n_tracerouter.c

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/*
 *  n_tracerouter.c - Trace data router through tty space
 *
 *  Copyright (C) Intel 2011
 *
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * This trace router uses the Linux line discipline framework to route
 * trace data coming from a HW Modem to a PTI (Parallel Trace Module) port.
 * The solution is not specific to a HW modem and this line disciple can
 * be used to route any stream of data in kernel space.
 * This is part of a solution for the P1149.7, compact JTAG, standard.
 */

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/ioctl.h>
#include <linux/tty.h>
#include <linux/tty_ldisc.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <asm-generic/bug.h>
#include "n_tracesink.h"

/*
 * Other ldisc drivers use 65536 which basically means,
 * 'I can always accept 64k' and flow control is off.
 * This number is deemed appropriate for this driver.
 */
#define RECEIVE_ROOM    65536
#define DRIVERNAME  "n_tracerouter"

/*
 * struct to hold private configuration data for this ldisc.
 * opencalled is used to hold if this ldisc has been opened.
 * kref_tty holds the tty reference the ldisc sits on top of.
 */
struct tracerouter_data {
    u8 opencalled;
    struct tty_struct *kref_tty;
};
static struct tracerouter_data *tr_data;

/* lock for when tty reference is being used */
static DEFINE_MUTEX(routelock);

static int n_tracerouter_open(struct tty_struct *tty)
{
    int retval = -EEXIST;

    mutex_lock(&routelock);
    if (tr_data->opencalled == 0) {

        tr_data->kref_tty = tty_kref_get(tty);
        if (tr_data->kref_tty == NULL) {
            retval = -EFAULT;
        } else {
            tr_data->opencalled = 1;
            tty->disc_data      = tr_data;
            tty->receive_room   = RECEIVE_ROOM;
            tty_driver_flush_buffer(tty);
            retval = 0;
        }
    }
    mutex_unlock(&routelock);
    return retval;
}

static void n_tracerouter_close(struct tty_struct *tty)
{
    struct tracerouter_data *tptr = tty->disc_data;

    mutex_lock(&routelock);
    WARN_ON(tptr->kref_tty != tr_data->kref_tty);
    tty_driver_flush_buffer(tty);
    tty_kref_put(tr_data->kref_tty);
    tr_data->kref_tty = NULL;
    tr_data->opencalled = 0;
    tty->disc_data = NULL;
    mutex_unlock(&routelock);
}

static ssize_t n_tracerouter_read(struct tty_struct *tty, struct file *file,
                  unsigned char __user *buf, size_t nr) {
    return -EINVAL;
}

static ssize_t n_tracerouter_write(struct tty_struct *tty, struct file *file,
                   const unsigned char *buf, size_t nr) {
    return -EINVAL;
}

static void n_tracerouter_receivebuf(struct tty_struct *tty,
                    const unsigned char *cp,
                    char *fp, int count)
{
    mutex_lock(&routelock);
    n_tracesink_datadrain((u8 *) cp, count);
    mutex_unlock(&routelock);
}

/*
 * Flush buffer is not impelemented as the ldisc has no internal buffering
 * so the tty_driver_flush_buffer() is sufficient for this driver's needs.
 */

static struct tty_ldisc_ops tty_ptirouter_ldisc = {
    .owner      = THIS_MODULE,
    .magic      = TTY_LDISC_MAGIC,
    .name       = DRIVERNAME,
    .open       = n_tracerouter_open,
    .close      = n_tracerouter_close,
    .read       = n_tracerouter_read,
    .write      = n_tracerouter_write,
    .receive_buf    = n_tracerouter_receivebuf
};

static int __init n_tracerouter_init(void)
{
    int retval;

    tr_data = kzalloc(sizeof(struct tracerouter_data), GFP_KERNEL);
    if (tr_data == NULL)
        return -ENOMEM;


    /* Note N_TRACEROUTER is defined in linux/tty.h */
    retval = tty_register_ldisc(N_TRACEROUTER, &tty_ptirouter_ldisc);
    if (retval < 0) {
        pr_err("%s: Registration failed: %d\n", __func__, retval);
        kfree(tr_data);
    }
    return retval;
}

static void __exit n_tracerouter_exit(void)
{
    int retval = tty_unregister_ldisc(N_TRACEROUTER);

    if (retval < 0)
        pr_err("%s: Unregistration failed: %d\n", __func__,  retval);
    else
        kfree(tr_data);
}

module_init(n_tracerouter_init);
module_exit(n_tracerouter_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Jay Freyensee");
MODULE_ALIAS_LDISC(N_TRACEROUTER);
MODULE_DESCRIPTION("Trace router ldisc driver");