[PATCH] ptmx: adding handshake support

sander van ginkel
2008-03-11T21:15:50Z

For serial over ethernet communication, /dev/ptmx will be used to create
a virtual device.
Due to the lack of a modem status register and a modem control register
in the ptmx driver,
it won't be possible to transfer handshake signaling.

I wrote this patch to add these registers to the ptmx driver.
The modem status register, which controls CD,CTS,DSR,RI is normally
read-only. To be able to
pass these signals from the remote port to the local ptmx device, I've
added an IOCTL routine.
The result of a remote TIOCMGET IOCTL call , can be passed directly
through this IOCTL routine.
The IOCTL value I used for this is, 0x5426 which was formerly known as
TIOCTTYGSTRUCT.

I've tested this patch at an 2.6.16.27 kernel.

Suggestions and/or other test results are welcome.

Sander

Signed-off-by: Sander van Ginkel <sander@van-ginkel.eu>

===================================================================
--- drivers/char/pty.c 2008-03-03 20:02:09.000000000 +0100
+++ drivers/char/pty-new.c 2008-03-02 21:55:53.000000000 +0100
@@ -7,6 +7,8 @@
* -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
* Added TTY_DO_WRITE_WAKEUP to enable n_tty to send POLL_OUT to
* waiting writers -- Sapan Bhatia <sapan@corewars.org>
+ * Added support for MCR/MSR, used for serial over ethernet
+ * -- Sander van Ginkel <sander@van-ginkel.eu>
*
*
*/
@@ -32,6 +34,16 @@
#include <linux/bitops.h>
#include <linux/devpts_fs.h>

+struct pty_mcrmsr {
+
+ struct semaphore sem; /* locks this structure */
+
+ /* for tiocmget and tiocmset functions */
+
+ int msr; /* MSR shadow */
+ int mcr; /* MCR shadow */
+};
+
/* These are global because they are accessed in tty_io.c */
#ifdef CONFIG_UNIX98_PTYS
struct tty_driver *ptm_driver;
@@ -199,6 +211,7 @@

static int pty_open(struct tty_struct *tty, struct file * filp)
{
+ struct pty_mcrmsr *mcrmsr;
int retval = -ENODEV;

if (!tty || !tty->link)
@@ -216,10 +229,90 @@
set_bit(TTY_THROTTLED, &tty->flags);
set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
retval = 0;
+
+ /* initialize the pointer in case something fails */
+
+ tty->driver_data = NULL;
+ tty->link->driver_data = NULL;
+
+ /* first time accessing this device, let's create it */
+
+ mcrmsr = kmalloc(sizeof(*mcrmsr), GFP_KERNEL);
+
+ init_MUTEX(&mcrmsr->sem);
+
+ if (mcrmsr != NULL) {
+ down(&mcrmsr->sem);
+
+ /* save our structure within the tty structure */
+
+ mcrmsr->mcr=0;
+ mcrmsr->msr=0;
+
+ tty->driver_data = mcrmsr;
+ tty->link->driver_data = mcrmsr;
+
+ up(&mcrmsr->sem);
+
+ }
+
out:
return retval;
}

+static int pty_tiocmget(struct tty_struct *tty, struct file *file)
+{
+ struct pty_mcrmsr *mcrmsr = tty->driver_data;
+ unsigned int result = 0;
+ unsigned int msr=0;
+ unsigned int mcr=0;
+
+ if (tty->driver_data != NULL) {
+ msr = mcrmsr->msr;
+ mcr = mcrmsr->mcr;
+ }
+
+ result = ((mcr & 0x01) ? TIOCM_DTR : 0) | /* DTR is set */
+ ((mcr & 0x02) ? TIOCM_RTS : 0) | /* RTS is set */
+ ((mcr & 0x04) ? TIOCM_LOOP : 0) | /* LOOP is set */
+ ((msr & 0x08) ? TIOCM_CTS : 0) | /* CTS is set */
+ ((msr & 0x10) ? TIOCM_CAR : 0) | /* Carrier detect is set*/
+ ((msr & 0x20) ? TIOCM_RI : 0) | /* Ring Indicator is set */
+ ((msr & 0x40) ? TIOCM_DSR : 0); /* DSR is set */
+
+ return result;
+}
+
+static int pty_tiocmset(struct tty_struct *tty, struct file
*file,unsigned int set, unsigned int clear)
+{
+ struct pty_mcrmsr *mcrmsr = tty->driver_data;
+ unsigned int mcr=0;
+
+ if (tty->driver_data != NULL)
+ mcr = mcrmsr->mcr;
+
+ if (set & TIOCM_DTR)
+ mcr |= 0x01;
+ if (set & TIOCM_RTS)
+ mcr |= 0x02;
+ if (set & TIOCM_LOOP)
+ mcr |= 0x04;
+
+ if (clear & TIOCM_DTR)
+ mcr &= ~0x01;
+ if (clear & TIOCM_RTS)
+ mcr &= ~0x02;
+ if (clear & TIOCM_LOOP)
+ mcr &= ~0x04;
+
+ /* set the new MCR value in the device */
+
+ if (tty->driver_data != NULL)
+ mcrmsr->mcr=mcr;
+
+ return 0;
+}
+
static void pty_set_termios(struct tty_struct *tty, struct termios
*old_termios)
{
tty->termios->c_cflag &= ~(CSIZE | PARENB);
@@ -235,6 +328,8 @@
.chars_in_buffer = pty_chars_in_buffer,
.unthrottle = pty_unthrottle,
.set_termios = pty_set_termios,
+ .tiocmget = pty_tiocmget,
+ .tiocmset = pty_tiocmset,
};

/* Traditional BSD devices */
@@ -339,11 +434,44 @@
static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg)
{
+ unsigned int value;
+ struct pty_mcrmsr *mcrmsr = tty->driver_data;
+ unsigned int msr=0;
+ unsigned int mcr=0;
+
switch (cmd) {
case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
return pty_set_lock(tty, (int __user *)arg);
case TIOCGPTN: /* Get PT Number */
return put_user(tty->index, (unsigned int __user *)arg);
+
+ case 0x5426: /* Set all of the handshake line, even the normally
read only */
+ {
+ if (copy_from_user(&value,(unsigned int *)arg,sizeof(unsigned
int)))
+ return -EFAULT;
+
+ if (value & 0x0002) /* DTR set */
+ mcr|=0x01;
+ if (value & 0x0004) /* RTS set */
+ mcr|=0x02;
+ if (value & 0x8000) /* LOOP set */
+ mcr|=0x04;
+ if (value & 0x0020) /* CTS set */
+ msr|=0x08;
+ if (value & 0x0040) /* DCD set */
+ msr|=0x10;
+ if (value & 0x0080) /* RI set */
+ msr|=0x20;
+ if (value & 0x0100) /* DSR set */
+ msr|=0x40;
+
+ if (tty->driver_data != NULL)
+ {
+ mcrmsr->msr=msr;
+ mcrmsr->mcr=mcr;