n_tracerouter and n_tracesink ldisc additions.

The n_tracerouter and n_tracesink line discpline drivers use the
Linux tty line discpline framework to route trace data coming
from a tty port (say UART for example) to the trace sink line
discipline driver and to another tty port(say USB).  Those
these two line discipline drivers can be used together,
independently from pti.c, they are part of the original
implementation solution of the MIPI P1149.7, compact JTAG, PTI
solution for Intel mobile platforms starting with the
Medfield platform.

Signed-off-by: J Freyensee <james_p_freyensee@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 238 insertions, 0 deletions

diff --git a/drivers/tty/n_tracesink.c b/drivers/tty/n_tracesink.c
new file mode 100644
index 000000000000..ddce58b973d2
--- /dev/null
+++ b/drivers/tty/n_tracesink.c
@@ -0,0 +1,238 @@
+/*
+ *  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");