229 lines
6.6 KiB
C
229 lines
6.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* n_tracesink.c - Trace data router and sink path through tty space.
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*
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* Copyright (C) Intel 2011
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*
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* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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*
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* The trace sink uses the Linux line discipline framework to receive
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* trace data coming from the PTI source line discipline driver
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* to a user-desired tty port, like USB.
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* This is to provide a way to extract modem trace data on
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* devices that do not have a PTI HW module, or just need modem
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* trace data to come out of a different HW output port.
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* This is part of a solution for the P1149.7, compact JTAG, standard.
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*/
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/ioctl.h>
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#include <linux/tty.h>
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#include <linux/tty_ldisc.h>
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#include <linux/errno.h>
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#include <linux/string.h>
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#include <linux/bug.h>
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#include "n_tracesink.h"
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/*
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* Other ldisc drivers use 65536 which basically means,
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* 'I can always accept 64k' and flow control is off.
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* This number is deemed appropriate for this driver.
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*/
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#define RECEIVE_ROOM 65536
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#define DRIVERNAME "n_tracesink"
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/*
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* there is a quirk with this ldisc is he can write data
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* to a tty from anyone calling his kernel API, which
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* meets customer requirements in the drivers/misc/pti.c
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* project. So he needs to know when he can and cannot write when
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* the API is called. In theory, the API can be called
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* after an init() but before a successful open() which
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* would crash the system if tty is not checked.
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*/
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static struct tty_struct *this_tty;
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static DEFINE_MUTEX(writelock);
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/**
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* n_tracesink_open() - Called when a tty is opened by a SW entity.
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* @tty: terminal device to the ldisc.
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*
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* Return:
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* 0 for success,
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* -EFAULT = couldn't get a tty kref n_tracesink will sit
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* on top of
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* -EEXIST = open() called successfully once and it cannot
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* be called again.
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*
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* Caveats: open() should only be successful the first time a
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* SW entity calls it.
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*/
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static int n_tracesink_open(struct tty_struct *tty)
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{
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int retval = -EEXIST;
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mutex_lock(&writelock);
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if (this_tty == NULL) {
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this_tty = tty_kref_get(tty);
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if (this_tty == NULL) {
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retval = -EFAULT;
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} else {
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tty->disc_data = this_tty;
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tty_driver_flush_buffer(tty);
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retval = 0;
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}
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}
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mutex_unlock(&writelock);
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return retval;
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}
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/**
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* n_tracesink_close() - close connection
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* @tty: terminal device to the ldisc.
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*
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* Called when a software entity wants to close a connection.
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*/
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static void n_tracesink_close(struct tty_struct *tty)
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{
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mutex_lock(&writelock);
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tty_driver_flush_buffer(tty);
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tty_kref_put(this_tty);
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this_tty = NULL;
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tty->disc_data = NULL;
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mutex_unlock(&writelock);
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}
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/**
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* n_tracesink_read() - read request from user space
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* @tty: terminal device passed into the ldisc.
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* @file: pointer to open file object.
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* @buf: pointer to the data buffer that gets eventually returned.
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* @nr: number of bytes of the data buffer that is returned.
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*
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* function that allows read() functionality in userspace. By default if this
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* is not implemented it returns -EIO. This module is functioning like a
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* router via n_tracesink_receivebuf(), and there is no real requirement
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* to implement this function. However, an error return value other than
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* -EIO should be used just to show that there was an intent not to have
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* this function implemented. Return value based on read() man pages.
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*
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* Return:
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* -EINVAL
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*/
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static ssize_t n_tracesink_read(struct tty_struct *tty, struct file *file,
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unsigned char __user *buf, size_t nr) {
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return -EINVAL;
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}
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/**
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* n_tracesink_write() - Function that allows write() in userspace.
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* @tty: terminal device passed into the ldisc.
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* @file: pointer to open file object.
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* @buf: pointer to the data buffer that gets eventually returned.
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* @nr: number of bytes of the data buffer that is returned.
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*
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* By default if this is not implemented, it returns -EIO.
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* This should not be implemented, ever, because
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* 1. this driver is functioning like a router via
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* n_tracesink_receivebuf()
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* 2. No writes to HW will ever go through this line discpline driver.
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* However, an error return value other than -EIO should be used
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* just to show that there was an intent not to have this function
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* implemented. Return value based on write() man pages.
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*
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* Return:
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* -EINVAL
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*/
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static ssize_t n_tracesink_write(struct tty_struct *tty, struct file *file,
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const unsigned char *buf, size_t nr) {
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return -EINVAL;
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}
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/**
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* n_tracesink_datadrain() - Kernel API function used to route
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* trace debugging data to user-defined
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* port like USB.
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*
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* @buf: Trace debuging data buffer to write to tty target
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* port. Null value will return with no write occurring.
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* @count: Size of buf. Value of 0 or a negative number will
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* return with no write occuring.
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*
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* Caveat: If this line discipline does not set the tty it sits
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* on top of via an open() call, this API function will not
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* call the tty's write() call because it will have no pointer
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* to call the write().
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*/
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void n_tracesink_datadrain(u8 *buf, int count)
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{
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mutex_lock(&writelock);
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if ((buf != NULL) && (count > 0) && (this_tty != NULL))
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this_tty->ops->write(this_tty, buf, count);
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mutex_unlock(&writelock);
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}
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EXPORT_SYMBOL_GPL(n_tracesink_datadrain);
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/*
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* Flush buffer is not impelemented as the ldisc has no internal buffering
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* so the tty_driver_flush_buffer() is sufficient for this driver's needs.
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*/
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/*
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* tty_ldisc function operations for this driver.
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*/
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static struct tty_ldisc_ops tty_n_tracesink = {
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.owner = THIS_MODULE,
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.magic = TTY_LDISC_MAGIC,
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.name = DRIVERNAME,
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.open = n_tracesink_open,
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.close = n_tracesink_close,
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.read = n_tracesink_read,
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.write = n_tracesink_write
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};
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/**
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* n_tracesink_init- module initialisation
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*
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* Registers this module as a line discipline driver.
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*
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* Return:
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* 0 for success, any other value error.
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*/
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static int __init n_tracesink_init(void)
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{
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/* Note N_TRACESINK is defined in linux/tty.h */
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int retval = tty_register_ldisc(N_TRACESINK, &tty_n_tracesink);
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if (retval < 0)
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pr_err("%s: Registration failed: %d\n", __func__, retval);
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return retval;
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}
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/**
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* n_tracesink_exit - module unload
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*
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* Removes this module as a line discipline driver.
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*/
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static void __exit n_tracesink_exit(void)
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{
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int retval = tty_unregister_ldisc(N_TRACESINK);
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if (retval < 0)
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pr_err("%s: Unregistration failed: %d\n", __func__, retval);
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}
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module_init(n_tracesink_init);
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module_exit(n_tracesink_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Jay Freyensee");
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MODULE_ALIAS_LDISC(N_TRACESINK);
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MODULE_DESCRIPTION("Trace sink ldisc driver");
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