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| author |   Sascha Hauer <s.hauer@pengutronix.de> | 2017-05-31 08:19:05 +0200 |
|---|---|---|
| committer |   Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-06-03 18:48:52 +0900 |
| commit | 71e0779153968c79038a8ed53610d69624115fca (patch) | |
| tree | 20a4d97d4ba762851fb33c61597d8efaa0371a60 /Documentation/serial | |
| parent | Fix serial console on SNI RM400 machines (diff) | |
| download | linux-dev-71e0779153968c79038a8ed53610d69624115fca.tar.xz linux-dev-71e0779153968c79038a8ed53610d69624115fca.zip | |
tty: n_gsm: do not send/receive in ldisc close path
gsm_cleanup_mux() is called in the line discipline close path which
is called at tty_release() time. At this stage the tty is no longer
operational enough to send any frames. Sending close frames is
therefore not possible and waiting for their answers always times
out.
This patch removes sending close messages and waiting for their answers
from the tty_release path.
This patch makes explicit what previously implicitly had been the case
already: We are not able to tell the modem that we are about to close
the multiplexer on our side. This means the modem will stay in
multiplexer mode and re-establishing the multiplexer later fails. The
only way for userspace to work around this is to manually send a close
frame in N_TTY mode after closing the mux.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/serial')
| -rw-r--r-- | Documentation/serial/n_gsm.txt | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/serial/n_gsm.txt b/Documentation/serial/n_gsm.txt index a5d91126a8f7..875361bb7cb4 100644 --- a/Documentation/serial/n_gsm.txt +++ b/Documentation/serial/n_gsm.txt @@ -77,6 +77,13 @@ for example, it's possible : 6- first close all virtual ports before closing the physical port. +Note that after closing the physical port the modem is still in multiplexing +mode. This may prevent a successful re-opening of the port later. To avoid +this situation either reset the modem if your hardware allows that or send +a disconnect command frame manually before initializing the multiplexing mode +for the second time. The byte sequence for the disconnect command frame is: +0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9. + Additional Documentation ------------------------ More practical details on the protocol and how it's supported by industrial |