = __raw_readl(priv->base + GOLDFISH_TTY_BYTES_READY);
+ if (count == 0)
+ return -EAGAIN;
+
+ paddr = virt_to_phys((void *)&priv->rx_buf);
+
+ __raw_writel(0, priv->base + GOLDFISH_TTY_DATA_PTR_HIGH);
+ __raw_writel(paddr, priv->base + GOLDFISH_TTY_DATA_PTR);
+ __raw_writel(1, priv->base + GOLDFISH_TTY_DATA_LEN);
+ __raw_writel(CMD_READ_BUFFER, priv->base + GOLDFISH_TTY_CMD);
+
+ return priv->rx_buf;
+}
+
+static int goldfish_serial_putc(struct udevice *dev, const char ch)
+{
+ struct goldfish_tty_priv *priv = dev_get_priv(dev);
+
+ __raw_writel(ch, priv->base + GOLDFISH_TTY_PUT_CHAR);
+
+ return 0;
+}
+
+static int goldfish_serial_pending(struct udevice *dev, bool input)
+{
+ struct goldfish_tty_priv *priv = dev_get_priv(dev);
+
+ if (input)
+ return __raw_readl(priv->base + GOLDFISH_TTY_BYTES_READY);
+
+ return 0;
+}
+
+static int goldfish_serial_probe(struct udevice *dev)
+{
+ struct goldfish_tty_priv *priv = dev_get_priv(dev);
+ struct goldfish_tty_plat *plat = dev_get_plat(dev);
+ fdt_addr_t addr;
+
+ addr = dev_read_addr(dev);
+ if (addr != FDT_ADDR_T_NONE) {
+ priv->base = map_sysmem(addr, 0x1000);
+ } else {
+ plat = dev_get_plat(dev);
+ if (!plat)
+ return -EINVAL;
+ priv->base = plat->base;
+ }
+
+ return 0;
+}
+
+static const struct dm_serial_ops goldfish_serial_ops = {
+ .putc = goldfish_serial_putc,
+ .pending = goldfish_serial_pending,
+ .getc = goldfish_serial_getc,
+};
+
+static const struct udevice_id goldfish_serial_ids[] = {
+ { .compatible = "google,goldfish-tty" },
+ { }
+};
+
+U_BOOT_DRIVER(serial_goldfish) = {
+ .name = "serial_goldfish",
+ .id = UCLASS_SERIAL,
+ .of_match = goldfish_serial_ids,
+ .probe = goldfish_serial_probe,
+ .ops = &goldfish_serial_ops,
+ .priv_auto = sizeof(struct goldfish_tty_priv),
+ .flags = DM_FLAG_PRE_RELOC,
+};
diff --git a/include/goldfish_tty.h b/include/goldfish_tty.h
new file mode 100644
index 00000000000..8777da4942d
--- /dev/null
+++ b/include/goldfish_tty.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2025, Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+#ifndef _GOLDFISH_TTY_H_
+#define _GOLDFISH_TTY_H_
+
+#include <linux/types.h>
+
+/* Platform data for the Goldfish TTY driver
+ * Used to pass hardware base address from Board to Driver
+ */
+struct goldfish_tty_plat {
+ void __iomem *base;
+};
+
+#endif /* _GOLDFISH_TTY_H_ */
--
2.52.0.358.g0dd7633a29-goog