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// SPDX-License-Identifier: GPL-2.0
/*
* n_tracerouter.c - Trace data router through tty space
*
* Copyright (C) Intel 2011
*
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* 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 <linux/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);
/**
* n_tracerouter_open() - Called when a tty is opened by a SW entity.
* @tty: terminal device to the ldisc.
*
* Return:
* 0 for success.
*
* Caveats: This should only be opened one time per SW entity.
*/
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;
}
/**
* n_tracerouter_close() - close connection
* @tty: terminal device to the ldisc.
*
* Called when a software entity wants to close a connection.
*/
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);
}
/**
* n_tracerouter_read() - read request from user space
* @tty: terminal device passed into the ldisc.
* @file: pointer to open file object.
* @buf: pointer to the data buffer that gets eventually returned.
* @nr: number of bytes of the data buffer that is returned.
*
* function that allows read() functionality in userspace. By default if this
* is not implemented it returns -EIO. This module is functioning like a
* router via n_tracerouter_receivebuf(), and there is no real requirement
* to implement this function. However, an error return value other than
* -EIO should be used just to show that there was an intent not to have
* this function implemented. Return value based on read() man pages.
*
* Return:
* -EINVAL
*/
static ssize_t n_tracerouter_read(struct tty_struct *tty, struct file *file,
unsigned char *buf, size_t nr,
void **cookie, unsigned long offset)
{
return -EINVAL;
}
/**
* n_tracerouter_write() - Function that allows write() in userspace.
* @tty: terminal device passed into the ldisc.
* @file: pointer to open file object.
* @buf: pointer to the data buffer that gets eventually returned.
* @nr: number of bytes of the data buffer that is returned.
*
* By default if this is not implemented, it returns -EIO.
* This should not be implemented, ever, because
* 1. this driver is functioning like a router via
* n_tracerouter_receivebuf()
* 2. No writes to HW will ever go through this line discpline driver.
* However, an error return value other than -EIO should be used
* just to show that there was an intent not to have this function
* implemented. Return value based on write() man pages.
*
* Return:
* -EINVAL
*/
static ssize_t n_tracerouter_write(struct tty_struct *tty, struct file *file,
const unsigned char *buf, size_t nr) {
return -EINVAL;
}
/**
* n_tracerouter_receivebuf() - Routing function for driver.
* @tty: terminal device passed into the ldisc. It's assumed
* tty will never be NULL.
* @cp: buffer, block of characters to be eventually read by
* someone, somewhere (user read() call or some kernel function).
* @fp: flag buffer.
* @count: number of characters (aka, bytes) in cp.
*
* This function takes the input buffer, cp, and passes it to
* an external API function for processing.
*/
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
};
/**
* n_tracerouter_init - module initialisation
*
* Registers this module as a line discipline driver.
*
* Return:
* 0 for success, any other value error.
*/
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;
}
/**
* n_tracerouter_exit - module unload
*
* Removes this module as a line discipline driver.
*/
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");
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