linux-kernel - Re: [PATCH v2] tty: n_gsm: CR bit value should be 0 when config "initiator=0"

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Date:   Wed, 7 Jul 2021 14:08:40 +0800
From:   赵振国 <zhenguo6858@...il.com>
To:     赵振国 <zhenguo6858@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tty: n_gsm: CR bit value should be 0 when config "initiator=0"

Dear Jiri,Greg

 1:   our development board uses linux kernel , uart dev node is "/dev/ttyGS2"
 2:   config uart "/dev/ttyGS2" ,we use ngsm ldisc,and config
"c.initiator = 0;" code is as follows

  #include <stdio.h>
  #include <stdint.h>
  #include <linux/gsmmux.h>
  #include <linux/tty.h>
  #define DEFAULT_SPEED      B115200
  #define SERIAL_PORT        /dev/ttyGS2

     int ldisc = N_GSM0710;
     struct gsm_config c;
     struct termios configuration;
     uint32_t first;

     /* open the serial port */
     fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);

     /* configure the serial port : speed, flow control ... */

     /* use n_gsm line discipline */
     ioctl(fd, TIOCSETD, &ldisc);

     /* get n_gsm configuration */
     ioctl(fd, GSMIOC_GETCONF, &c);
     /* we are responter and need encoding 0 (basic) */
     c.initiator = 0;
     c.encapsulation = 0;
     /* our modem defaults to a maximum size of 127 bytes */
     c.mru = 127;
     c.mtu = 127;
    /* set the new configuration */
     ioctl(fd, GSMIOC_SETCONF, &c);
     /* get first gsmtty device node */
     ioctl(fd, GSMIOC_GETFIRST, &first);
     printf("first muxed line: /dev/gsmtty%i\n", first);

     /* and wait for ever to keep the line discipline enabled */
     daemon(0,0);
     pause();

3:  connect to ubuntu by uart serial port cable,ubuntu uart dev node
is /"dev/ttyUSB0"
send  DLC0 SABM command by "/dev/ttyUSB0",but linux development board
can't response,code is as follows

int main(int argc, char **argv)
{
    int fd;
fd = open("/dev/ttyUSB0,O_RDWR | O_NOCTTY | O_NDELAY);
char buf[256]={0xf9,0x03,0x3f,0x01,0x1c,0xf9};
write(fd,buf,6);
close(fd);
}

4:  linux development board receive data,by uart,gsm_queue will check
CR,find CR=1.so go to invalid,pls check again.
static void gsm_queue(struct gsm_mux *gsm)
{
cr ^= 1 - gsm->initiator; /* Flip so 1 always means command */
dlci = gsm->dlci[address];

switch (gsm->control) {
case SABM|PF:
if (cr == 0)
goto invalid;
if (dlci == NULL)
dlci = gsm_dlci_alloc(gsm, address);
if (dlci == NULL)
return;
if (dlci->dead)
gsm_response(gsm, address, DM);
else {
gsm_response(gsm, address, UA);
gsm_dlci_open(dlci);
}
break;