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    Subject[PATCH 4.14 31/91] tty: n_gsm: Fix DLCI handling for ADM mode if debug & 2 is not set
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Tony Lindgren <tony@atomide.com>

    commit b2d89ad9c9682e795ed6eeb9ed455789ad6cedf1 upstream.

    At least on droid 4 with control channel in ADM mode, there is no response
    to Modem Status Command (MSC). Currently gsmtty_modem_update() expects to
    have data in dlci->modem_rx unless debug & 2 is set. This means that on
    droid 4, things only work if debug & 2 is set.

    Let's fix the issue by ignoring empty dlci->modem_rx for ADM mode. In
    the AMD mode, CMD_MSC will never respond and gsm_process_modem() won't
    get called to set dlci->modem_rx.

    And according to ts_127010v140000p.pdf, MSC is only relevant if basic
    option is chosen, so let's test for that too.

    Fixes: ea3d8465ab9b ("tty: n_gsm: Allow ADM response in addition to UA for control dlci")
    Cc: linux-serial@vger.kernel.org
    Cc: Alan Cox <alan@llwyncelyn.cymru>
    Cc: Dan Williams <dcbw@redhat.com>
    Cc: Jiri Prchal <jiri.prchal@aksignal.cz>
    Cc: Jiri Slaby <jslaby@suse.cz>
    Cc: Marcel Partap <mpartap@gmx.net>
    Cc: Merlijn Wajer <merlijn@wizzup.org>
    Cc: Michael Nazzareno Trimarchi <michael@amarulasolutions.com>
    Cc: Michael Scott <michael.scott@linaro.org>
    Cc: Pavel Machek <pavel@ucw.cz>
    Cc: Peter Hurley <peter@hurleysoftware.com>
    Cc: Russ Gorby <russ.gorby@intel.com>
    Cc: Sascha Hauer <s.hauer@pengutronix.de>
    Cc: Sebastian Reichel <sre@kernel.org>
    Signed-off-by: Tony Lindgren <tony@atomide.com>
    Cc: stable <stable@vger.kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/tty/n_gsm.c | 11 +++++++++++
    1 file changed, 11 insertions(+)

    --- a/drivers/tty/n_gsm.c
    +++ b/drivers/tty/n_gsm.c
    @@ -2885,11 +2885,22 @@ static int gsmtty_modem_update(struct gs
    static int gsm_carrier_raised(struct tty_port *port)
    {
    struct gsm_dlci *dlci = container_of(port, struct gsm_dlci, port);
    + struct gsm_mux *gsm = dlci->gsm;
    +
    /* Not yet open so no carrier info */
    if (dlci->state != DLCI_OPEN)
    return 0;
    if (debug & 2)
    return 1;
    +
    + /*
    + * Basic mode with control channel in ADM mode may not respond
    + * to CMD_MSC at all and modem_rx is empty.
    + */
    + if (gsm->encoding == 0 && gsm->dlci[0]->mode == DLCI_MODE_ADM &&
    + !dlci->modem_rx)
    + return 1;
    +
    return dlci->modem_rx & TIOCM_CD;
    }


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