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

[Heinrich Schuchardt <heinrich.schuchardt@canonical.com>]

On 1/1/26 18:54, Kuan-Wei Chiu 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@gmail.com>
> Reviewed-by: Yao Zi <me@ziyao.cc>
> Tested-by: Daniel Palmer <daniel@0x0f.com>

Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.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_ */