[plug] Any kernel hackers out there...?

[Kim Covil]

Hi,

Is there anyone on the list who might be able to give me some hints on
how to talk to a serial device from within a 2.2 kernel...?

I have a device running a 2.2 kernel on a strongarm processor. The
kernel is not modular (and is quite highly modified). There is a serial
device I would like to query on boot to determine whether it is attached
and what id it returns, and then set a variable within the kernel before
it carries on with the rest of its boot sequence. The initialisation
sequence is pretty simple, so I just need to know how to send a few
bytes to the device and read back a few bytes in reply with a timeout in
case the device is not attached.

At the moment I have some userspace code to do this via /dev/ttyS0 and I
set the kernel variable via an ioctl, but I would like to be able to do
the same thing from within the kernel itself to save having to put the
user space program on the filesystem and have the filesystem mounted
before the code is called.

Currently my rough scratching around looking for example code has come
up with something like the code at the bottom. But I have no idea
whether this is in anyway correct, and I can't find any examples on how
I read 3 bytes from the serial device. Also I have been told I should
wrap the code in a busy-wait but I am not sure about that one either.

Any help would be appreciated,

Cheers

Kim


#include <linux/tty.h>
static int /* detect the presence of a tuner module and return its id */
tuner_detect ()
{
   int ret;
   char buf[5];
   char init_data[3] = { 0x01, 0x00, 0x01 };
   struct async_struct *info = IRQ_ports[15]; /* tuner on ttyS0 */
   struct tty_struct *tty = info->tty;
   tty->termios->c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|
INLCR|IGNCR|ICRNL|IXON);
   tty->termios->c_oflag &= ~OPOST;
   tty->termios->c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
   tty->termios->c_cflag &= ~(CSIZE|PARENB);
   tty->termios->c_cflag |= CS8;
   tty->termios->c_iflag |= B19200;
   tty->termios->c_oflag |= B19200;

   if ( tty->driver.write(tty, 0, init_data, 3) < 3 ) {
      /* failed to send data to the tuner */
      return -1;
   }


   /*
    * here's where I want to read 3 bytes from the tty... 
    * with a timeout in case the tuner doesn't exist and therefore
    * doesn't reply
    */


   return ret;
}

-- 
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Kim Covil - CSIRO Exploration & Mining  E-mail:  kim.covil at csiro.au 
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            PO Box 1130, Bentley,       Direct:  +61 8 6436 8638    /   
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        Please direct all personal e-mail to kimbotha at covil.com.au