On Thu, Dec 18, 2025 at 06:52:50PM +0000, 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 <[email protected]> > --- > MAINTAINERS | 6 ++ > drivers/serial/Kconfig | 8 +++ > drivers/serial/Makefile | 1 + > drivers/serial/serial_goldfish.c | 112 +++++++++++++++++++++++++++++++ > include/goldfish_tty.h | 18 +++++ > 5 files changed, 145 insertions(+) > create mode 100644 drivers/serial/serial_goldfish.c > create mode 100644 include/goldfish_tty.h
... > diff --git a/drivers/serial/serial_goldfish.c > b/drivers/serial/serial_goldfish.c > new file mode 100644 > index 00000000000..85d2a93b6ff > --- /dev/null > +++ b/drivers/serial/serial_goldfish.c > @@ -0,0 +1,112 @@ > +// SPDX-License-Identifier: GPL-2.0+ GPL-2.0+ has been deprecated as a SPDX license identifier. GPL-2.0-or-later should probably be used instead[1]. > +/* > + * Copyright (C) 2025, Kuan-Wei Chiu <[email protected]> > + * Goldfish TTY driver for U-Boot > + */ > + > +#include <dm.h> > +#include <serial.h> > +#include <goldfish_tty.h> > +#include <asm/io.h> > +#include <linux/types.h> It looks better if you sort the headers :) ... > +static int goldfish_serial_getc(struct udevice *dev) > +{ > + static u8 rx_buf[4]; > + struct goldfish_tty_priv *priv = dev_get_priv(dev); > + unsigned long base = (unsigned long)priv->base; > + unsigned long paddr; > + u32 count; > + > + count = __raw_readl((void *)(base + GOLDFISH_TTY_BYTES_READY)); > + if (count == 0) > + return -EAGAIN; > + > + if (count > sizeof(rx_buf)) > + count = sizeof(rx_buf); > + > + paddr = virt_to_phys((void *)rx_buf); > + > + rx_buf[0] = 0xAA; > + > + __raw_writel(0, (void *)(base + GOLDFISH_TTY_DATA_PTR_HIGH)); > + __raw_writel(paddr, (void *)(base + GOLDFISH_TTY_DATA_PTR)); > + __raw_writel(count, (void *)(base + GOLDFISH_TTY_DATA_LEN)); You send a command that reads count bytes, where count represents the maximum of bytes available in the buffer and sizeof(rx_buf), so it's possible to read more than one character... > + __raw_writel(CMD_READ_BUFFER, (void *)(base + GOLDFISH_TTY_CMD)); > + > + if (rx_buf[0] == 0xAA) > + return -EAGAIN; > + > + return rx_buf[0]; But only the first character in the buffer is finally returned. Isn't the following characters (if present) are incorrectly discarded? rx_buf is declared as static in this case. Are you originally intended to do some type of buffering here? Additionally, I don't get the point of setting rx_buf[0] to 0xaa then checks whether it changes after sending CMD_READ_BUFFER. Is there a case that CMD_READ_BUFFER would fail even when reading TTY_BYTES_READY returns non-zero? I had a brief look at qemu's goldfish tty implementation, but didn't find such situation. > +} Best regards, Yao Zi [1]: https://lore.kernel.org/u-boot/20251212142859.GQ303283@bill-the-cat
