ModemManager: Handle partial replies in AT+CPIN? (READY without OK)

[Aleksander Morgado <aleksander lanedo com>]

Hi all,

So we have this "AirLink Fastrack Xtend" Sierra Wireless modem [1],
ModemManager uses the generic GSM plugin to handle it.

On PIN check the following flow happens:
  --> 'AT+CPIN?'
  <-- '<CR><LF>+CPIN: READY<CR><LF>'
(see [2] for the logs reported by Thomas Bechtold a while ago).

Once that is received, response is parsed but no successful response is
found, as there is no "<CR><LF>OK<CR><LF>" after the READY [3]. Thus,
ModemManager will wait for more data to come, and ends up timing out
("Serial command timed out").

Once timed out, pin_check_done() gets called in mm-generic-gsm.c, where
both the response GString (with the partial reply) and the GError are
set. If a GError is set in pin_check_done(), the contents of the GString
are fully discarded, and therefore, the pin check is retried up to 3
times and never succeeds.

Now, what would be the proper way to handle this situation? One option
is to make the OK on the reply to AT+CPIN? optional, by parsing partial
replies. See attached patch.

Another option, I guess, is to write a new plugin to handle this
specific case. Maybe there is some other plugin handling it?

Which would be the preferred way to handle this specific issue?

Cheers,

[1]
https://www.sierrawireless.com/productsandservices/AirLink/Programmable%
20and%20Simple%20Modems/Fastrack%20Series/Fastrack_Xtend_EDGE.aspx
[2]
http://mail.gnome.org/archives/networkmanager-list/2011-March/msg00127.html
[3] According to section 9.1.2 of the "AT Commands Interface Guide for
Firmware 7.45" of Sierra Wireless, the AT+CPIN? query reply will never
have an "OK" (quoting here):
        Read command
        AT+CPIN?
        +CPIN: <code>
        Note: No OK

-- 
Aleksander

>From 220c331a23c29e262d807435b1120e96f17c7eea Mon Sep 17 00:00:00 2001
From: Aleksander Morgado <aleksander lanedo com>
Date: Tue, 29 Mar 2011 14:20:15 +0200
Subject: [PATCH] generic-gsm: handle partial AT+CPIN? replies

---
 src/mm-generic-gsm.c |   18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/mm-generic-gsm.c b/src/mm-generic-gsm.c
index 98713b0..a727f00 100644
--- a/src/mm-generic-gsm.c
+++ b/src/mm-generic-gsm.c
@@ -261,8 +261,21 @@ pin_check_done (MMAtSerialPort *port,
 {
     MMCallbackInfo *info = (MMCallbackInfo *) user_data;
     gboolean parsed = FALSE;
+    gboolean partial = FALSE;
 
-    if (error)
+    /* Some Sierra Wireless modems like the 'AirLink Fastrack Xtend'
+     * will send back the READY without an OK, and therefore the
+     * command will time out. Try to handle this. */
+    if (error &&
+        error->domain == MM_SERIAL_ERROR &&
+        error->code == MM_SERIAL_ERROR_RESPONSE_TIMEOUT &&
+        response) {
+        g_warning ("%s: got a partial reply, will try to process it",
+                   __func__);
+        partial = TRUE;
+    }
+
+    if (error && !partial)
         info->error = g_error_copy (error);
     else if (response && strstr (response->str, "+CPIN: ")) {
         const char *str = strstr (response->str, "+CPIN: ") + 7;
@@ -307,7 +320,8 @@ pin_check_done (MMAtSerialPort *port,
         if (!info->error) {
             info->error = g_error_new (MM_MODEM_ERROR,
                                        MM_MODEM_ERROR_GENERAL,
-                                       "Could not parse PIN request response '%s'",
+                                       "Could not parse %sPIN request response '%s'",
+                                       partial ? "partial " : "",
                                        response->str);
         }
     }
-- 
1.7.1