[MTD] [NOR] Prevent erase command invocation on suspended chip

while running stress tests we have met cfi_cmdset_0001.c driver issue.
Working on multipartitional devices with erase suspend on write
feature enabled it is possible to get erase operation invoked on chip
with suspended erase. get_chip() looses information about earlier
suspended erase and new erase operation gets issued. New erase
operations report successful completion, but blocks remain dirty
causing, for example, JFFS2 error messages like:

...
Newly-erased block contained word 0x20031985 at offset 0x00200000
Newly-erased block contained word 0x20031985 at offset 0x00280000
Newly-erased block contained word 0x20031985 at offset 0x00240000
...

The patch below fixes that issue.
Signed-off-by: Alexander Belyakov <alexander.belyakov@intel.com>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

drivers/mtd/chips/cfi_cmdset_0001.c

@@ -795,6 +795,7 @@ static int chip_ready (struct map_info *map, struct flchip *chip, unsigned long
 static int get_chip(struct map_info *map, struct flchip *chip, unsigned long adr, int mode)
 {
 	int ret;
+	DECLARE_WAITQUEUE(wait, current);
 
  retry:
 	if (chip->priv && (mode == FL_WRITING || mode == FL_ERASING
@@ -851,6 +852,20 @@ static int get_chip(struct map_info *map, struct flchip *chip, unsigned long adr
 			spin_unlock(contender->mutex);
 		}
 
+		/* Check if we already have suspended erase
+		 * on this chip. Sleep. */
+		if (mode == FL_ERASING && shared->erasing
+		    && shared->erasing->oldstate == FL_ERASING) {
+			spin_unlock(&shared->lock);
+			set_current_state(TASK_UNINTERRUPTIBLE);
+			add_wait_queue(&chip->wq, &wait);
+			spin_unlock(chip->mutex);
+			schedule();
+			remove_wait_queue(&chip->wq, &wait);
+			spin_lock(chip->mutex);
+			goto retry;
+		}
+
 		/* We now own it */
 		shared->writing = chip;
 		if (mode == FL_ERASING)