Re: [PATCH 1/2] tty: serial: remove hub6 multiport support
From: Frank Li
Date: Fri Oct 16 2026 - 14:30:50 EST
On Fri, Oct 16, 2026 at 02:59:47PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> hub6 support was added in linux-0.99 and the hardware was already old at
> the time, being discontinued in 1990. The code for it has always been a
> mess since it adds another dimension to the I/O addressing in the driver
> that has leaked into many individual files.
>
> Hugo and Uwe have attempted several times this year alone to isolate
> the hub6 handling into the 8250_hub6.c file, but I feel that none of
> this has been a real improvement over the original standalone loadable
> module support.
>
> Any machine that would have used this ISA card in practice is likely
> 30 to 40 years old, and with i486 support now removed, it is clearly
> safe to just kill this all off. The only bit that has to remain
> is the ioctl interface, to ensure the serial_struct field is always
> zero.
>
> Link: https://mirrors.nycbug.org/pub/The_Unix_Archive/Unix_Usenet/comp.unix.sysv386/1990-December/007174.html
> Fixes: a300273c458c ("serial: 8250: hub6: Add cleanup code")
> Fixes: c526404a4a92 ("serial: 8250: Fix corner case for port matching")
> Fixes: 7ab80d1e7243 ("serial: 8250: fix compile error with hub6_match_port() when compiled as a module")
> Fixes: da7b5fd4e17f ("serial: 8250_hub6: add missing include for hub6_match_port()")
> Fixes: 3d406299d882 ("serial: 8250_hub6: add hub6_match_port()")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> drivers/tty/serial/8250/8250.h | 15 -------
> drivers/tty/serial/8250/8250_core.c | 2 -
> drivers/tty/serial/8250/8250_hub6.c | 60 -------------------------
> drivers/tty/serial/8250/8250_platform.c | 11 +----
> drivers/tty/serial/8250/8250_port.c | 23 ----------
> drivers/tty/serial/8250/Kconfig | 15 ++-----
> drivers/tty/serial/8250/Makefile | 1 -
> drivers/tty/serial/atmel_serial.c | 2 -
> drivers/tty/serial/fsl_lpuart.c | 2 -
> drivers/tty/serial/imx.c | 2 -
For freescale part.
Acked-by: Frank Li <Frank.Li@xxxxxxx>
> drivers/tty/serial/mpc52xx_uart.c | 3 +-
> drivers/tty/serial/sa1100.c | 2 -
> drivers/tty/serial/serial_core.c | 18 +++-----
> drivers/tty/serial/sunsu.c | 9 ----
> drivers/tty/serial/xilinx_uartps.c | 2 -
> include/linux/serial_8250.h | 2 -
> include/linux/serial_core.h | 2 -
> 17 files changed, 12 insertions(+), 159 deletions(-)
> delete mode 100644 drivers/tty/serial/8250/8250_hub6.c
>
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index 21ed9c41b751..75afeb8c0cef 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -323,14 +323,6 @@ static inline int serial8250_pnp_init(void) { return 0; }
> static inline void serial8250_pnp_exit(void) { }
> #endif
>
> -#ifdef CONFIG_SERIAL_8250_HUB6
> -int serial8250_hub6_init(void);
> -void serial8250_hub6_exit(void);
> -#else
> -static inline int serial8250_hub6_init(void) { return 0; }
> -static inline void serial8250_hub6_exit(void) { }
> -#endif
> -
> #ifdef CONFIG_SERIAL_8250_RSA
> void univ8250_rsa_support(struct uart_ops *ops, const struct uart_ops *core_ops);
> void rsa_enable(struct uart_8250_port *up);
> @@ -351,13 +343,6 @@ int fintek_8250_probe(struct uart_8250_port *uart);
> static inline int fintek_8250_probe(struct uart_8250_port *uart) { return 0; }
> #endif
>
> -#if IS_ENABLED(CONFIG_SERIAL_8250_HUB6)
> -bool hub6_match_port(const struct uart_port *port1, const struct uart_port *port2);
> -#else
> -static inline bool hub6_match_port(const struct uart_port *port1, const struct uart_port *port2)
> -{ return false; }
> -#endif
> -
> #ifdef CONFIG_ARCH_OMAP1
> #include <linux/soc/ti/omap1-soc.h>
> static inline int is_omap1_8250(struct uart_8250_port *pt)
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 42319843cb5b..96c99f0ae683 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -686,8 +686,6 @@ static bool serial8250_match_port(const struct uart_port *port1,
> return false;
> else if (port1->iotype == UPIO_PORT)
> return port1->iobase == port2->iobase;
> - else if (port1->iotype == UPIO_HUB6)
> - return hub6_match_port(port1, port2);
> else if (uart_iotype_mmio(port1->iotype))
> return port1->mapbase == port2->mapbase;
> else
> diff --git a/drivers/tty/serial/8250/8250_hub6.c b/drivers/tty/serial/8250/8250_hub6.c
> deleted file mode 100644
> index 848d9723ac56..000000000000
> --- a/drivers/tty/serial/8250/8250_hub6.c
> +++ /dev/null
> @@ -1,60 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0
> -/*
> - * Copyright (C) 2005 Russell King.
> - * Data taken from include/asm-i386/serial.h
> - */
> -#include <linux/module.h>
> -#include <linux/init.h>
> -#include <linux/serial_8250.h>
> -
> -#include "8250.h"
> -
> -#define HUB6(card, port) \
> - { \
> - .iobase = 0x302, \
> - .irq = 3, \
> - .uartclk = 1843200, \
> - .iotype = UPIO_HUB6, \
> - .flags = UPF_BOOT_AUTOCONF, \
> - .hub6 = (card) << 6 | (port) << 3 | 1, \
> - }
> -
> -static struct plat_serial8250_port hub6_data[] = {
> - HUB6(0, 0),
> - HUB6(0, 1),
> - HUB6(0, 2),
> - HUB6(0, 3),
> - HUB6(0, 4),
> - HUB6(0, 5),
> - HUB6(1, 0),
> - HUB6(1, 1),
> - HUB6(1, 2),
> - HUB6(1, 3),
> - HUB6(1, 4),
> - HUB6(1, 5),
> - { },
> -};
> -
> -static struct platform_device hub6_device = {
> - .name = "serial8250",
> - .id = PLAT8250_DEV_HUB6,
> - .dev = {
> - .platform_data = hub6_data,
> - },
> -};
> -
> -bool hub6_match_port(const struct uart_port *port1, const struct uart_port *port2)
> -{
> - return port1->iobase == port2->iobase && port1->hub6 == port2->hub6;
> -}
> -EXPORT_SYMBOL_GPL(hub6_match_port);
> -
> -int __init serial8250_hub6_init(void)
> -{
> - return platform_device_register(&hub6_device);
> -}
> -
> -void serial8250_hub6_exit(void)
> -{
> - platform_device_unregister(&hub6_device);
> -}
> diff --git a/drivers/tty/serial/8250/8250_platform.c b/drivers/tty/serial/8250/8250_platform.c
> index 7ce7ad295fae..8aa769085bfa 100644
> --- a/drivers/tty/serial/8250/8250_platform.c
> +++ b/drivers/tty/serial/8250/8250_platform.c
> @@ -86,7 +86,6 @@ static void __init __serial8250_isa_init_ports(void)
> port->irqflags = 0;
> port->uartclk = old_serial_port[i].baud_base * 16;
> port->flags = old_serial_port[i].flags;
> - port->hub6 = 0;
> port->membase = old_serial_port[i].iomem_base;
> port->iotype = old_serial_port[i].io_type;
> port->regshift = old_serial_port[i].iomem_reg_shift;
> @@ -169,7 +168,6 @@ static int serial8250_probe_platform(struct platform_device *dev, struct plat_se
> uart->port.flags = p->flags;
> uart->port.mapbase = p->mapbase;
> uart->port.mapsize = p->mapsize;
> - uart->port.hub6 = p->hub6;
> uart->port.has_sysrq = p->has_sysrq;
> uart->port.private_data = p->private_data;
> uart->port.type = p->type;
> @@ -317,14 +315,10 @@ static int __init serial8250_init(void)
> if (ret)
> goto unreg_uart_drv;
>
> - ret = serial8250_hub6_init();
> - if (ret)
> - goto unreg_pnp;
> -
> serial8250_isa_devs = platform_device_alloc("serial8250", PLAT8250_DEV_LEGACY);
> if (!serial8250_isa_devs) {
> ret = -ENOMEM;
> - goto unreg_hub6;
> + goto unreg_pnp;
> }
>
> ret = platform_device_add(serial8250_isa_devs);
> @@ -340,8 +334,6 @@ static int __init serial8250_init(void)
> platform_device_del(serial8250_isa_devs);
> put_dev:
> platform_device_put(serial8250_isa_devs);
> -unreg_hub6:
> - serial8250_hub6_exit();
> unreg_pnp:
> serial8250_pnp_exit();
> unreg_uart_drv:
> @@ -369,7 +361,6 @@ static void __exit serial8250_exit(void)
> platform_driver_unregister(&serial8250_isa_driver);
> platform_device_unregister(isa_dev);
>
> - serial8250_hub6_exit();
> serial8250_pnp_exit();
>
> #ifdef CONFIG_SPARC
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 36b2b0a2c05c..3593e7209879 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -354,22 +354,6 @@ static void default_serial_dl_write(struct uart_8250_port *up, u32 value)
> serial_out(up, UART_DLM, value >> 8 & 0xff);
> }
>
> -#ifdef CONFIG_HAS_IOPORT
> -static u32 hub6_serial_in(struct uart_port *p, unsigned int offset)
> -{
> - offset = offset << p->regshift;
> - outb(p->hub6 - 1 + offset, p->iobase);
> - return inb(p->iobase + 1);
> -}
> -
> -static void hub6_serial_out(struct uart_port *p, unsigned int offset, u32 value)
> -{
> - offset = offset << p->regshift;
> - outb(p->hub6 - 1 + offset, p->iobase);
> - outb(value, p->iobase + 1);
> -}
> -#endif /* CONFIG_HAS_IOPORT */
> -
> static u32 mem_serial_in(struct uart_port *p, unsigned int offset)
> {
> offset = offset << p->regshift;
> @@ -450,13 +434,6 @@ static void set_io_from_upio(struct uart_port *p)
> up->dl_write = default_serial_dl_write;
>
> switch (p->iotype) {
> -#ifdef CONFIG_HAS_IOPORT
> - case UPIO_HUB6:
> - p->serial_in = hub6_serial_in;
> - p->serial_out = hub6_serial_out;
> - break;
> -#endif
> -
> case UPIO_MEM:
> p->serial_in = mem_serial_in;
> p->serial_out = mem_serial_out;
> diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
> index 82e761b8298a..9917b7e1bb26 100644
> --- a/drivers/tty/serial/8250/Kconfig
> +++ b/drivers/tty/serial/8250/Kconfig
> @@ -208,9 +208,9 @@ config SERIAL_8250_EXTENDED
> depends on SERIAL_8250
> help
> If you wish to use any non-standard features of the standard "dumb"
> - driver, say Y here. This includes HUB6 support, shared serial
> - interrupts, special multiport support, support for more than the
> - four COM 1/2/3/4 boards, etc.
> + driver, say Y here. This includes shared serial interrupts, special
> + multiport support, support for more than the four COM 1/2/3/4 boards,
> + etc.
>
> Note that the answer to this question won't directly affect the
> kernel: saying N will just cause the configurator to skip all
> @@ -303,15 +303,6 @@ config SERIAL_8250_EXAR_ST16C554
> To compile this driver as a module, choose M here: the module
> will be called 8250_exar_st16c554.
>
> -config SERIAL_8250_HUB6
> - bool "Support Hub6 cards"
> - depends on SERIAL_8250_MANY_PORTS && ISA
> - help
> - Say Y here if you have a HUB6 serial board.
> -
> - To compile this driver as a module, choose M here: the module
> - will be called 8250_hub6.
> -
> config SERIAL_8250_PCI1XXXX
> tristate "Microchip 8250 based serial port"
> depends on SERIAL_8250 && PCI
> diff --git a/drivers/tty/serial/8250/Makefile b/drivers/tty/serial/8250/Makefile
> index 5ff2ba414e13..d241ce486953 100644
> --- a/drivers/tty/serial/8250/Makefile
> +++ b/drivers/tty/serial/8250/Makefile
> @@ -7,7 +7,6 @@ obj-$(CONFIG_SERIAL_8250) += 8250.o
> 8250-y := 8250_core.o
> 8250-y += 8250_platform.o
> 8250-$(CONFIG_SERIAL_8250_PNP) += 8250_pnp.o
> -8250-$(CONFIG_SERIAL_8250_HUB6) += 8250_hub6.o
>
> obj-$(CONFIG_SERIAL_8250) += 8250_base.o
> 8250_base-y := 8250_port.o
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index c3880259e3bc..9c40ccee0c82 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -2448,8 +2448,6 @@ static int atmel_verify_port(struct uart_port *port, struct serial_struct *ser)
> ret = -EINVAL;
> if (port->iobase != ser->port)
> ret = -EINVAL;
> - if (ser->hub6 != 0)
> - ret = -EINVAL;
> return ret;
> }
>
> diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
> index c8575c965203..6e1248840022 100644
> --- a/drivers/tty/serial/fsl_lpuart.c
> +++ b/drivers/tty/serial/fsl_lpuart.c
> @@ -2432,8 +2432,6 @@ static int lpuart_verify_port(struct uart_port *port, struct serial_struct *ser)
> ret = -EINVAL;
> if (port->iobase != ser->port)
> ret = -EINVAL;
> - if (ser->hub6 != 0)
> - ret = -EINVAL;
> return ret;
> }
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 986fefb45c63..d89be62e3852 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -1936,8 +1936,6 @@ imx_uart_verify_port(struct uart_port *port, struct serial_struct *ser)
> ret = -EINVAL;
> if (port->iobase != ser->port)
> ret = -EINVAL;
> - if (ser->hub6 != 0)
> - ret = -EINVAL;
> return ret;
> }
>
> diff --git a/drivers/tty/serial/mpc52xx_uart.c b/drivers/tty/serial/mpc52xx_uart.c
> index 472ec39caf27..240009333fb5 100644
> --- a/drivers/tty/serial/mpc52xx_uart.c
> +++ b/drivers/tty/serial/mpc52xx_uart.c
> @@ -1339,8 +1339,7 @@ mpc52xx_uart_verify_port(struct uart_port *port, struct serial_struct *ser)
> if ((ser->irq != port->irq) ||
> (ser->io_type != UPIO_MEM) ||
> (ser->baud_base != port->uartclk) ||
> - (ser->iomem_base != (void *)port->mapbase) ||
> - (ser->hub6 != 0))
> + (ser->iomem_base != (void *)port->mapbase))
> return -EINVAL;
>
> return 0;
> diff --git a/drivers/tty/serial/sa1100.c b/drivers/tty/serial/sa1100.c
> index 72b1bb76415c..ee5f3960d1e4 100644
> --- a/drivers/tty/serial/sa1100.c
> +++ b/drivers/tty/serial/sa1100.c
> @@ -556,8 +556,6 @@ sa1100_verify_port(struct uart_port *port, struct serial_struct *ser)
> ret = -EINVAL;
> if (sport->port.iobase != ser->port)
> ret = -EINVAL;
> - if (ser->hub6 != 0)
> - ret = -EINVAL;
> return ret;
> }
>
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 9eea8d1a0e8a..15d8c3ed6edc 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -812,7 +812,7 @@ static int uart_get_info(struct tty_port *port, struct serial_struct *retinfo)
> ASYNC_CLOSING_WAIT_NONE :
> jiffies_to_msecs(port->closing_wait) / 10;
> retinfo->custom_divisor = uport->custom_divisor;
> - retinfo->hub6 = uport->hub6;
> + retinfo->hub6 = 0;
> retinfo->io_type = uport->iotype;
> retinfo->iomem_reg_shift = uport->regshift;
> retinfo->iomem_base = (void *)(unsigned long)uport->mapbase;
> @@ -834,13 +834,12 @@ static int uart_change_port(struct uart_port *uport,
> unsigned long new_port)
> {
> unsigned long old_iobase, old_mapbase;
> - unsigned int old_type, old_iotype, old_hub6, old_shift;
> + unsigned int old_type, old_iotype, old_shift;
> int retval;
>
> old_iobase = uport->iobase;
> old_mapbase = uport->mapbase;
> old_type = uport->type;
> - old_hub6 = uport->hub6;
> old_iotype = uport->iotype;
> old_shift = uport->regshift;
>
> @@ -849,7 +848,6 @@ static int uart_change_port(struct uart_port *uport,
>
> uport->iobase = new_port;
> uport->type = new_info->type;
> - uport->hub6 = new_info->hub6;
> uport->iotype = new_info->io_type;
> uport->regshift = new_info->iomem_reg_shift;
> uport->mapbase = (unsigned long)new_info->iomem_base;
> @@ -867,7 +865,6 @@ static int uart_change_port(struct uart_port *uport,
> */
> uport->iobase = old_iobase;
> uport->type = old_type;
> - uport->hub6 = old_hub6;
> uport->iotype = old_iotype;
> uport->regshift = old_shift;
> uport->mapbase = old_mapbase;
> @@ -924,7 +921,6 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
> change_port = !(uport->flags & UPF_FIXED_PORT)
> && (new_port != uport->iobase ||
> (unsigned long)new_info->iomem_base != uport->mapbase ||
> - new_info->hub6 != uport->hub6 ||
> new_info->io_type != uport->iotype ||
> new_info->iomem_reg_shift != uport->regshift ||
> new_info->type != uport->type);
> @@ -954,6 +950,10 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
> goto check_and_exit;
> }
>
> + /* hub6 is no longer support */
> + if (new_info->hub6 != 0)
> + return -EINVAL;
> +
> if (change_irq || change_port) {
> retval = security_locked_down(LOCKDOWN_TIOCSSERIAL);
> if (retval)
> @@ -2010,7 +2010,6 @@ bool uart_iotype_io(enum uart_iotype iotype)
> {
> switch (iotype) {
> case UPIO_PORT:
> - case UPIO_HUB6:
> return true;
> default:
> return false;
> @@ -2538,10 +2537,7 @@ void uart_get_ioinfos(struct uart_port *port, char *buf, size_t size)
> if (uart_iotype_mmio(port->iotype)) {
> scnprintf(buf, size, " MMIO%s:%pa", uart_get_mmio_width(port), &port->mapbase);
> } else if (uart_iotype_io(port->iotype)) {
> - if (port->iotype == UPIO_PORT)
> - scnprintf(buf, size, " I/O:0x%lx", port->iobase);
> - else if (port->iotype == UPIO_HUB6)
> - scnprintf(buf, size, " I/O:0x%lx, offset 0x%x", port->iobase, port->hub6);
> + scnprintf(buf, size, " I/O:0x%lx", port->iobase);
> }
> }
> EXPORT_SYMBOL(uart_get_ioinfos);
> diff --git a/drivers/tty/serial/sunsu.c b/drivers/tty/serial/sunsu.c
> index 4ff3e5c41dab..f43b802add12 100644
> --- a/drivers/tty/serial/sunsu.c
> +++ b/drivers/tty/serial/sunsu.c
> @@ -106,10 +106,6 @@ static unsigned int serial_in(struct uart_sunsu_port *up, int offset)
> offset <<= up->port.regshift;
>
> switch (up->port.iotype) {
> - case UPIO_HUB6:
> - outb(up->port.hub6 - 1 + offset, up->port.iobase);
> - return inb(up->port.iobase + 1);
> -
> case UPIO_MEM:
> return readb(up->port.membase + offset);
>
> @@ -136,11 +132,6 @@ static void serial_out(struct uart_sunsu_port *up, int offset, int value)
> offset <<= up->port.regshift;
>
> switch (up->port.iotype) {
> - case UPIO_HUB6:
> - outb(up->port.hub6 - 1 + offset, up->port.iobase);
> - outb(value, up->port.iobase + 1);
> - break;
> -
> case UPIO_MEM:
> writeb(value, up->port.membase + offset);
> break;
> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> index a072b75dbaf2..4066cc99fe1a 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -1079,8 +1079,6 @@ static int cdns_uart_verify_port(struct uart_port *port,
> return -EINVAL;
> if (port->iobase != ser->port)
> return -EINVAL;
> - if (ser->hub6 != 0)
> - return -EINVAL;
> return 0;
> }
>
> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
> index d91c0477be9d..d55bce4d4709 100644
> --- a/include/linux/serial_8250.h
> +++ b/include/linux/serial_8250.h
> @@ -41,7 +41,6 @@ struct plat_serial8250_port {
> void *private_data;
> unsigned char regshift; /* register shift */
> unsigned char iotype; /* UPIO_* */
> - unsigned char hub6;
> unsigned char has_sysrq; /* supports magic SysRq */
> unsigned int type; /* If UPF_FIXED_TYPE */
> upf_t flags; /* UPF_* flags */
> @@ -75,7 +74,6 @@ enum {
> PLAT8250_DEV_ACCENT,
> PLAT8250_DEV_BOCA,
> PLAT8250_DEV_EXAR_ST16C554,
> - PLAT8250_DEV_HUB6,
> PLAT8250_DEV_AU1X00,
> PLAT8250_DEV_SM501,
> };
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 4eeb8253752a..ca8d009e5c36 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -430,7 +430,6 @@ typedef unsigned int __bitwise upstat_t;
> enum uart_iotype {
> UPIO_UNKNOWN = -1,
> UPIO_PORT = SERIAL_IO_PORT, /* 8b I/O port access */
> - UPIO_HUB6 = SERIAL_IO_HUB6, /* Hub6 ISA card */
> UPIO_MEM = SERIAL_IO_MEM, /* driver-specific */
> UPIO_MEM32 = SERIAL_IO_MEM32, /* 32b little endian */
> UPIO_AU = SERIAL_IO_AU, /* Au1x00 and RT288x type IO */
> @@ -590,7 +589,6 @@ struct uart_port {
> unsigned char has_sysrq;
> unsigned char sysrq_seq; /* index in sysrq_toggle_seq */
>
> - unsigned char hub6; /* this should be in the 8250 driver */
> unsigned char suspended;
> unsigned char console_reinit;
> const char *name; /* port name */
> --
> 2.53.0
>