On Wed, Apr 11, 2018 at 11:10:22AM +0200, Uwe Kleine-König wrote: > Hello, > > I have the following setup: > > - arm/imx6 based machine > - null-modem cable between two uart ports (driver: imx.c) > - tested with 4.9 and 4.16 > > To test handshaking signals port A's DTR signal is toggled using > TIOCMSET and then port B's DCD and DSR is read to check if the new level > is readable there. > > The problem I'm faced now is that this fails sometimes[1] because when A's > DTR is set inactive the level on B's DCD changes (as expected) and the > driver calls uart_handle_dcd_change(0) which results in tty_hangup(tty) > for B. Then when calling ioctl(fd_B, TIOCMGET, ..) the command is > handled in hung_up_tty_ioctl() which returns -EIO. > > This makes it impossible to reliably get the handshaking state of B and > I wonder if that is intended. I would have expected that TIOCMGET worked > independent of the port being hung up or not. >From what I recall, after hangup happens, you can't do much with the port like this, sorry. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
