linux-kernel - Re: [PATCH] tty: n_gsm: Fix CR bit value when initiator=0

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Date:   Wed, 16 Jun 2021 16:01:05 +0800
From:   赵振国 <zhenguo6858@...il.com>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: n_gsm: Fix CR bit value when initiator=0

Dear gregkh，Jiri

I think that linux ngsm is cp cmux function  (config
slaver,c.initiator = 0),pc side or ubuntu or terminal will send
"AT+CMUX" by tty dev, and send SABM.DISC.CLD command。

because project is YOCTO,YOCTO  is IOT open project,need config
slaver，after config “c.initiator = 0”，ngsm can‘t work normally.


slaver config ,it doesn't need to send "AT+CMUX"
----------------------------------------------------------
2.1 switch the serial line to using the n_gsm line discipline by using
    TIOCSETD ioctl.
2.2 configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl.
2.3 obtain base gsmtty number for the used serial port,

  #include <stdio.h>
  #include <stdint.h>
  #include <linux/gsmmux.h>
  #include <linux/tty.h>
  #define DEFAULT_SPEED B115200
  #define SERIAL_PORT   /dev/ttyS0

    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();


2021-06-16 15:45 GMT+08:00, Jiri Slaby <jirislaby@...nel.org>:
> On 16. 06. 21, 9:39, Greg KH wrote:
>>
>> A: http://en.wikipedia.org/wiki/Top_post
>> Q: Were do I find info about this thing called top-posting?
>> A: Because it messes up the order in which people normally read text.
>> Q: Why is top-posting such a bad thing?
>> A: Top-posting.
>> Q: What is the most annoying thing in e-mail?
>>
>> A: No.
>> Q: Should I include quotations after my reply?
>>
>> http://daringfireball.net/2007/07/on_top
>>
>> On Wed, Jun 16, 2021 at 03:29:11PM +0800, 赵振国 wrote:
>>> Dear gregkh
>>>
>>> 1:  Documentation/driver-api/serial/n_gsm.rst
>>>
>>> The text introduces the config of master ( c.initiator = 1), but the
>>> config of as responder is different.
>>> when set gsm->initiator=0 by GSMIOC_SETCONF ,ngsm driver should be
>>> responder(slaver)
>>>
>>> config：
>>> 	c.initiator = 0;    // set initiator=0，ngsm as responder
>>> 	ioctl(fd, GSMIOC_SETCONF, &c);
>>>
>>> 2:  if master side send SABM/DISC frame data by uart dev
>>>      DLC0 control data frame:f9 03 3f 01 1c f9
>>>      kernel log： gsmld_receive: 00000000: f9 03 3f 01 1c f9
>>>
>>> {
>>> 	cr = gsm->address & 1;		/* C/R bit */
>>> //CR value=1
>>>
>>> 	gsm_print_packet("<--", address, cr, gsm->control, gsm->buf, gsm->len);
>>>
>>> 	cr ^= 1 - gsm->initiator;	/* Flip so 1 always means command */
>>> //when gsm->initiator is 0, CR value=0 by "^=" calculation
>>> 	dlci = gsm->dlci[address];
>>>
>>> 	switch (gsm->control) {
>>> 	case SABM|PF:
>>> 		if (cr == 0)
>>> 			goto invalid;                       //if CR value=0,ngsm will goto
>>> invalid,but the dlc0 control frame data is right,if we can't modify
>>> ,ngsm can't send UA response data
>>> }
>>
>> I am sorry, but I really do not understand what you are saying here.
>> Please resubmit your patch with an updated changelog that explains why
>> this change is needed and what it does.
>
> And why it was able to work until now. I.e. isn't the Documentation wrong?
>
> thanks,
> --
> js
> suse labs
>