releases/4.14.34/tty-n_gsm-allow-adm-response-in-addition-to-ua-for-control-dlci.patch

   1 From foo@baz Mon Apr  9 13:58:16 CEST 2018
   2 From: Tony Lindgren <tony@atomide.com>
   3 Date: Wed, 3 Jan 2018 10:18:03 -0800
   4 Subject: tty: n_gsm: Allow ADM response in addition to UA for control dlci
   5
   6 From: Tony Lindgren <tony@atomide.com>
   7
   8
   9 [ Upstream commit ea3d8465ab9b3e01be329ac5195970a84bef76c5 ]
  10
  11 Some devices have the control dlci stay in ADM mode instead of the UA
  12 mode. This can seen at least on droid 4 when trying to open the ts
  13 27.010 mux port. Enabling n_gsm debug mode shows the control dlci
  14 always respond with DM to SABM instead of UA:
  15
  16 # modprobe n_gsm debug=0xff
  17 # ldattach -d GSM0710 /dev/ttyS0 &
  18 gsmld_output: 00000000: f9 03 3f 01 1c f9
  19 --> 0) C: SABM(P)
  20 gsmld_receive: 00000000: f9 03 1f 01 36 f9
  21 <-- 0) C: DM(P)
  22 ...
  23 $ minicom -D /dev/gsmtty1
  24 minicom: cannot open /dev/gsmtty1: No error information
  25 $ strace minicom -D /dev/gsmtty1
  26 ...
  27 open("/dev/gsmtty1", O_RDWR|O_NOCTTY|O_NONBLOCK|O_LARGEFILE) = -1 EL2HLT
  28
  29 Note that this is different issue from other n_gsm -EL2HLT issues such
  30 as timeouts when the control dlci does not respond at all.
  31
  32 The ADM mode seems to be a quite common according to "RF Wireless World"
  33 article "GSM Issue-UE sends SABM and gets a DM response instead of
  34 UA response":
  35
  36   This issue is most commonly observed in GSM networks where in UE sends
  37   SABM and expects network to send UA response but it ends up receiving
  38   DM response from the network. SABM stands for Set asynchronous balanced
  39   mode, UA stands for Unnumbered Acknowledge and DA stands for
  40   Disconnected Mode.
  41
  42   An RLP entity can be in one of two modes:
  43   - Asynchronous Balanced Mode (ABM)
  44   - Asynchronous Disconnected Mode (ADM)
  45
  46 Currently Linux kernel closes the control dlci after several retries
  47 in gsm_dlci_t1() on DM. This causes n_gsm /dev/gsmtty ports to produce
  48 error code -EL2HLT when trying to open them as the closing of control
  49 dlci has already set gsm->dead.
  50
  51 Let's fix the issue by allowing control dlci stay in ADM mode after the
  52 retries so the /dev/gsmtty ports can be opened and used. It seems that
  53 it might take several attempts to get any response from the control
  54 dlci, so it's best to allow ADM mode only after the SABM retries are
  55 done.
  56
  57 Note that for droid 4 additional patches are needed to mux the ttyS0
  58 pins and to toggle RTS gpio_149 to wake up the mdm6600 modem are also
  59 needed to use n_gsm. And the mdm6600 modem needs to be powered on.
  60
  61 Cc: linux-serial@vger.kernel.org
  62 Cc: Alan Cox <alan@llwyncelyn.cymru>
  63 Cc: Jiri Prchal <jiri.prchal@aksignal.cz>
  64 Cc: Jiri Slaby <jslaby@suse.cz>
  65 Cc: Marcel Partap <mpartap@gmx.net>
  66 Cc: Michael Scott <michael.scott@linaro.org>
  67 Cc: Peter Hurley <peter@hurleysoftware.com>
  68 Cc: Russ Gorby <russ.gorby@intel.com>
  69 Cc: Sascha Hauer <s.hauer@pengutronix.de>
  70 Cc: Sebastian Reichel <sre@kernel.org>
  71 Signed-off-by: Tony Lindgren <tony@atomide.com>
  72 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  73 Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
  74 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  75 ---
  76  drivers/tty/n_gsm.c |   17 ++++++++++++++---
  77  1 file changed, 14 insertions(+), 3 deletions(-)
  78
  79 --- a/drivers/tty/n_gsm.c
  80 +++ b/drivers/tty/n_gsm.c
  81 @@ -1463,6 +1463,10 @@ static void gsm_dlci_open(struct gsm_dlc
  82   *     in which case an opening port goes back to closed and a closing port
  83   *     is simply put into closed state (any further frames from the other
  84   *     end will get a DM response)
  85 + *
  86 + *     Some control dlci can stay in ADM mode with other dlci working just
  87 + *     fine. In that case we can just keep the control dlci open after the
  88 + *     DLCI_OPENING retries time out.
  89   */
  90
  91  static void gsm_dlci_t1(unsigned long data)
  92 @@ -1476,8 +1480,15 @@ static void gsm_dlci_t1(unsigned long da
  93                 if (dlci->retries) {
  94                         gsm_command(dlci->gsm, dlci->addr, SABM|PF);
  95                         mod_timer(&dlci->t1, jiffies + gsm->t1 * HZ / 100);
  96 -               } else
  97 +               } else if (!dlci->addr && gsm->control == (DM | PF)) {
  98 +                       if (debug & 8)
  99 +                               pr_info("DLCI %d opening in ADM mode.\n",
 100 +                                       dlci->addr);
 101 +                       gsm_dlci_open(dlci);
 102 +               } else {
 103                         gsm_dlci_close(dlci);
 104 +               }
 105 +
 106                 break;
 107         case DLCI_CLOSING:
 108                 dlci->retries--;
 109 @@ -1495,8 +1506,8 @@ static void gsm_dlci_t1(unsigned long da
 110   *     @dlci: DLCI to open
 111   *
 112   *     Commence opening a DLCI from the Linux side. We issue SABM messages
 113 - *     to the modem which should then reply with a UA, at which point we
 114 - *     will move into open state. Opening is done asynchronously with retry
 115 + *     to the modem which should then reply with a UA or ADM, at which point
 116 + *     we will move into open state. Opening is done asynchronously with retry
 117   *     running off timers and the responses.
 118   */
 119