[PATCH v5 1/7] serial: Add Goldfish TTY driver
Simon Glass
sjg at chromium.org
Tue Jan 6 00:30:28 CET 2026
Hi Kuan-Wei,
On Mon, 5 Jan 2026 at 11:21, Kuan-Wei Chiu <visitorckw at gmail.com> wrote:
>
> 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 at gmail.com>
> Reviewed-by: Yao Zi <me at ziyao.cc>
> Tested-by: Daniel Palmer <daniel at 0x0f.com>
> Acked-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> ---
> Changes in v5:
> - Rebase on u-boot/next branch.
>
> 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
>
Reviewed-by: Simon Glass <simon.glass at canonical.com>
One thought below.
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 27ce73d83f4..8f884ff495a 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1260,6 +1260,12 @@ S: Maintained
> F: drivers/misc/gsc.c
> F: include/gsc.h
>
> +GOLDFISH SERIAL DRIVER
> +M: Kuan-Wei Chiu <visitorckw at gmail.com>
> +S: Maintained
> +F: drivers/serial/serial_goldfish.c
> +F: include/goldfish_tty.h
> +
> INTERCONNECT:
> M: Neil Armstrong <neil.armstrong at linaro.org>
> 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 at 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;
> +}
Strictly speaking, reading the devicetree should be done in the
of_to_plat() method. So you would read the base address there.
Then probe() would convert that to a pointer (I suggest the same 'reg'
for registers, but it isn't that important).
> +
> +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 at 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
>
Regards,
Simon
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