gt68xx: added flag to fix stop scan bug

Some scanners (notably the Mustek 1248UB) doesn't like receiving a
STOP scan command when it is not scanning. Flag prevents it my making
sure that START/STOP commands are only ever paired up.

backend/gt68xx.c

@@ -2329,14 +2329,7 @@ sane_cancel (SANE_Handle handle)
       /* some scanners don't like this command when cancelling a scan */
       sanei_usb_set_timeout (SHORT_TIMEOUT);
       gt68xx_device_fix_descriptor (s->dev);
-
-      // FIXME: Temporary sticking plaster fix for models that cannot scan after calling this
-      // function to cancel. [RL]
-      if (s->dev->model->command_set != &mustek_gt6816_command_set)
-        {
-          gt68xx_scanner_stop_scan (s);
-        }
-
+      gt68xx_scanner_stop_scan (s);
       sanei_usb_set_timeout (LONG_TIMEOUT);
 
       if (s->dev->model->flags & GT68XX_FLAG_SHEET_FED)

backend/gt68xx_high.c

@@ -979,9 +979,11 @@ gt68xx_scanner_read_line (GT68xx_Scanner * scanner,
 SANE_Status
 gt68xx_scanner_stop_scan (GT68xx_Scanner * scanner)
 {
-  gt68xx_line_reader_free (scanner->reader);
-  scanner->reader = NULL;
-
+  if (scanner->reader)
+    {
+      gt68xx_line_reader_free (scanner->reader);
+      scanner->reader = NULL;
+    }
   return gt68xx_device_stop_scan (scanner->dev);
 }
 

backend/gt68xx_low.c

@@ -176,6 +176,8 @@ gt68xx_device_new (GT68xx_Device ** dev_return)
 
   dev->manual_selection = SANE_FALSE;
 
+  dev->scan_started = SANE_FALSE;
+
 #ifdef USE_FORK
   dev->shm_channel = NULL;
 #endif /* USE_FORK */
@@ -626,7 +628,14 @@ gt68xx_device_start_scan (GT68xx_Device * dev)
 {
   CHECK_DEV_ACTIVE (dev, "gt68xx_device_start_scan");
   if (dev->model->command_set->start_scan)
-    return (*dev->model->command_set->start_scan) (dev);
+    {
+      if (!dev->scan_started)
+        {
+          dev->scan_started = SANE_TRUE;
+          return (*dev->model->command_set->start_scan) (dev);
+        }
+      return SANE_STATUS_DEVICE_BUSY;
+    }
   else
     return SANE_STATUS_UNSUPPORTED;
 }
@@ -681,7 +690,14 @@ gt68xx_device_stop_scan (GT68xx_Device * dev)
 {
   CHECK_DEV_ACTIVE (dev, "gt68xx_device_stop_scan");
   if (dev->model->command_set->stop_scan)
-    return (*dev->model->command_set->stop_scan) (dev);
+    {
+      if (dev->scan_started)
+        {
+          dev->scan_started = SANE_FALSE;
+          return (*dev->model->command_set->stop_scan) (dev);
+        }
+      return SANE_STATUS_GOOD;  // Essentially a NOP.
+    }
   else
     return SANE_STATUS_UNSUPPORTED;
 }

backend/gt68xx_low.h

@@ -527,6 +527,8 @@ struct GT68xx_Device
   size_t read_bytes_left;
   SANE_Byte gray_mode_color;
   SANE_Bool manual_selection;
+  SANE_Bool scan_started;
+
 #ifdef USE_FORK
   Shm_Channel *shm_channel;
   pid_t reader_pid;