// SPDX-License-Identifier: GPL-2.0
/*
 *      linux/arch/alpha/kernel/srmcons.c
 *
 * Callback based driver for SRM Console console device.
 * (TTY driver and console driver)
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/delay.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/timer.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>

#include <asm/console.h>
#include <linux/uaccess.h>

#include "proto.h"


static DEFINE_SPINLOCK(srmcons_callback_lock);
static int srm_is_registered_console = 0;

/* 
 * The TTY driver
 */
#define MAX_SRM_CONSOLE_DEVICES 1       /* only support 1 console device */

struct srmcons_private {
        struct tty_port port;
        struct timer_list timer;
} srmcons_singleton;

typedef union _srmcons_result {
        struct {
                unsigned long c :61;
                unsigned long status :3;
        } bits;
        long as_long;
} srmcons_result;

/* called with callback_lock held */
static int
srmcons_do_receive_chars(struct tty_port *port)
{
        srmcons_result result;
        int count = 0, loops = 0;

        do {
                result.as_long = callback_getc(0);
                if (result.bits.status < 2) {
                        tty_insert_flip_char(port, (u8)result.bits.c, 0);
                        count++;
                }
        } while((result.bits.status & 1) && (++loops < 10));

        if (count)
                tty_flip_buffer_push(port);

        return count;
}

static void
srmcons_receive_chars(struct timer_list *t)
{
        struct srmcons_private *srmconsp = timer_container_of(srmconsp, t,
                                                              timer);
        struct tty_port *port = &srmconsp->port;
        unsigned long flags;
        int incr = 10;

        local_irq_save(flags);
        if (spin_trylock(&srmcons_callback_lock)) {
                if (!srmcons_do_receive_chars(port))
                        incr = 100;
                spin_unlock(&srmcons_callback_lock);
        } 

        spin_lock(&port->lock);
        if (port->tty)
                mod_timer(&srmconsp->timer, jiffies + incr);
        spin_unlock(&port->lock);

        local_irq_restore(flags);
}

/* called with callback_lock held */
static void
srmcons_do_write(struct tty_port *port, const u8 *buf, size_t count)
{
        size_t c;
        srmcons_result result;

        while (count > 0) {
                bool need_cr = false;
                /* 
                 * Break it up into reasonable size chunks to allow a chance
                 * for input to get in
                 */
                for (c = 0; c < min_t(size_t, 128U, count) && !need_cr; c++)
                        if (buf[c] == '\n')
                                need_cr = true;
                
                while (c > 0) {
                        result.as_long = callback_puts(0, buf, c);
                        c -= result.bits.c;
                        count -= result.bits.c;
                        buf += result.bits.c;

                        /*
                         * Check for pending input iff a tty port was provided
                         */
                        if (port)
                                srmcons_do_receive_chars(port);
                }

                while (need_cr) {
                        result.as_long = callback_puts(0, "\r", 1);
                        if (result.bits.c > 0)
                                need_cr = false;
                }
        }
}

static ssize_t
srmcons_write(struct tty_struct *tty, const u8 *buf, size_t count)
{
        unsigned long flags;

        spin_lock_irqsave(&srmcons_callback_lock, flags);
        srmcons_do_write(tty->port, buf, count);
        spin_unlock_irqrestore(&srmcons_callback_lock, flags);

        return count;
}

static unsigned int
srmcons_write_room(struct tty_struct *tty)
{
        return 512;
}

static int
srmcons_open(struct tty_struct *tty, struct file *filp)
{
        struct srmcons_private *srmconsp = &srmcons_singleton;
        struct tty_port *port = &srmconsp->port;
        unsigned long flags;

        spin_lock_irqsave(&port->lock, flags);

        if (!port->tty) {
                tty->driver_data = srmconsp;
                tty->port = port;
                port->tty = tty; /* XXX proper refcounting */
                mod_timer(&srmconsp->timer, jiffies + 10);
        }

        spin_unlock_irqrestore(&port->lock, flags);

        return 0;
}

static void
srmcons_close(struct tty_struct *tty, struct file *filp)
{
        struct srmcons_private *srmconsp = tty->driver_data;
        struct tty_port *port = &srmconsp->port;
        unsigned long flags;

        spin_lock_irqsave(&port->lock, flags);

        if (tty->count == 1) {
                port->tty = NULL;
                timer_delete(&srmconsp->timer);
        }

        spin_unlock_irqrestore(&port->lock, flags);
}


static struct tty_driver *srmcons_driver;

static const struct tty_operations srmcons_ops = {
        .open           = srmcons_open,
        .close          = srmcons_close,
        .write          = srmcons_write,
        .write_room     = srmcons_write_room,
};

static int __init
srmcons_init(void)
{
        struct tty_driver *driver;
        int err;

        timer_setup(&srmcons_singleton.timer, srmcons_receive_chars, 0);

        if (!srm_is_registered_console)
                return -ENODEV;

        driver = tty_alloc_driver(MAX_SRM_CONSOLE_DEVICES, 0);
        if (IS_ERR(driver))
                return PTR_ERR(driver);

        tty_port_init(&srmcons_singleton.port);

        driver->driver_name = "srm";
        driver->name = "srm";
        driver->major = 0;      /* dynamic */
        driver->minor_start = 0;
        driver->type = TTY_DRIVER_TYPE_SYSTEM;
        driver->subtype = SYSTEM_TYPE_SYSCONS;
        driver->init_termios = tty_std_termios;
        tty_set_operations(driver, &srmcons_ops);
        tty_port_link_device(&srmcons_singleton.port, driver, 0);
        err = tty_register_driver(driver);
        if (err)
                goto err_free_drv;

        srmcons_driver = driver;

        return 0;
err_free_drv:
        tty_driver_kref_put(driver);
        tty_port_destroy(&srmcons_singleton.port);

        return err;
}
device_initcall(srmcons_init);

/*
 * The console driver
 */
static void
srm_console_write(struct console *co, const char *s, unsigned count)
{
        unsigned long flags;

        spin_lock_irqsave(&srmcons_callback_lock, flags);
        srmcons_do_write(NULL, s, count);
        spin_unlock_irqrestore(&srmcons_callback_lock, flags);
}

static struct tty_driver *
srm_console_device(struct console *co, int *index)
{
        *index = co->index;
        return srmcons_driver;
}

static int
srm_console_setup(struct console *co, char *options)
{
        return 0;
}

static struct console srmcons = {
        .name           = "srm",
        .write          = srm_console_write,
        .device         = srm_console_device,
        .setup          = srm_console_setup,
        .flags          = CON_PRINTBUFFER | CON_BOOT,
        .index          = -1,
};

void __init
register_srm_console(void)
{
        if (!srm_is_registered_console) {
                callback_open_console();
                register_console(&srmcons);
                srm_is_registered_console = 1;
        }
}

void __init
unregister_srm_console(void)
{
        if (srm_is_registered_console) {
                callback_close_console();
                unregister_console(&srmcons);
                srm_is_registered_console = 0;
        }
}