ptmx: adding handshake support

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

===================================================================

@@ -7,6 +7,8 @@
 *    -- C. Scott Ananian <[email protected]>, 14-Jan-1998
 *  Added TTY_DO_WRITE_WAKEUP to enable n_tty to send POLL_OUT to
 *      waiting writers -- Sapan Bhatia <[email protected]>
+ *  Added support for MCR/MSR, used for serial over ethernet
+ *    -- Sander van Ginkel <[email protected]>
 *
 *
 */

@@ -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;
+            }
+        return 0;
+        }          
    }

    return -ENOIOCTLCMD;