From: Daniel Starke <daniel.starke@xxxxxxxxxxx> 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.aspx?specificationId=1516 The changes from 07.010 to 27.010 are non-functional. Therefore, I refer to the newer 27.010 here. Chapter 5.4.6.3.6 states that FCoff stops the transmission on all channels except the control channel. This is already implemented in gsm_data_kick(). However, chapter 5.4.8.1 explains that this shall result in the same behavior as software flow control on the ldisc in advanced option mode. That means only flow control frames shall be sent during flow off. The current implementation does not consider this case. Change gsm_data_kick() to send only flow control frames if constipated to abide the standard. gsm_read_ea_val() and gsm_is_flow_ctrl_msg() are introduced as helper functions for this. It is planned to use gsm_read_ea_val() in later code cleanups for other functions, too. Fixes: c01af4fec2c8 ("n_gsm : Flow control handling in Mux driver") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Daniel Starke <daniel.starke@xxxxxxxxxxx> --- drivers/tty/n_gsm.c | 54 ++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 53 insertions(+), 1 deletion(-) There have been no comments on v2, hence, no change was done. Link: https://lore.kernel.org/all/20220519070757.2096-5-daniel.starke@xxxxxxxxxxx/ diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 58bf4b4aea78..1a6701ae11e7 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -421,6 +421,27 @@ static int gsm_read_ea(unsigned int *val, u8 c) return c & EA; } +/** + * gsm_read_ea_val - read a value until EA + * @val: variable holding value + * @data: buffer of data + * @dlen: length of data + * + * Processes an EA value. Updates the passed variable and + * returns the processed data length. + */ +static unsigned int gsm_read_ea_val(unsigned int *val, const u8 *data, int dlen) +{ + unsigned int len = 0; + + for (; dlen > 0; dlen--) { + len++; + if (gsm_read_ea(val, *data++)) + break; + } + return len; +} + /** * gsm_encode_modem - encode modem data bits * @dlci: DLCI to encode from @@ -727,6 +748,37 @@ static struct gsm_msg *gsm_data_alloc(struct gsm_mux *gsm, u8 addr, int len, return m; } +/** + * gsm_is_flow_ctrl_msg - checks if flow control message + * @msg: message to check + * + * Returns true if the given message is a flow control command of the + * control channel. False is returned in any other case. + */ +static bool gsm_is_flow_ctrl_msg(struct gsm_msg *msg) +{ + unsigned int cmd; + + if (msg->addr > 0) + return false; + + switch (msg->ctrl & ~PF) { + case UI: + case UIH: + cmd = 0; + if (gsm_read_ea_val(&cmd, msg->data + 2, msg->len - 2) < 1) + break; + switch (cmd & ~PF) { + case CMD_FCOFF: + case CMD_FCON: + return true; + } + break; + } + + return false; +} + /** * gsm_data_kick - poke the queue * @gsm: GSM Mux @@ -746,7 +798,7 @@ static void gsm_data_kick(struct gsm_mux *gsm, struct gsm_dlci *dlci) int len; list_for_each_entry_safe(msg, nmsg, &gsm->tx_list, list) { - if (gsm->constipated && msg->addr) + if (gsm->constipated && !gsm_is_flow_ctrl_msg(msg)) continue; if (gsm->encoding != 0) { gsm->txframe[0] = GSM1_SOF; -- 2.34.1
