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c6693e6e07
First, checking tty->receive_room to signalize whether there is enough space in the tty buffers does not make much sense. Provided the tty buffers are in tty_port and those are not checked at all. Second, if the rx path is throttled, with CRTSCTS, RTS is deasserted, but is never asserted again. This leads to port "lockup", not accepting any more input. So: 1) stty -F /dev/ttyMI0 crtscts # the mxser port 2) stty -F /dev/ttyS6 crtscts # the connected port 3) cat /dev/ttyMI0 4) "write in a loop" to /dev/ttyS6 5) cat from 3) produces the bytes from 4) 6) killall -STOP cat (the 3)'s one) 7) wait for RTS to drop on /dev/ttyMI0 8) killall -CONT cat (again the 3)'s one) cat erroneously produces no more output now (i.e. no data sent from ttyS6 to ttyMI can be seen). Note that the step 7) is performed twice: once from n_tty by tty_throttle_safe(), once by mxser_stoprx() from the receive path. Then after step 7), n_tty correctly unthrottles the input, but mxser calls mxser_stoprx() again as there is still only a little space in n_tty buffers (tty->receive_room mentioned at the beginning), but the device's FIFO is/can be already filled. After this patch, the output is correctly resumed, i.e. n_tty both throttles and unthrottles without interfering with mxser's attempts. This allows us to get rid of the non-standard ldisc_stop_rx flag from struct mxser_port. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Link: https://lore.kernel.org/r/20211118073125.12283-15-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.