Hi Adam, > I apologize if I am mailing the wrong list; I saw the address posted > on bluez.org. > > I would like to set the CD (Carrier Detect) and RI (Ring Indicator) > signals on an rfcomm line. I understand that these are typically DCE > -> DTE signals, but in rfcomm there doesn't seem to be much meaning to > this distinction. My use case is a linux box with a bluetooth > adapter, talking to a BGB203. > > Now I see in the rfcomm driver that that tiocmset() should be able to > handle these signals: > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=net/bluetooth/rfcomm/tty.c;hb=09c7d8293a2d1317d16ef4ddb9f6dd2553d0694e > 1019 static int rfcomm_tty_tiocmset(struct tty_struct *tty, struct > file *filp, unsigned int set, unsigned int clear) > ... > 1033 if (set & TIOCM_RI) > 1034 v24_sig |= RFCOMM_V24_IC; > 1035 if (set & TIOCM_CD) > 1036 v24_sig |= RFCOMM_V24_DV; > ... > > So I tried to write code like this: > > fd = open("/dev/rfcomm1", O_RDWR | O_NDELAY); > ri = TIOCM_RI; > ioctl(fd, TIOCMSET, &ri); > > But it doesn't work. (I'm fully able to connect the rfcomm link and > pass characters over it. Moreover, I can control the DTR signal in > this manner. But not RI or CD.) > > I recompiled the net/bluetooth/rfcomm.ko driver with BT_DBG turned on, > tried setting ri to 0xffff, and saw this: > > rfcomm_tty_tiocmset: tty d25bc800 dev c34369c0 set 0xe006 clear 0x00 > > This mask is conspicuously missing the RI and CD bits (0x40 and 0x80). > This behavior seems to come from the tty driver: > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=drivers/char/tty_io.c;h=d33e5ab061779a67e63b305b30b29d01f6fe38ca;hb=HEAD > ... > 2452 static int tty_tiocmset(struct tty_struct *tty, struct file > *file, unsigned int cmd, > 2453 unsigned __user *p) > ... > 2477 set &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP; > 2478 clear &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP; > 2479 return tty->ops->tiocmset(tty, file, set, clear); > > (The mask on line 2477 comes out to 0xe006.) > > I don't know the purpose of these lines, but they seem to imply that > it is impossible to set the RI and CD signals using tiocmset() an > rfcomm device. To test my theory, I tried out this patch against my > 2.6.22 kernel: > > --- net/bluetooth/rfcomm/tty.c 2009-01-07 10:06:50.000000000 +0000 > +++ net/bluetooth/rfcomm/tty.c~ 2009-01-07 10:05:40.000000000 +0000 > @@ -1030,18 +1006,18 @@ > v24_sig |= RFCOMM_V24_RTC; > if (set & TIOCM_RTS || set & TIOCM_CTS) > v24_sig |= RFCOMM_V24_RTR; > - if (set & TIOCM_RI) > + if (set & TIOCM_OUT1) > v24_sig |= RFCOMM_V24_IC; > - if (set & TIOCM_CD) > + if (set & TIOCM_OUT2) > v24_sig |= RFCOMM_V24_DV; > > > I then changed my code snippet to use TIOCM_OUT1 instead of TIOCM_RI. > It worked perfectly, setting the Ring Indicator signal on the rfcomm > link, which was reflected on my BGB203. > > Is there any way to set RI and CD using the stock rfcomm driver? If > not, should something be changed either in net/bluetooth/rfcomm/tty.c > or in drivers/char/tty_io.c ? I don't know the purpose of TIOCM_OUT1 > / TIOCM_OUT2, but they do not seem to be used elsewhere in rfcomm, so > perhaps this remapping won't hurt anything. (If anyone has a > suggestion for a simple fix, I would be happy to try to submit a > patch, but it would be my first.) I honestly don't know why TIOCM_OUT1 etc. are working and others are not. Since this comes from the TTY subsystem, please mail LKML about it and include Alan Cox. He should know. Regards Marcel -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
