On 2018-04-11 12:06, Greg Kroah-Hartman wrote:
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
If the only valid answer you can get from TIOCMGET for DTR is 'DTR is
active' then there is no point in keeping this functionality. I agree
with
Uwe that one should be able to poll the state of DTR regardless of its
state.
Maarten
--
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
