From: Daniel Starke daniel.starke@siemens.com
commit f4f7d63287217ba25e5c80f5faae5e4f7118790e 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 5.4.8.1 states that XON/XOFF characters shall be used instead of Fcon/Fcoff command in advanced option mode to handle flow control. Chapter 5.4.8.2 describes how XON/XOFF characters shall be handled. Basic option mode only used Fcon/Fcoff commands and no XON/XOFF characters. These are treated as data bytes here. The current implementation uses the gsm_mux field 'constipated' to handle flow control from the remote peer and the gsm_dlci field 'constipated' to handle flow control from each DLCI. The later is unrelated to this patch. The gsm_mux field is correctly set for Fcon/Fcoff commands in gsm_control_message(). However, the same is not true for XON/XOFF characters in gsm1_receive(). Disable software flow control handling in the tty to allow explicit handling by n_gsm. Add the missing handling in advanced option mode for gsm_mux in gsm1_receive() to comply with the standard.
This patch depends on the following commit: Commit 8838b2af23ca ("tty: n_gsm: fix SW flow control encoding/handling")
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/20220422071025.5490-3-daniel.starke@siemens.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/n_gsm.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
--- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -232,6 +232,7 @@ struct gsm_mux { int initiator; /* Did we initiate connection */ bool dead; /* Has the mux been shut down */ struct gsm_dlci *dlci[NUM_DLCI]; + int old_c_iflag; /* termios c_iflag value before attach */ bool constipated; /* Asked by remote to shut up */
spinlock_t tx_lock; @@ -1960,6 +1961,16 @@ static void gsm0_receive(struct gsm_mux
static void gsm1_receive(struct gsm_mux *gsm, unsigned char c) { + /* handle XON/XOFF */ + if ((c & ISO_IEC_646_MASK) == XON) { + gsm->constipated = true; + return; + } else if ((c & ISO_IEC_646_MASK) == XOFF) { + gsm->constipated = false; + /* Kick the link in case it is idling */ + gsm_data_kick(gsm, NULL); + return; + } if (c == GSM1_SOF) { /* EOF is only valid in frame if we have got to the data state and received at least one byte (the FCS) */ @@ -2378,6 +2389,9 @@ static int gsmld_attach_gsm(struct tty_s int ret, i;
gsm->tty = tty_kref_get(tty); + /* Turn off tty XON/XOFF handling to handle it explicitly. */ + gsm->old_c_iflag = tty->termios.c_iflag; + tty->termios.c_iflag &= (IXON | IXOFF); ret = gsm_activate_mux(gsm); if (ret != 0) tty_kref_put(gsm->tty); @@ -2418,6 +2432,8 @@ static void gsmld_detach_gsm(struct tty_ WARN_ON(tty != gsm->tty); for (i = 1; i < NUM_DLCI; i++) tty_unregister_device(gsm_tty_driver, base + i); + /* Restore tty XON/XOFF handling. */ + gsm->tty->termios.c_iflag = gsm->old_c_iflag; tty_kref_put(gsm->tty); gsm->tty = NULL; }