--- /dev/null
+/*
+ * n_tracesink.c - Trace data router and sink path 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.
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * The trace sink uses the Linux line discipline framework to receive
+ * trace data coming from the PTI source line discipline driver
+ * to a user-desired tty port, like USB.
+ * This is to provide a way to extract modem trace data on
+ * devices that do not have a PTI HW module, or just need modem
+ * trace data to come out of a different HW output port.
+ * 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 <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_tracesink"
+
+/*
+ * there is a quirk with this ldisc is he can write data
+ * to a tty from anyone calling his kernel API, which
+ * meets customer requirements in the drivers/misc/pti.c
+ * project. So he needs to know when he can and cannot write when
+ * the API is called. In theory, the API can be called
+ * after an init() but before a successful open() which
+ * would crash the system if tty is not checked.
+ */
+static struct tty_struct *this_tty;
+static DEFINE_MUTEX(writelock);
+
+/**
+ * n_tracesink_open() - Called when a tty is opened by a SW entity.
+ * @tty: terminal device to the ldisc.
+ *
+ * Return:
+ * 0 for success,
+ * -EFAULT = couldn't get a tty kref n_tracesink will sit
+ * on top of
+ * -EEXIST = open() called successfully once and it cannot
+ * be called again.
+ *
+ * Caveats: open() should only be successful the first time a
+ * SW entity calls it.
+ */
+static int n_tracesink_open(struct tty_struct *tty)
+{
+ int retval = -EEXIST;
+
+ mutex_lock(&writelock);
+ if (this_tty == NULL) {
+ this_tty = tty_kref_get(tty);
+ if (this_tty == NULL) {
+ retval = -EFAULT;
+ } else {
+ tty->disc_data = this_tty;
+ tty_driver_flush_buffer(tty);
+ retval = 0;
+ }
+ }
+ mutex_unlock(&writelock);
+
+ return retval;
+}
+
+/**
+ * n_tracesink_close() - close connection
+ * @tty: terminal device to the ldisc.
+ *
+ * Called when a software entity wants to close a connection.
+ */
+static void n_tracesink_close(struct tty_struct *tty)
+{
+ mutex_lock(&writelock);
+ tty_driver_flush_buffer(tty);
+ tty_kref_put(this_tty);
+ this_tty = NULL;
+ tty->disc_data = NULL;
+ mutex_unlock(&writelock);
+}
+
+/**
+ * n_tracesink_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_tracesink_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_tracesink_read(struct tty_struct *tty, struct file *file,
+ unsigned char __user *buf, size_t nr) {
+ return -EINVAL;
+}
+
+/**
+ * n_tracesink_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_tracesink_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_tracesink_write(struct tty_struct *tty, struct file *file,
+ const unsigned char *buf, size_t nr) {
+ return -EINVAL;
+}
+
+/**
+ * n_tracesink_datadrain() - Kernel API function used to route
+ * trace debugging data to user-defined
+ * port like USB.
+ *
+ * @buf: Trace debuging data buffer to write to tty target
+ * port. Null value will return with no write occurring.
+ * @count: Size of buf. Value of 0 or a negative number will
+ * return with no write occuring.
+ *
+ * Caveat: If this line discipline does not set the tty it sits
+ * on top of via an open() call, this API function will not
+ * call the tty's write() call because it will have no pointer
+ * to call the write().
+ */
+void n_tracesink_datadrain(u8 *buf, int count)
+{
+ mutex_lock(&writelock);
+
+ if ((buf != NULL) && (count > 0) && (this_tty != NULL))
+ this_tty->ops->write(this_tty, buf, count);
+
+ mutex_unlock(&writelock);
+}
+EXPORT_SYMBOL_GPL(n_tracesink_datadrain);
+
+/*
+ * 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.
+ */
+
+/*
+ * tty_ldisc function operations for this driver.
+ */
+static struct tty_ldisc_ops tty_n_tracesink = {
+ .owner = THIS_MODULE,
+ .magic = TTY_LDISC_MAGIC,
+ .name = DRIVERNAME,
+ .open = n_tracesink_open,
+ .close = n_tracesink_close,
+ .read = n_tracesink_read,
+ .write = n_tracesink_write
+};
+
+/**
+ * n_tracesink_init- module initialisation
+ *
+ * Registers this module as a line discipline driver.
+ *
+ * Return:
+ * 0 for success, any other value error.
+ */
+static int __init n_tracesink_init(void)
+{
+ /* Note N_TRACESINK is defined in linux/tty.h */
+ int retval = tty_register_ldisc(N_TRACESINK, &tty_n_tracesink);
+
+ if (retval < 0)
+ pr_err("%s: Registration failed: %d\n", __func__, retval);
+
+ return retval;
+}
+
+/**
+ * n_tracesink_exit - module unload
+ *
+ * Removes this module as a line discipline driver.
+ */
+static void __exit n_tracesink_exit(void)
+{
+ int retval = tty_unregister_ldisc(N_TRACESINK);
+
+ if (retval < 0)
+ pr_err("%s: Unregistration failed: %d\n", __func__, retval);
+}
+
+module_init(n_tracesink_init);
+module_exit(n_tracesink_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jay Freyensee");
+MODULE_ALIAS_LDISC(N_TRACESINK);
+MODULE_DESCRIPTION("Trace sink ldisc driver");
Code Review / kvmfornfv.git / blobdiff