pixma: retry image retrieval for Canon MF3228. Fixes #442

`read_image_block` needs retry code for this MFP, otherwise `iclass_fill_buffer`
tries to send another `request_image_block` command, which the printer does not
accept when the previous data haven't been read yet, and it enters an endless loop.

This commit is an attempt to fix this issue, by "increasing" the timeout
up to 15 seconds.

It retries 15 times, waiting up to 1100 ms between retries (1s USB timeout with
`HAVE_SANEI_USB_SET_TIMEOUT` + `pixma_sleep`).

backend/pixma/pixma_imageclass.c

@@ -75,6 +75,7 @@
 #define D480_PID   0x26ed
 #define MF4320_PID 0x26ee
 #define D420_PID   0x26ef
+/* also used for MF3228 */
 #define MF3200_PID 0x2684
 #define MF6500_PID 0x2686
 #define IR1018_PID 0x269d
@@ -371,7 +372,7 @@ static int
 read_image_block (pixma_t * s, uint8_t * data, unsigned size)
 {
   iclass_t *mf = (iclass_t *) s->subdriver;
-  int error;
+  int error, i;
   unsigned maxchunksize, chunksize, count = 0;
 
   maxchunksize = MAX_CHUNK_SIZE * ((mf->generation >= 2 ||
@@ -387,7 +388,20 @@ read_image_block (pixma_t * s, uint8_t * data, unsigned size)
       	chunksize = size;
       else
       	chunksize = size - (size % MIN_CHUNK_SIZE);
-      error = pixma_read (s->io, data, chunksize);
+      for (i=0; i<15; i++) {
+        error = pixma_read (s->io, data, chunksize);
+        if (s->cfg->pid == MF3200_PID) {
+          PDBG (pixma_dbg
+              (1, "Using increased timeout for MF3228\n"));
+          if (error == PIXMA_ETIMEDOUT) {
+            PDBG (pixma_dbg
+              (1, "Timeout in read_image_block, waiting 100ms and trying again\n"));
+            pixma_sleep (100000);
+            continue;
+          }
+        }
+        break;
+      }
       if (error < 0)
       	return count;
       count += error;