From: "daniel.starke@siemens.com" daniel.starke@siemens.com
stable inclusion from linux-4.19.232 commit 28ca082153794cf5c98e7bb93d7f30f8ba46bec4
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commit 737b0ef3be6b319d6c1fd64193d1603311969326 upstream.
n_gsm is based on the 3GPP 07.010 and its newer version is the 3GPP 27.010. See https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.a... The changes from 07.010 to 27.010 are non-functional. Therefore, I refer to the newer 27.010 here. Chapter 5.4.6.3.7 describes the encoding of the control signal octet used by the MSC (modem status command). The same encoding is also used in convergence layer type 2 as described in chapter 5.5.2. Table 7 and 24 both require the DV (data valid) bit to be set 1 for outgoing control signal octets sent by the DTE (data terminal equipment), i.e. for the initiator side. Currently, the DV bit is only set if CD (carrier detect) is on, regardless of the side.
This patch fixes this behavior by setting the DV bit on the initiator side unconditionally.
Fixes: e1eaea46bb40 ("tty: n_gsm line discipline") Cc: stable@vger.kernel.org Signed-off-by: Daniel Starke daniel.starke@siemens.com Link: https://lore.kernel.org/r/20220218073123.2121-1-daniel.starke@siemens.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Yongqiang Liu liuyongqiang13@huawei.com Signed-off-by: Laibin Qiu qiulaibin@huawei.com --- drivers/tty/n_gsm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 3e9c8a5b6445..3f08ad7e629a 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -428,7 +428,7 @@ static u8 gsm_encode_modem(const struct gsm_dlci *dlci) modembits |= MDM_RTR; if (dlci->modem_tx & TIOCM_RI) modembits |= MDM_IC; - if (dlci->modem_tx & TIOCM_CD) + if (dlci->modem_tx & TIOCM_CD || dlci->gsm->initiator) modembits |= MDM_DV; return modembits; }