// SPDX-License-Identifier: GPL-2.0+
/*
 *  Universal/legacy driver for 8250/16550-type serial ports
 *
 *  Based on drivers/char/serial.c, by Linus Torvalds, Theodore Ts'o.
 *
 *  Copyright (C) 2001 Russell King.
 *
 *  Supports:
 *            early_serial_setup() ports
 *            userspace-configurable "phantom" ports
 *            serial8250_register_8250_port() ports
 */

#include <linux/acpi.h>
#include <linux/hashtable.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/ioport.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/sysrq.h>
#include <linux/delay.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
#include <linux/tty.h>
#include <linux/ratelimit.h>
#include <linux/tty_flip.h>
#include <linux/serial.h>
#include <linux/serial_8250.h>
#include <linux/nmi.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/string_helpers.h>
#include <linux/uaccess.h>
#include <linux/io.h>

#include <asm/irq.h>

#include "8250.h"

#define PASS_LIMIT      512

struct irq_info {
        struct                  hlist_node node;
        int                     irq;
        spinlock_t              lock;   /* Protects list not the hash */
        struct list_head        *head;
};

#define IRQ_HASH_BITS           5       /* Can be adjusted later */
static DEFINE_HASHTABLE(irq_lists, IRQ_HASH_BITS);
static DEFINE_MUTEX(hash_mutex);        /* Used to walk the hash */

static bool skip_txen_test;
module_param(skip_txen_test, bool, 0644);
MODULE_PARM_DESC(skip_txen_test, "Skip checking for the TXEN bug at init time");

/*
 * This is the serial driver's interrupt routine.
 *
 * Arjan thinks the old way was overly complex, so it got simplified.
 * Alan disagrees, saying that need the complexity to handle the weird
 * nature of ISA shared interrupts.  (This is a special exception.)
 *
 * In order to handle ISA shared interrupts properly, we need to check
 * that all ports have been serviced, and therefore the ISA interrupt
 * line has been de-asserted.
 *
 * This means we need to loop through all ports. checking that they
 * don't have an interrupt pending.
 */
static irqreturn_t serial8250_interrupt(int irq, void *dev_id)
{
        struct irq_info *i = dev_id;
        struct list_head *l, *end = NULL;
        int pass_counter = 0, handled = 0;

        guard(spinlock)(&i->lock);

        l = i->head;
        do {
                struct uart_8250_port *up = list_entry(l, struct uart_8250_port, list);
                struct uart_port *port = &up->port;

                if (port->handle_irq(port)) {
                        handled = 1;
                        end = NULL;
                } else if (end == NULL)
                        end = l;

                l = l->next;

                if (l == i->head && pass_counter++ > PASS_LIMIT)
                        break;
        } while (l != end);

        return IRQ_RETVAL(handled);
}

/*
 * To support ISA shared interrupts, we need to have one interrupt
 * handler that ensures that the IRQ line has been deasserted
 * before returning.  Failing to do this will result in the IRQ
 * line being stuck active, and, since ISA irqs are edge triggered,
 * no more IRQs will be seen.
 */
static void serial_do_unlink(struct irq_info *i, struct uart_8250_port *up)
{
        spin_lock_irq(&i->lock);

        if (!list_empty(i->head)) {
                if (i->head == &up->list)
                        i->head = i->head->next;
                list_del(&up->list);
        } else {
                BUG_ON(i->head != &up->list);
                i->head = NULL;
        }
        spin_unlock_irq(&i->lock);
        /* List empty so throw away the hash node */
        if (i->head == NULL) {
                hlist_del(&i->node);
                kfree(i);
        }
}

/*
 * Either:
 * - find the corresponding info in the hashtable and return it, or
 * - allocate a new one, add it to the hashtable and return it.
 */
static struct irq_info *serial_get_or_create_irq_info(const struct uart_8250_port *up)
{
        struct irq_info *i;

        guard(mutex)(&hash_mutex);

        hash_for_each_possible(irq_lists, i, node, up->port.irq)
                if (i->irq == up->port.irq)
                        return i;

        i = kzalloc_obj(*i);
        if (i == NULL)
                return ERR_PTR(-ENOMEM);

        spin_lock_init(&i->lock);
        i->irq = up->port.irq;
        hash_add(irq_lists, &i->node, i->irq);

        return i;
}

static int serial_link_irq_chain(struct uart_8250_port *up)
{
        struct irq_info *i;
        int ret;

        i = serial_get_or_create_irq_info(up);
        if (IS_ERR(i))
                return PTR_ERR(i);

        scoped_guard(spinlock_irq, &i->lock) {
                if (i->head) {
                        list_add(&up->list, i->head);

                        return 0;
                }

                INIT_LIST_HEAD(&up->list);
                i->head = &up->list;
        }

        ret = request_irq(up->port.irq, serial8250_interrupt, up->port.irqflags, up->port.name, i);
        if (ret < 0)
                serial_do_unlink(i, up);

        return ret;
}

static void serial_unlink_irq_chain(struct uart_8250_port *up)
{
        struct irq_info *i;

        guard(mutex)(&hash_mutex);

        hash_for_each_possible(irq_lists, i, node, up->port.irq)
                if (i->irq == up->port.irq) {
                        if (WARN_ON(i->head == NULL))
                                return;

                        if (list_empty(i->head))
                                free_irq(up->port.irq, i);

                        serial_do_unlink(i, up);

                        return;
                }

        WARN_ON(1);
}

/*
 * This function is used to handle ports that do not have an
 * interrupt.  This doesn't work very well for 16450's, but gives
 * barely passable results for a 16550A.  (Although at the expense
 * of much CPU overhead).
 */
static void serial8250_timeout(struct timer_list *t)
{
        struct uart_8250_port *up = timer_container_of(up, t, timer);

        up->port.handle_irq(&up->port);
        mod_timer(&up->timer, jiffies + uart_poll_timeout(&up->port));
}

static void serial8250_backup_timeout(struct timer_list *t)
{
        struct uart_8250_port *up = timer_container_of(up, t, timer);
        unsigned int iir, ier = 0, lsr;
        unsigned long flags;

        uart_port_lock_irqsave(&up->port, &flags);

        /*
         * Must disable interrupts or else we risk racing with the interrupt
         * based handler.
         */
        if (up->port.irq) {
                ier = serial_in(up, UART_IER);
                serial_out(up, UART_IER, 0);
        }

        iir = serial_in(up, UART_IIR);

        /*
         * This should be a safe test for anyone who doesn't trust the
         * IIR bits on their UART, but it's specifically designed for
         * the "Diva" UART used on the management processor on many HP
         * ia64 and parisc boxes.
         */
        lsr = serial_lsr_in(up);
        if ((iir & UART_IIR_NO_INT) && (up->ier & UART_IER_THRI) &&
            (!kfifo_is_empty(&up->port.state->port.xmit_fifo) ||
             up->port.x_char) &&
            (lsr & UART_LSR_THRE)) {
                iir &= ~(UART_IIR_ID | UART_IIR_NO_INT);
                iir |= UART_IIR_THRI;
        }

        if (!(iir & UART_IIR_NO_INT))
                serial8250_tx_chars(up);

        if (up->port.irq)
                serial_out(up, UART_IER, ier);

        uart_port_unlock_irqrestore(&up->port, flags);

        /* Standard timer interval plus 0.2s to keep the port running */
        mod_timer(&up->timer,
                jiffies + uart_poll_timeout(&up->port) + HZ / 5);
}

static void univ8250_setup_timer(struct uart_8250_port *up)
{
        struct uart_port *port = &up->port;

        /*
         * The above check will only give an accurate result the first time
         * the port is opened so this value needs to be preserved.
         */
        if (up->bugs & UART_BUG_THRE) {
                pr_debug("%s - using backup timer\n", port->name);

                up->timer.function = serial8250_backup_timeout;
                mod_timer(&up->timer, jiffies +
                          uart_poll_timeout(port) + HZ / 5);
        }

        /*
         * If the "interrupt" for this port doesn't correspond with any
         * hardware interrupt, we use a timer-based system.  The original
         * driver used to do this with IRQ0.
         */
        if (!port->irq)
                mod_timer(&up->timer, jiffies + uart_poll_timeout(port));
}

static int univ8250_setup_irq(struct uart_8250_port *up)
{
        struct uart_port *port = &up->port;

        if (port->irq)
                return serial_link_irq_chain(up);

        return 0;
}

static void univ8250_release_irq(struct uart_8250_port *up)
{
        struct uart_port *port = &up->port;

        timer_delete_sync(&up->timer);
        up->timer.function = serial8250_timeout;
        if (port->irq)
                serial_unlink_irq_chain(up);
}

const struct uart_ops *univ8250_port_base_ops;
struct uart_ops univ8250_port_ops;

static const struct uart_8250_ops univ8250_driver_ops = {
        .setup_irq      = univ8250_setup_irq,
        .release_irq    = univ8250_release_irq,
        .setup_timer    = univ8250_setup_timer,
};

static struct uart_8250_port serial8250_ports[UART_NR];

/**
 * serial8250_get_port - retrieve struct uart_8250_port
 * @line: serial line number
 *
 * This function retrieves struct uart_8250_port for the specific line.
 * This struct *must* *not* be used to perform a 8250 or serial core operation
 * which is not accessible otherwise. Its only purpose is to make the struct
 * accessible to the runtime-pm callbacks for context suspend/restore.
 * The lock assumption made here is none because runtime-pm suspend/resume
 * callbacks should not be invoked if there is any operation performed on the
 * port.
 */
struct uart_8250_port *serial8250_get_port(int line)
{
        return &serial8250_ports[line];
}
EXPORT_SYMBOL_GPL(serial8250_get_port);

static inline void serial8250_apply_quirks(struct uart_8250_port *up)
{
        up->port.quirks |= skip_txen_test ? UPQ_NO_TXEN_TEST : 0;
}

struct uart_8250_port *serial8250_setup_port(int index)
{
        struct uart_8250_port *up;

        if (index >= UART_NR)
                return NULL;

        up = &serial8250_ports[index];
        up->port.line = index;
        up->port.port_id = index;

        serial8250_init_port(up);
        if (!univ8250_port_base_ops)
                univ8250_port_base_ops = up->port.ops;
        up->port.ops = &univ8250_port_ops;

        timer_setup(&up->timer, serial8250_timeout, 0);

        up->ops = &univ8250_driver_ops;

        serial8250_set_defaults(up);

        return up;
}

void __init serial8250_register_ports(struct uart_driver *drv, struct device *dev)
{
        int i;

        for (i = 0; i < nr_uarts; i++) {
                struct uart_8250_port *up = &serial8250_ports[i];

                if (up->port.type == PORT_8250_CIR)
                        continue;

                if (up->port.dev)
                        continue;

                up->port.dev = dev;

                if (uart_console_registered(&up->port))
                        pm_runtime_get_sync(up->port.dev);

                serial8250_apply_quirks(up);
                uart_add_one_port(drv, &up->port);
        }
}

#ifdef CONFIG_SERIAL_8250_CONSOLE

static void univ8250_console_write(struct console *co, const char *s,
                                   unsigned int count)
{
        struct uart_8250_port *up = &serial8250_ports[co->index];

        serial8250_console_write(up, s, count);
}

static int univ8250_console_setup(struct console *co, char *options)
{
        struct uart_8250_port *up;
        struct uart_port *port;
        int retval, i;

        /*
         * Check whether an invalid uart number has been specified, and
         * if so, search for the first available port that does have
         * console support.
         */
        if (co->index < 0 || co->index >= UART_NR)
                co->index = 0;

        /*
         * If the console is past the initial isa ports, init more ports up to
         * co->index as needed and increment nr_uarts accordingly.
         */
        for (i = nr_uarts; i <= co->index; i++) {
                up = serial8250_setup_port(i);
                if (!up)
                        return -ENODEV;
                nr_uarts++;
        }

        port = &serial8250_ports[co->index].port;
        /* link port to console */
        uart_port_set_cons(port, co);

        retval = serial8250_console_setup(port, options, false);
        if (retval != 0)
                uart_port_set_cons(port, NULL);
        return retval;
}

static int univ8250_console_exit(struct console *co)
{
        struct uart_port *port;

        port = &serial8250_ports[co->index].port;
        return serial8250_console_exit(port);
}

/**
 *      univ8250_console_match - non-standard console matching
 *      @co:      registering console
 *      @name:    name from console command line
 *      @idx:     index from console command line
 *      @options: ptr to option string from console command line
 *
 *      Only attempts to match console command lines of the form:
 *          console=uart[8250],io|mmio|mmio16|mmio32,<addr>[,<options>]
 *          console=uart[8250],0x<addr>[,<options>]
 *      This form is used to register an initial earlycon boot console and
 *      replace it with the serial8250_console at 8250 driver init.
 *
 *      Performs console setup for a match (as required by interface)
 *      If no <options> are specified, then assume the h/w is already setup.
 *
 *      Returns 0 if console matches; otherwise non-zero to use default matching
 */
static int univ8250_console_match(struct console *co, char *name, int idx,
                                  char *options)
{
        char match[] = "uart";  /* 8250-specific earlycon name */
        enum uart_iotype iotype;
        resource_size_t addr;
        int i;

        if (strncmp(name, match, 4) != 0)
                return -ENODEV;

        if (uart_parse_earlycon(options, &iotype, &addr, &options))
                return -ENODEV;

        /* try to match the port specified on the command line */
        for (i = 0; i < nr_uarts; i++) {
                struct uart_port *port = &serial8250_ports[i].port;

                if (port->iotype != iotype)
                        continue;
                if ((iotype == UPIO_MEM || iotype == UPIO_MEM16 ||
                     iotype == UPIO_MEM32 || iotype == UPIO_MEM32BE)
                    && (port->mapbase != addr))
                        continue;
                if (iotype == UPIO_PORT && port->iobase != addr)
                        continue;

                co->index = i;
                uart_port_set_cons(port, co);
                return serial8250_console_setup(port, options, true);
        }

        return -ENODEV;
}

static struct console univ8250_console = {
        .name           = "ttyS",
        .write          = univ8250_console_write,
        .device         = uart_console_device,
        .setup          = univ8250_console_setup,
        .exit           = univ8250_console_exit,
        .match          = univ8250_console_match,
        .flags          = CON_PRINTBUFFER | CON_ANYTIME,
        .index          = -1,
        .data           = &serial8250_reg,
};

static int __init univ8250_console_init(void)
{
        if (nr_uarts == 0)
                return -ENODEV;

        serial8250_isa_init_ports();
        register_console(&univ8250_console);
        return 0;
}
console_initcall(univ8250_console_init);

#define SERIAL8250_CONSOLE      (&univ8250_console)
#else
#define SERIAL8250_CONSOLE      NULL
#endif

struct uart_driver serial8250_reg = {
        .owner                  = THIS_MODULE,
        .driver_name            = "serial",
        .dev_name               = "ttyS",
        .major                  = TTY_MAJOR,
        .minor                  = 64,
        .cons                   = SERIAL8250_CONSOLE,
};

/*
 * early_serial_setup - early registration for 8250 ports
 *
 * Setup an 8250 port structure prior to console initialisation.  Use
 * after console initialisation will cause undefined behaviour.
 */
int __init early_serial_setup(struct uart_port *port)
{
        struct uart_port *p;

        if (port->line >= ARRAY_SIZE(serial8250_ports) || nr_uarts == 0)
                return -ENODEV;

        serial8250_isa_init_ports();
        p = &serial8250_ports[port->line].port;
        p->iobase       = port->iobase;
        p->membase      = port->membase;
        p->irq          = port->irq;
        p->irqflags     = port->irqflags;
        p->uartclk      = port->uartclk;
        p->fifosize     = port->fifosize;
        p->regshift     = port->regshift;
        p->iotype       = port->iotype;
        p->flags        = port->flags;
        p->mapbase      = port->mapbase;
        p->mapsize      = port->mapsize;
        p->private_data = port->private_data;
        p->type         = port->type;
        p->line         = port->line;

        serial8250_set_defaults(up_to_u8250p(p));

        if (port->serial_in)
                p->serial_in = port->serial_in;
        if (port->serial_out)
                p->serial_out = port->serial_out;
        if (port->handle_irq)
                p->handle_irq = port->handle_irq;

        return 0;
}

/**
 *      serial8250_suspend_port - suspend one serial port
 *      @line:  serial line number
 *
 *      Suspend one serial port.
 */
void serial8250_suspend_port(int line)
{
        struct uart_8250_port *up = &serial8250_ports[line];
        struct uart_port *port = &up->port;

        if (!console_suspend_enabled && uart_console(port) &&
            port->type != PORT_8250) {
                unsigned char canary = 0xa5;

                serial_out(up, UART_SCR, canary);
                if (serial_in(up, UART_SCR) == canary)
                        up->canary = canary;
        }

        uart_suspend_port(&serial8250_reg, port);
}
EXPORT_SYMBOL(serial8250_suspend_port);

/**
 *      serial8250_resume_port - resume one serial port
 *      @line:  serial line number
 *
 *      Resume one serial port.
 */
void serial8250_resume_port(int line)
{
        struct uart_8250_port *up = &serial8250_ports[line];
        struct uart_port *port = &up->port;

        up->canary = 0;

        if (up->capabilities & UART_NATSEMI) {
                /* Ensure it's still in high speed mode */
                serial_port_out(port, UART_LCR, 0xE0);

                ns16550a_goto_highspeed(up);

                serial_port_out(port, UART_LCR, 0);
                port->uartclk = 921600*16;
        }
        uart_resume_port(&serial8250_reg, port);
}
EXPORT_SYMBOL(serial8250_resume_port);

/*
 * serial8250_register_8250_port and serial8250_unregister_port allows for
 * 16x50 serial ports to be configured at run-time, to support PCMCIA
 * modems and PCI multiport cards.
 */
static DEFINE_MUTEX(serial_mutex);

static struct uart_8250_port *serial8250_find_match_or_unused(const struct uart_port *port)
{
        int i;

        /*
         * First, find a port entry which matches.
         */
        for (i = 0; i < nr_uarts; i++)
                if (uart_match_port(&serial8250_ports[i].port, port))
                        return &serial8250_ports[i];

        /* try line number first if still available */
        i = port->line;
        if (i < nr_uarts && serial8250_ports[i].port.type == PORT_UNKNOWN &&
                        serial8250_ports[i].port.iobase == 0)
                return &serial8250_ports[i];
        /*
         * We didn't find a matching entry, so look for the first
         * free entry.  We look for one which hasn't been previously
         * used (indicated by zero iobase).
         */
        for (i = 0; i < nr_uarts; i++)
                if (serial8250_ports[i].port.type == PORT_UNKNOWN &&
                    serial8250_ports[i].port.iobase == 0)
                        return &serial8250_ports[i];

        /*
         * That also failed.  Last resort is to find any entry which
         * doesn't have a real port associated with it.
         */
        for (i = 0; i < nr_uarts; i++)
                if (serial8250_ports[i].port.type == PORT_UNKNOWN)
                        return &serial8250_ports[i];

        return NULL;
}

static void serial_8250_overrun_backoff_work(struct work_struct *work)
{
        struct uart_8250_port *up = container_of(to_delayed_work(work), struct uart_8250_port,
                                                 overrun_backoff);

        guard(uart_port_lock_irqsave)(&up->port);
        up->ier |= UART_IER_RLSI | UART_IER_RDI;
        serial_out(up, UART_IER, up->ier);
}

/**
 *      serial8250_register_8250_port - register a serial port
 *      @up: serial port template
 *
 *      Configure the serial port specified by the request. If the
 *      port exists and is in use, it is hung up and unregistered
 *      first.
 *
 *      The port is then probed and if necessary the IRQ is autodetected
 *      If this fails an error is returned.
 *
 *      On success the port is ready to use and the line number is returned.
 */
int serial8250_register_8250_port(const struct uart_8250_port *up)
{
        struct uart_8250_port *uart;
        int ret;

        if (up->port.uartclk == 0)
                return -EINVAL;

        guard(mutex)(&serial_mutex);

        uart = serial8250_find_match_or_unused(&up->port);
        if (!uart) {
                /*
                 * If the port is past the initial isa ports, initialize a new
                 * port and increment nr_uarts accordingly.
                 */
                uart = serial8250_setup_port(nr_uarts);
                if (!uart)
                        return -ENOSPC;
                nr_uarts++;
        }

        /* Check if it is CIR already. We check this below again, see there why. */
        if (uart->port.type == PORT_8250_CIR)
                return -ENODEV;

        if (uart->port.dev)
                uart_remove_one_port(&serial8250_reg, &uart->port);

        uart->port.ctrl_id      = up->port.ctrl_id;
        uart->port.port_id      = up->port.port_id;
        uart->port.iobase       = up->port.iobase;
        uart->port.membase      = up->port.membase;
        uart->port.irq          = up->port.irq;
        uart->port.irqflags     = up->port.irqflags;
        uart->port.uartclk      = up->port.uartclk;
        uart->port.fifosize     = up->port.fifosize;
        uart->port.regshift     = up->port.regshift;
        uart->port.iotype       = up->port.iotype;
        uart->port.flags        = up->port.flags | UPF_BOOT_AUTOCONF;
        uart->bugs              = up->bugs;
        uart->port.mapbase      = up->port.mapbase;
        uart->port.mapsize      = up->port.mapsize;
        uart->port.private_data = up->port.private_data;
        uart->tx_loadsz         = up->tx_loadsz;
        uart->capabilities      = up->capabilities;
        uart->port.throttle     = up->port.throttle;
        uart->port.unthrottle   = up->port.unthrottle;
        uart->port.rs485_config = up->port.rs485_config;
        uart->port.rs485_supported = up->port.rs485_supported;
        uart->port.rs485        = up->port.rs485;
        uart->rs485_start_tx    = up->rs485_start_tx;
        uart->rs485_stop_tx     = up->rs485_stop_tx;
        uart->lsr_save_mask     = up->lsr_save_mask;
        uart->dma               = up->dma;

        /* Take tx_loadsz from fifosize if it wasn't set separately */
        if (uart->port.fifosize && !uart->tx_loadsz)
                uart->tx_loadsz = uart->port.fifosize;

        if (up->port.dev) {
                uart->port.dev = up->port.dev;
                ret = uart_get_rs485_mode(&uart->port);
                if (ret)
                        goto err;
        }

        if (up->port.flags & UPF_FIXED_TYPE)
                uart->port.type = up->port.type;

        /*
         * Only call mctrl_gpio_init(), if the device has no ACPI
         * companion device
         */
        if (!has_acpi_companion(uart->port.dev)) {
                struct mctrl_gpios *gpios = mctrl_gpio_init(&uart->port, 0);
                if (IS_ERR(gpios)) {
                        ret = PTR_ERR(gpios);
                        goto err;
                } else {
                        uart->gpios = gpios;
                }
        }

        serial8250_set_defaults(uart);

        /* Possibly override default I/O functions.  */
        if (up->port.serial_in)
                uart->port.serial_in = up->port.serial_in;
        if (up->port.serial_out)
                uart->port.serial_out = up->port.serial_out;
        if (up->port.handle_irq)
                uart->port.handle_irq = up->port.handle_irq;
        /*  Possibly override set_termios call */
        if (up->port.set_termios)
                uart->port.set_termios = up->port.set_termios;
        if (up->port.set_ldisc)
                uart->port.set_ldisc = up->port.set_ldisc;
        if (up->port.get_mctrl)
                uart->port.get_mctrl = up->port.get_mctrl;
        if (up->port.set_mctrl)
                uart->port.set_mctrl = up->port.set_mctrl;
        if (up->port.get_divisor)
                uart->port.get_divisor = up->port.get_divisor;
        if (up->port.set_divisor)
                uart->port.set_divisor = up->port.set_divisor;
        if (up->port.startup)
                uart->port.startup = up->port.startup;
        if (up->port.shutdown)
                uart->port.shutdown = up->port.shutdown;
        if (up->port.pm)
                uart->port.pm = up->port.pm;
        if (up->port.handle_break)
                uart->port.handle_break = up->port.handle_break;
        if (up->dl_read)
                uart->dl_read = up->dl_read;
        if (up->dl_write)
                uart->dl_write = up->dl_write;

        /* Check the type (again)! It might have changed by the port.type assignment above. */
        if (uart->port.type != PORT_8250_CIR) {
                if (uart_console_registered(&uart->port))
                        pm_runtime_get_sync(uart->port.dev);

                if (serial8250_isa_config != NULL)
                        serial8250_isa_config(0, &uart->port,
                                        &uart->capabilities);

                serial8250_apply_quirks(uart);
                ret = uart_add_one_port(&serial8250_reg,
                                        &uart->port);
                if (ret)
                        goto err;

                ret = uart->port.line;
        } else {
                dev_info(uart->port.dev,
                        "skipping CIR port at 0x%lx / 0x%llx, IRQ %d\n",
                        uart->port.iobase,
                        (unsigned long long)uart->port.mapbase,
                        uart->port.irq);

                ret = 0;
        }

        if (!uart->lsr_save_mask)
                uart->lsr_save_mask = LSR_SAVE_FLAGS;   /* Use default LSR mask */

        /* Initialise interrupt backoff work if required */
        if (up->overrun_backoff_time_ms > 0) {
                uart->overrun_backoff_time_ms =
                        up->overrun_backoff_time_ms;
                INIT_DELAYED_WORK(&uart->overrun_backoff,
                                serial_8250_overrun_backoff_work);
        } else {
                uart->overrun_backoff_time_ms = 0;
        }

        return ret;

err:
        uart->port.dev = NULL;
        return ret;
}
EXPORT_SYMBOL(serial8250_register_8250_port);

/**
 *      serial8250_unregister_port - remove a 16x50 serial port at runtime
 *      @line: serial line number
 *
 *      Remove one serial port.  This may not be called from interrupt
 *      context.  We hand the port back to the our control.
 */
void serial8250_unregister_port(int line)
{
        struct uart_8250_port *uart = &serial8250_ports[line];

        guard(mutex)(&serial_mutex);

        if (uart->em485) {
                guard(uart_port_lock_irqsave)(&uart->port);
                serial8250_em485_destroy(uart);
        }

        uart_remove_one_port(&serial8250_reg, &uart->port);
        if (serial8250_isa_devs) {
                uart->port.flags &= ~UPF_BOOT_AUTOCONF;
                uart->port.type = PORT_UNKNOWN;
                uart->port.dev = &serial8250_isa_devs->dev;
                uart->port.port_id = line;
                uart->capabilities = 0;
                serial8250_init_port(uart);
                serial8250_apply_quirks(uart);
                uart_add_one_port(&serial8250_reg, &uart->port);
        } else {
                uart->port.dev = NULL;
        }
}
EXPORT_SYMBOL(serial8250_unregister_port);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Generic 8250/16x50 serial driver");