/*
 *  dashtty.c - tty driver for Dash channels interface.
 *
 *  Copyright (C) 2007,2008,2012 Imagination Technologies
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file COPYING in the main directory of this archive
 * for more details.
 *
 */

#include <linux/atomic.h>
#include <linux/completion.h>
#include <linux/console.h>
#include <linux/delay.h>
#include <linux/export.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kthread.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/serial.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/timer.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/uaccess.h>

#include <asm/da.h>

/* Channel error codes */
#define CONAOK  0
#define CONERR  1
#define CONBAD  2
#define CONPRM  3
#define CONADR  4
#define CONCNT  5
#define CONCBF  6
#define CONCBE  7
#define CONBSY  8

/* Default channel for the console */
#define CONSOLE_CHANNEL      1

#define NUM_TTY_CHANNELS     6

/* Auto allocate */
#define DA_TTY_MAJOR        0

/* A speedy poll rate helps the userland debug process connection response.
 * But, if you set it too high then no other userland processes get much
 * of a look in.
 */
#define DA_TTY_POLL (HZ / 50)

/*
 * A short put delay improves latency but has a high throughput overhead
 */
#define DA_TTY_PUT_DELAY (HZ / 100)

static atomic_t num_channels_need_poll = ATOMIC_INIT(0);

static struct timer_list poll_timer;

static struct tty_driver *channel_driver;

static struct timer_list put_timer;
static struct task_struct *dashtty_thread;

#define RX_BUF_SIZE 1024

enum {
        INCHR = 1,
        OUTCHR,
        RDBUF,
        WRBUF,
        RDSTAT
};

/**
 * struct dashtty_port - Wrapper struct for dashtty tty_port.
 * @port:               TTY port data
 * @rx_lock:            Lock for rx_buf.
 *                      This protects between the poll timer and user context.
 *                      It's also held during read SWITCH operations.
 * @rx_buf:             Read buffer
 * @xmit_lock:          Lock for xmit_*, and port.xmit_buf.
 *                      This protects between user context and kernel thread.
 *                      It's also held during write SWITCH operations.
 * @xmit_cnt:           Size of xmit buffer contents
 * @xmit_head:          Head of xmit buffer where data is written
 * @xmit_tail:          Tail of xmit buffer where data is read
 * @xmit_empty:         Completion for xmit buffer being empty
 */
struct dashtty_port {
        struct tty_port          port;
        spinlock_t               rx_lock;
        void                    *rx_buf;
        struct mutex             xmit_lock;
        unsigned int             xmit_cnt;
        unsigned int             xmit_head;
        unsigned int             xmit_tail;
        struct completion        xmit_empty;
};

static struct dashtty_port dashtty_ports[NUM_TTY_CHANNELS];

static atomic_t dashtty_xmit_cnt = ATOMIC_INIT(0);
static wait_queue_head_t dashtty_waitqueue;

/*
 * Low-level DA channel access routines
 */
static int chancall(int in_bios_function, int in_channel,
                    int in_arg2, void *in_arg3,
                    void *in_arg4)
{
        register int   bios_function asm("D1Ar1") = in_bios_function;
        register int   channel       asm("D0Ar2") = in_channel;
        register int   arg2          asm("D1Ar3") = in_arg2;
        register void *arg3          asm("D0Ar4") = in_arg3;
        register void *arg4          asm("D1Ar5") = in_arg4;
        register int   bios_call     asm("D0Ar6") = 3;
        register int   result        asm("D0Re0");

        asm volatile (
                "MSETL  [A0StP++], %6,%4,%2\n\t"
                "ADD    A0StP, A0StP, #8\n\t"
                "SWITCH #0x0C30208\n\t"
                "GETD   %0, [A0StP+#-8]\n\t"
                "SUB    A0StP, A0StP, #(4*6)+8\n\t"
                : "=d" (result)   /* outs */
                : "d" (bios_function),
                  "d" (channel),
                  "d" (arg2),
                  "d" (arg3),
                  "d" (arg4),
                  "d" (bios_call) /* ins */
                : "memory");

        return result;
}

/*
 * Attempts to fetch count bytes from channel and returns actual count.
 */
static int fetch_data(unsigned int channel)
{
        struct dashtty_port *dport = &dashtty_ports[channel];
        int received = 0;

        spin_lock_bh(&dport->rx_lock);
        /* check the port isn't being shut down */
        if (!dport->rx_buf)
                goto unlock;
        if (chancall(RDBUF, channel, RX_BUF_SIZE,
                     (void *)dport->rx_buf, &received) == CONAOK) {
                if (received) {
                        int space;
                        unsigned char *cbuf;

                        space = tty_prepare_flip_string(&dport->port, &cbuf,
                                                        received);

                        if (space <= 0)
                                goto unlock;

                        memcpy(cbuf, dport->rx_buf, space);
                        tty_flip_buffer_push(&dport->port);
                }
        }
unlock:
        spin_unlock_bh(&dport->rx_lock);

        return received;
}

/**
 * find_channel_to_poll() - Returns number of the next channel to poll.
 * Returns:     The number of the next channel to poll, or -1 if none need
 *              polling.
 */
static int find_channel_to_poll(void)
{
        static int last_polled_channel;
        int last = last_polled_channel;
        int chan;
        struct dashtty_port *dport;

        for (chan = last + 1; ; ++chan) {
                if (chan >= NUM_TTY_CHANNELS)
                        chan = 0;

                dport = &dashtty_ports[chan];
                if (dport->rx_buf) {
                        last_polled_channel = chan;
                        return chan;
                }

                if (chan == last)
                        break;
        }
        return -1;
}

/**
 * put_channel_data() - Write out a block of channel data.
 * @chan:       DA channel number.
 *
 * Write a single block of data out to the debug adapter. If the circular buffer
 * is wrapped then only the first block is written.
 *
 * Returns:     1 if the remote buffer was too full to accept data.
 *              0 otherwise.
 */
static int put_channel_data(unsigned int chan)
{
        struct dashtty_port *dport;
        struct tty_struct *tty;
        int number_written;
        unsigned int count = 0;

        dport = &dashtty_ports[chan];
        mutex_lock(&dport->xmit_lock);
        if (dport->xmit_cnt) {
                count = min((unsigned int)(SERIAL_XMIT_SIZE - dport->xmit_tail),
                            dport->xmit_cnt);
                chancall(WRBUF, chan, count,
                         dport->port.xmit_buf + dport->xmit_tail,
                         &number_written);
                dport->xmit_cnt -= number_written;
                if (!dport->xmit_cnt) {
                        /* reset pointers to avoid wraps */
                        dport->xmit_head = 0;
                        dport->xmit_tail = 0;
                        complete(&dport->xmit_empty);
                } else {
                        dport->xmit_tail += number_written;
                        if (dport->xmit_tail >= SERIAL_XMIT_SIZE)
                                dport->xmit_tail -= SERIAL_XMIT_SIZE;
                }
                atomic_sub(number_written, &dashtty_xmit_cnt);
        }
        mutex_unlock(&dport->xmit_lock);

        /* if we've made more data available, wake up tty */
        if (count && number_written) {
                tty = tty_port_tty_get(&dport->port);
                if (tty) {
                        tty_wakeup(tty);
                        tty_kref_put(tty);
                }
        }

        /* did the write fail? */
        return count && !number_written;
}

/**
 * put_data() - Kernel thread to write out blocks of channel data to DA.
 * @arg:        Unused.
 *
 * This kernel thread runs while @dashtty_xmit_cnt != 0, and loops over the
 * channels to write out any buffered data. If any of the channels stall due to
 * the remote buffer being full, a hold off happens to allow the debugger to
 * drain the buffer.
 */
static int put_data(void *arg)
{
        unsigned int chan, stall;

        __set_current_state(TASK_RUNNING);
        while (!kthread_should_stop()) {
                /*
                 * For each channel see if there's anything to transmit in the
                 * port's xmit_buf.
                 */
                stall = 0;
                for (chan = 0; chan < NUM_TTY_CHANNELS; ++chan)
                        stall += put_channel_data(chan);

                /*
                 * If some of the buffers are full, hold off for a short while
                 * to allow them to empty.
                 */
                if (stall)
                        msleep(25);

                wait_event_interruptible(dashtty_waitqueue,
                                         atomic_read(&dashtty_xmit_cnt));
        }

        return 0;
}

/*
 *      This gets called every DA_TTY_POLL and polls the channels for data
 */
static void dashtty_timer(unsigned long ignored)
{
        int channel;

        /* If there are no ports open do nothing and don't poll again. */
        if (!atomic_read(&num_channels_need_poll))
                return;

        channel = find_channel_to_poll();

        /* Did we find a channel to poll? */
        if (channel >= 0)
                fetch_data(channel);

        mod_timer_pinned(&poll_timer, jiffies + DA_TTY_POLL);
}

static void add_poll_timer(struct timer_list *poll_timer)
{
        setup_timer(poll_timer, dashtty_timer, 0);
        poll_timer->expires = jiffies + DA_TTY_POLL;

        /*
         * Always attach the timer to the boot CPU. The DA channels are per-CPU
         * so all polling should be from a single CPU.
         */
        add_timer_on(poll_timer, 0);
}

static int dashtty_port_activate(struct tty_port *port, struct tty_struct *tty)
{
        struct dashtty_port *dport = container_of(port, struct dashtty_port,
                                                  port);
        void *rx_buf;

        /* Allocate the buffer we use for writing data */
        if (tty_port_alloc_xmit_buf(port) < 0)
                goto err;

        /* Allocate the buffer we use for reading data */
        rx_buf = kzalloc(RX_BUF_SIZE, GFP_KERNEL);
        if (!rx_buf)
                goto err_free_xmit;

        spin_lock_bh(&dport->rx_lock);
        dport->rx_buf = rx_buf;
        spin_unlock_bh(&dport->rx_lock);

        /*
         * Don't add the poll timer if we're opening a console. This
         * avoids the overhead of polling the Dash but means it is not
         * possible to have a login on /dev/console.
         *
         */
        if (dport != &dashtty_ports[CONSOLE_CHANNEL])
                if (atomic_inc_return(&num_channels_need_poll) == 1)
                        add_poll_timer(&poll_timer);

        return 0;
err_free_xmit:
        tty_port_free_xmit_buf(port);
err:
        return -ENOMEM;
}

static void dashtty_port_shutdown(struct tty_port *port)
{
        struct dashtty_port *dport = container_of(port, struct dashtty_port,
                                                  port);
        void *rx_buf;
        unsigned int count;

        /* stop reading */
        if (dport != &dashtty_ports[CONSOLE_CHANNEL])
                if (atomic_dec_and_test(&num_channels_need_poll))
                        del_timer_sync(&poll_timer);

        mutex_lock(&dport->xmit_lock);
        count = dport->xmit_cnt;
        mutex_unlock(&dport->xmit_lock);
        if (count) {
                /*
                 * There's still data to write out, so wake and wait for the
                 * writer thread to drain the buffer.
                 */
                del_timer(&put_timer);
                wake_up_interruptible(&dashtty_waitqueue);
                wait_for_completion(&dport->xmit_empty);
        }

        /* Null the read buffer (timer could still be running!) */
        spin_lock_bh(&dport->rx_lock);
        rx_buf = dport->rx_buf;
        dport->rx_buf = NULL;
        spin_unlock_bh(&dport->rx_lock);
        /* Free the read buffer */
        kfree(rx_buf);

        /* Free the write buffer */
        tty_port_free_xmit_buf(port);
}

static const struct tty_port_operations dashtty_port_ops = {
        .activate       = dashtty_port_activate,
        .shutdown       = dashtty_port_shutdown,
};

static int dashtty_install(struct tty_driver *driver, struct tty_struct *tty)
{
        return tty_port_install(&dashtty_ports[tty->index].port, driver, tty);
}

static int dashtty_open(struct tty_struct *tty, struct file *filp)
{
        return tty_port_open(tty->port, tty, filp);
}

static void dashtty_close(struct tty_struct *tty, struct file *filp)
{
        return tty_port_close(tty->port, tty, filp);
}

static void dashtty_hangup(struct tty_struct *tty)
{
        int channel;
        struct dashtty_port *dport;

        channel = tty->index;
        dport = &dashtty_ports[channel];

        /* drop any data in the xmit buffer */
        mutex_lock(&dport->xmit_lock);
        if (dport->xmit_cnt) {
                atomic_sub(dport->xmit_cnt, &dashtty_xmit_cnt);
                dport->xmit_cnt = 0;
                dport->xmit_head = 0;
                dport->xmit_tail = 0;
                complete(&dport->xmit_empty);
        }
        mutex_unlock(&dport->xmit_lock);

        tty_port_hangup(tty->port);
}

/**
 * dashtty_put_timer() - Delayed wake up of kernel thread.
 * @ignored:    unused
 *
 * This timer function wakes up the kernel thread if any data exists in the
 * buffers. It is used to delay the expensive writeout until the writer has
 * stopped writing.
 */
static void dashtty_put_timer(unsigned long ignored)
{
        if (atomic_read(&dashtty_xmit_cnt))
                wake_up_interruptible(&dashtty_waitqueue);
}

static int dashtty_write(struct tty_struct *tty, const unsigned char *buf,
                         int total)
{
        int channel, count, block;
        struct dashtty_port *dport;

        /* Determine the channel */
        channel = tty->index;
        dport = &dashtty_ports[channel];

        /*
         * Write to output buffer.
         *
         * The reason that we asynchronously write the buffer is because if we
         * were to write the buffer synchronously then because DA channels are
         * per-CPU the buffer would be written to the channel of whatever CPU
         * we're running on.
         *
         * What we actually want to happen is have all input and output done on
         * one CPU.
         */
        mutex_lock(&dport->xmit_lock);
        /* work out how many bytes we can write to the xmit buffer */
        total = min(total, (int)(SERIAL_XMIT_SIZE - dport->xmit_cnt));
        atomic_add(total, &dashtty_xmit_cnt);
        dport->xmit_cnt += total;
        /* write the actual bytes (may need splitting if it wraps) */
        for (count = total; count; count -= block) {
                block = min(count, (int)(SERIAL_XMIT_SIZE - dport->xmit_head));
                memcpy(dport->port.xmit_buf + dport->xmit_head, buf, block);
                dport->xmit_head += block;
                if (dport->xmit_head >= SERIAL_XMIT_SIZE)
                        dport->xmit_head -= SERIAL_XMIT_SIZE;
                buf += block;
        }
        count = dport->xmit_cnt;
        /* xmit buffer no longer empty? */
        if (count)
                reinit_completion(&dport->xmit_empty);
        mutex_unlock(&dport->xmit_lock);

        if (total) {
                /*
                 * If the buffer is full, wake up the kthread, otherwise allow
                 * some more time for the buffer to fill up a bit before waking
                 * it.
                 */
                if (count == SERIAL_XMIT_SIZE) {
                        del_timer(&put_timer);
                        wake_up_interruptible(&dashtty_waitqueue);
                } else {
                        mod_timer(&put_timer, jiffies + DA_TTY_PUT_DELAY);
                }
        }
        return total;
}

static int dashtty_write_room(struct tty_struct *tty)
{
        struct dashtty_port *dport;
        int channel;
        int room;

        channel = tty->index;
        dport = &dashtty_ports[channel];

        /* report the space in the xmit buffer */
        mutex_lock(&dport->xmit_lock);
        room = SERIAL_XMIT_SIZE - dport->xmit_cnt;
        mutex_unlock(&dport->xmit_lock);

        return room;
}

static int dashtty_chars_in_buffer(struct tty_struct *tty)
{
        struct dashtty_port *dport;
        int channel;
        int chars;

        channel = tty->index;
        dport = &dashtty_ports[channel];

        /* report the number of bytes in the xmit buffer */
        mutex_lock(&dport->xmit_lock);
        chars = dport->xmit_cnt;
        mutex_unlock(&dport->xmit_lock);

        return chars;
}

static const struct tty_operations dashtty_ops = {
        .install                = dashtty_install,
        .open                   = dashtty_open,
        .close                  = dashtty_close,
        .hangup                 = dashtty_hangup,
        .write                  = dashtty_write,
        .write_room             = dashtty_write_room,
        .chars_in_buffer        = dashtty_chars_in_buffer,
};

static int __init dashtty_init(void)
{
        int ret;
        int nport;
        struct dashtty_port *dport;

        if (!metag_da_enabled())
                return -ENODEV;

        channel_driver = tty_alloc_driver(NUM_TTY_CHANNELS,
                                          TTY_DRIVER_REAL_RAW);
        if (IS_ERR(channel_driver))
                return PTR_ERR(channel_driver);

        channel_driver->driver_name = "metag_da";
        channel_driver->name = "ttyDA";
        channel_driver->major = DA_TTY_MAJOR;
        channel_driver->minor_start = 0;
        channel_driver->type = TTY_DRIVER_TYPE_SERIAL;
        channel_driver->subtype = SERIAL_TYPE_NORMAL;
        channel_driver->init_termios = tty_std_termios;
        channel_driver->init_termios.c_cflag |= CLOCAL;

        tty_set_operations(channel_driver, &dashtty_ops);
        for (nport = 0; nport < NUM_TTY_CHANNELS; nport++) {
                dport = &dashtty_ports[nport];
                tty_port_init(&dport->port);
                dport->port.ops = &dashtty_port_ops;
                spin_lock_init(&dport->rx_lock);
                mutex_init(&dport->xmit_lock);
                /* the xmit buffer starts empty, i.e. completely written */
                init_completion(&dport->xmit_empty);
                complete(&dport->xmit_empty);
        }

        setup_timer(&put_timer, dashtty_put_timer, 0);

        init_waitqueue_head(&dashtty_waitqueue);
        dashtty_thread = kthread_create(put_data, NULL, "ttyDA");
        if (IS_ERR(dashtty_thread)) {
                pr_err("Couldn't create dashtty thread\n");
                ret = PTR_ERR(dashtty_thread);
                goto err_destroy_ports;
        }
        /*
         * Bind the writer thread to the boot CPU so it can't migrate.
         * DA channels are per-CPU and we want all channel I/O to be on a single
         * predictable CPU.
         */
        kthread_bind(dashtty_thread, 0);
        wake_up_process(dashtty_thread);

        ret = tty_register_driver(channel_driver);

        if (ret < 0) {
                pr_err("Couldn't install dashtty driver: err %d\n",
                       ret);
                goto err_stop_kthread;
        }

        return 0;

err_stop_kthread:
        kthread_stop(dashtty_thread);
err_destroy_ports:
        for (nport = 0; nport < NUM_TTY_CHANNELS; nport++) {
                dport = &dashtty_ports[nport];
                tty_port_destroy(&dport->port);
        }
        put_tty_driver(channel_driver);
        return ret;
}

static void dashtty_exit(void)
{
        int nport;
        struct dashtty_port *dport;

        del_timer_sync(&put_timer);
        kthread_stop(dashtty_thread);
        del_timer_sync(&poll_timer);
        tty_unregister_driver(channel_driver);
        for (nport = 0; nport < NUM_TTY_CHANNELS; nport++) {
                dport = &dashtty_ports[nport];
                tty_port_destroy(&dport->port);
        }
        put_tty_driver(channel_driver);
}

module_init(dashtty_init);
module_exit(dashtty_exit);

#ifdef CONFIG_DA_CONSOLE

static void dash_console_write(struct console *co, const char *s,
                               unsigned int count)
{
        int actually_written;

        chancall(WRBUF, CONSOLE_CHANNEL, count, (void *)s, &actually_written);
}

static struct tty_driver *dash_console_device(struct console *c, int *index)
{
        *index = c->index;
        return channel_driver;
}

struct console dash_console = {
        .name = "ttyDA",
        .write = dash_console_write,
        .device = dash_console_device,
        .flags = CON_PRINTBUFFER,
        .index = 1,
};

#endif